The Samyang 135mm f/2 Lens; Setting It Up and How to Use It

[This is Part 1 of 2 about my new Samyang 135mm f/2 lens imaging system]

Assembling the System

My Samyang 135 mm f/2 imaging system comprises the Canon version of the lens,  a ZWO EAFN, the M42 adapter from Thinkable Creations, and finally the Astrodymium rings. 

The rings (made in Canada) were held up by the changing import rules and regulations about tariffs and fees because I had ordered them from the manufacturer in Canada. The seller was scrambling to sort out what it all meant for any delivery issues and added fees, and was good enough to contact me about what was going on and suggest I cancel the order and buy it from Agena Astro.  Which is what I ended up doing.

The Astrodymium rings/cradle went together like clockwork. I managed to take a couple of missteps by not following the directions and paying attention to the animations in the instructions. I don't use ASIAIR and probably never will, so instead I got a second accessory rail instead. I know when one is accustomed to machined aluminum for tube rings and dovetails the 3D-printed plastic parts may seem a little suspect, but when assembled the entire thing is quite rigid. I don't expect to see any flexure at all.

Through no fault of Thinkable Creations the install of their adapter was more difficult than anticipated. Installing it involves first removing a plate on the Samyang that interfaces with a Canon DSLR and then detaching a spacer ring that's held in place by four tiny screws. The plate came off easily, but two of the spacer ring screws were crazy tight and it took some time (plus a little penetrating oil and elbow grease) to get them out. Other than that the install went well. 

One thing about this adapter that prospective buyers should know: the M42 threads are very long. When I screwed it onto my ZWO EFW it came within a mm of the filter carousel. This seemed dangerous; I imagined it snagging on the carousel and possibly damaging the EFW and filters. 

But fortunately it all worked out. The required backfocus when used with filters is 45 mm. With the adapter in place I have 12.5 (camera) + 20 (EFW) + 5.5 (adapter) for a backfocus of 38 mm. My plan was to add a 7.5 M42 spacer ring to bring it up to 45.5, which I should have been close enough to the magic number of 45.0. Unfortunately those long threads wouldn't allow the ring to fully screw onto the adapter, and instead of 7.5 mm it added 9.5 mm. That put backfocus at 47.5, much too long. Luckily, I had a 5 mm spacer ring on hand. When it screwed on as far as possible there was a gap between it and the adapter face of about 2 mm. This effectively made the adapter's back focus 7.5 mm. Plus the spacer ring's threads don't intrude into the EFW anywhere near as far as the adapter. So if you intend to use the adapter, buy a 5 mm spacer ring, too. The diagram below illustrates how the backfocus works.

Backfocus for ASI 2600 minus tilt ring (red),
ZWO EFW (blue), 5mm spacer (green), and M42 adapter (black);
Diagram is not to scale!

The only thing I didn't get (but should have) in the initial round of orders was a short (150 mm) Vixen-style dovetail, but that's on order and will arrive about the time this is posted. The short length allows the camera/EFW to have full rotation and lets me do flats by resting the light atop the lens shroud.

Imaging at a focal length of 135 mm

Undersampling

Imaging with the Samyang 135 mm f/2 lens is going to be different from my usual imaging mainly because of its short focal length. This will cause what's called undersampling, in which pixels scale is smaller than what the seeing scale. When this is the case, a star's light will illuminate a pixel, but probably not the pixels around it. The star is imaged as a square of pixel size. (When pixel scale is much smaller than seeing scale, a star will illuminate many pixels which makes for nice looking stars at the cost of resolving detail.) 

How do we know undersampling will occur before even taking an image? All we need to do is compare our imaging setup's pixel scale to a value of seeing expected for an imaging session. Suppose we take average seeing as 2.0 arcseconds per pixel  ("/px).

The formula for a setup's image scale is base on the camera's pixel size and the focal length of the imaging telescope or lens: 

Pixel scale (in "/px) = 206 x camera pixel size (in microns) / focal length of lens (in mm)

If you look closely at my recent IFN image, you can see it's on the edge of being undersampled: many of the smaller stars look blocky. According to the above formula, my setup for that had an image scale of 

Pixel scale = 206 x 3.76 microns / 387 mm = 2.0"/px

This confirms the idea that it's mildly undersampled.

Now let's repeat the calculation for the Samyang. We have

Pixel scale = 206 x 3.76 microns / 135 mm =  5.74"/px

This is much larger than 2"/px, so it's safe to assume stars will be undersampled, probably badly.

Drizzling

The way to compensate for undersampling is to drizzle during processing. Drizzling can make those blocky stars rounder and fuzzier, at cost of extra processing time and worse, an amplification of noise. The noise can be reduced by acquiring a large number of light frames and by using a utility like NoiseXTerminator. Drizzling raises the bar on how many light frames to collect and may require frequent dithering. 

If you read forums there seem to be two common answers for how many frames you need -- at least 100 or at least 40. The former comes from those who want the very best images, while the latter is for people like me who are happy with satisfactory results. I'll probably go with 40 for the color frames, but closer to 100 for luminance. There's also disagreement about how often to dither -- once every few frames or with every frame. I'll probably choose to dither after each luminance frame and after each third frame for color channels, if I can reduce the time it takes to dither to something like 20 seconds or so. This might be unrealistic, only testing will tell.

 Dithering

The distance to dither on the imaging camera is generally accepted to be 10 px or so. NINA lets you set this by specifying how many pixels to move on the guide camera. To determine the value to use requires that pixel scale formula again, applied to the imaging system and again to the guiding system:

Imaging Scale = 5.74 "/px (from previously)

Guiding Scale = 206 x 3.75 microns / 130 mm = 5.94 "/px

This means moving one pixel on the guider corresponds to moving 5.94", and moves the imaging camera (5.94 / 5.74) px, or 1.04 px. In other words, the motions of the imaging camera essentially are the same as those of the guider. If I want 10 px dithering on the images, I should use 10 px for the NINA "PHD2 Dither Pixels" setting. The number to use is open to guesswork. Maybe 5 is fine? I'll have to try different values.

Other NINA dither settings are related to the mount. "Settle Pixel Tolerance" is basically how close PHD2 has to be to the guide star before it allows the mount to start settling. You can also set the minimum and maximum times for settling. The defaults for these are 10 and 40 s, respectively. My plan is to experiment with the minimum time and pixel tolerance values to see what works fastest with my mount. 

Some people dither only in RA, but the general advice is to use random dithering.

Exposure time

This is really a guessing game with many trade-offs. For fun I'll use the Sharpcap Sky background calculator for imaging with the Samyang at the Iowa Star party. Sky brightness there is 21.60 magnitude per square arcsecond, and the resulting sky electron rate is 6.49e-/px/s. Read noise is a negligible 1.4e- at gain 100, so to get the sky up to about 1/6 of full well would take 333 s (5.5 minutes). Pretty sure most of the stars in the field of view would be blown out by that. How about simply making sure that the sky signal swamps the read noise? Let's say by a factor of 100? That would only require an exposure of about 21 s. So now I have the exposure time bracketed: 20 to 2000 s!

It's worth noting that some people will shot light frames with only 20 s exposure.

I've been using 90 s exposures and I really like the star color I got in the IFN image so I think I'll stay with that. A test image around the next new moon would be really useful.  

Next Post: Testing

Finished: Integrated Flux Nebula Image

Here's the image at quarter-scale:

1/4 Scale Image

Full-Scale image at AstroBin.

Where to even start with this? How about the data?

Originally there were 13.2 hours of data, but I came across a video in which someone explained how they use PixInsight's SubframeSelector process to cull bad frames. My approach to data culling has always been to keep all that aren't terribly bad, but for this project I thought I'd get tough. Using SFS led me to reject 3.6 hours of data!  To be fair, about a third of that was because of my penchant for starting data collection before the end of twilight. There were very few visibly bad frames as viewed in Blink, so I'm going to call this approach "2 sigma" aggressive, in that it basically culls any frame that has  FWHM, eccentricity, or median values more than two standard deviations above the mean. Note that those rejected frames might be perfectly fine in and of themselves, but relative to their cohort they are of significantly lesser quality. Frames with anomalously low star counts are also culled. An example of this is the set collected during the session that a smoke layer moved in and began obscuring stars in the late morning. Star count fell markedly and I removed frames.

Worth mentioning was the need to use WBPP's Grouping Keywords to make sure that light frames and their appropriate flats were processed together. This was the first time I used it, and it worked perfectly. 

Also, I no longer use dark flats, or "flat darks," if you prefer. Only dark, flat, and bias frames are used for calibration. (Flat and dark frames are now taken for granted at Astrobin, it seems; it no longer asks if you use them.)

Now about the calibration frames, specifically the flats. It seems that most of the time my flat illumination was asymmetric for reasons I don't understand, and this gave the background modelization processing some problems. That big bright Polaris didn't help, either, nor did the fact that most of the image was nebulosity. My first pass used GradientCorrection and that left the right side with a green cast. After playing with that for a while I moved on to DynamicBackgroundExtraction. That didn't clear it up, either. After thinking about it for a while I reverted to AutomaticBackgroundExtractor with a 5th-order function and that did the job. 

Next, those darn satellites. The first processing pass got most of them, but a few stuck around in weakened form. They should have been removed during light frame integration, so I looked at what WBPP was using for rejection and it was Generalized Extreme Studentized Deviate (ESD). Some hunting around took me to a PixInsight forum where it was noted that ESD (using its default settings) wasn't doing a great job with satellites. So I told WBPP to instead use Linear Fit Clipping and that seemed to work better. Not perfect, just better. I will need to find out what ESD settings work best since overall it's probably the scheme to use. It may be that satellites and an image full of nebulosity are always going to be a problem.

I also learned that my usual haphazard application of the XTerminator family has been wrong. It's a processing sin to use NoiseXT before BlurXT and NoiseXT before SPCC. For this image I only applied NXT after taking the image nonlinear.

Here's my workflow for this project with the ">" symbol meaning "creates":

WBPP  >  Cropped channel masters

ABE (color channels) > Backgrounded color channel masters

ChannelCombination > RGB master

ImageSolve > RGB master with astrometry 

SPCC > color-calibrated RGB master

ABE (luminance) > Backgrounded luminance master

BXT (luminance master and RGB master) > enhanced masters

STF and HT > nonlinear masters

NXT > de-noised masters

CurveTransformation (with gentle "S" curve) > enhanced masters

LRGBCombination > LRGB master

assorted tweaks (saturation, sharpness, contrast, etc.) > Finished image

Not shown is an additional DynamicCrop after the ABE of luminance because ABE was a little overaggressive at the left edge. Even with two crops, the final image lost only 4.2% off the short axis and 5.5% off the long axis for a 10% areal loss. The reproducibility of the image framing was impressive. Thank you, NINA. 

Another lesson learned was that the XTerminators could be sped up quite a bit. Normally the necessary files are installed by XTs, but on my old computer the install did not engage the GPU. My graphics card is an NVIDEA GeForce GTX 1050 Ti circa 2018. This post explains how to upgrade a computer to use the GPU for faster XT performance. In my case it sped up the XTs by a factor of 4. I may need to repeat this every time XT does an upgrade.

So how did the processing work out? Mostly I was concerned that the area around Polaris was darkened by background extraction and didn't represent reality. I searched AstroBin for an image I could use as a sort of "ground truth" for what I had done. I found just what I wanted in an image by captured_mom8nts (which I'm guessing is not their real name). It appears to have been taken at a much shorter focal length and so should have suffered much less Polaris bloom, keeping the area around the star reasonably pristine. A little crop/rotate/scale/stretch and it matched my image's scale and orientation:

Comparison: Mine (top), captured_mom8nts (bottom)

I think it fairly obvious that the dark areas on either side of  Polaris in my image match those in captured_mom8nt's image, even though mine is much deeper. I'm happy!

I'm also happy with the star color. Shooting only 90 s exposures may have been the key to that in that it kept stars from saturating. Next time I'll be shooting at f/2, but with a smaller objective so I may keep the exposure time as is. 

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All the components of my new Samyang 135 mm f/2 imaging system have arrived or are on their way. Next time I'll have a picture of it all assembled and possibly already taken on its first test drive!

Back From NNSF: Tamron 135mm Verdict

NNSF 2025 was better than average; I had two solid nights of imaging. I might have had three if I had stayed over on Sunday night--but I'm not really sure if it was clear that night.

The first night (Wednesday) was a dusk-to-dawn session and I used my FSQ-106 to collect the green and red channel data I needed to complete my integrated flux nebula image. Plus a few more luminance and blue frames, just because I could. I'll be processing that data in the next couple of weeks.

Thursday night was lost to clouds, but Friday night was fine and I went until about 3 A.M. using the Tamron for wide-field views. The Tamron was stopped down to about f/5.4, basically reducing it to a one-inch f/5.4 telescope that no one in their right mind would use for imaging. It wasn't surprising that the results were less than adequate. Here's the Veil:

Final result, significantly cropped to hide flat frame errors

This is based on about 60 frames in the LRGB ratio of 2:1:1:1, with each frame a 120 s exposure. Bias, Dark, and Flat frames were applied; processing was in PixInsight.

That's not completely terrible if you only look at the much scaled-down size. But the faults are still there.

There's an overall blue cast to stars, due to problems with the red focal point and probably chromatic aberration. 

The stars are quite bloated, probably because of the tiny aperture used. I tried to reduce them as best I could, but you can see how the Veil is almost lost in all the stars.

There was good news, the new mounting ring made rotating the camera easy and reliable. And stopping down the lens and processing with BlurXterminator made the stars nice and round even in the corners:

PixInsight Aberration Inspector Panel

The red focal point was substantially different from what NINA expected based on filter setoff training. The Astrodon LRGB filters I use are essentially parfocal, so I have to assume this is some sort of lens fault.

Final judgement: I don't want to do wide field at a sluggish f/5.4, I don't like bloated stars, and autofocus is something I can no longer live without. This image just isn't what I consider acceptable, and I also like to guide and dither. Although the above image used neither and turned out fine -- the G-11 tracks well enough at 135 mm -- I think some dithering might be helpful. So: the Tamron will be relegated to daytime use and I'll need to find a replacement. How about that Rokinon? Or maybe the identical Samyang? Why pay an extra $50 for the brand name?

Here's the kit to go with a 135mm f/2 Samyang: A cradle from Astrodymium that will let me attach a guide camera and a ZWO EAF, giving me my precious autofocusing!

Now let's address the backfocus issue, something that has plagued my use of Canon lenses with the ASI 2600. The desired backfocus is something like 45 mm (44 mm + 1 mm to compensate for the filters I use). Conventional wisdom says you must be within +/- 2 mm, and that being within +/- 1 mm is preferred.

Solution 1 is to use a Canon to M42 adapter with maybe a 1mm spacer ring: ASI2600 (12.5 mm) + ZWO EFW (20 mm) + Canon adapter (10 mm) + spacer ring (1 mm) = 43.5 mm backfocus. That's off by 1.5 mm, which might be enough to show up visually. It would be nice to slip in another space ring, but there just isn't enough thread depth for it.

Here's a video by someone with exactly the same gear I would be using, and she's happy with it.

I don't know if that will hold true for me, though. Maybe variations between lenses might be enough to require a closer backfocus match. Maybe imaging at f/2 changes the amount of filter backfocus compensation? It would be nice to have some options.

Which brings us to Solution 2: ASI2600 (12.5 mm) + ZWO EFW (20 mm) + spacer ring (1 mm) + (extension spacer) 5 mm + spacer ring (0.9 mm) + M42 adapter (5.5 mm) = 44.9 mm. (I don't have two 1 mm spacers.)

There's even a Solution 3, since I have a 7.5 mm extension ring: ASI2600 (12.5 mm) + ZWO EFW (20 mm) + (extension spacer) 7.5 mm + M42 adapter (5.5 mm) = 45.5. I actually prefer this as it it eliminates the spacer rings and allows all the threads to engage more fully.

All the orders have been placed, and things start arriving in only two days! Plenty of time to get this assembled and running before the Iowa Star Party in October.

Next time, the IFN image and a look at the new Samyang!

Fast Deliveries Mean an Unexpected Update: NEEWER to the Rescue

A couple of things came in so I'm doing this happy update:

135 mm Tamron & ASI in new mounting ring
atop a NEEWER dovetail atop an ADM vixen to Losmandy D adapter

The new 90 mm mounting ring arrived and it fits my ASI 2600 like a glove. Plenty of room for the entire optical train to rotate through 360 degrees, too. 

There's always a catch, though. The mounting ring comes with a foot appropriate to sitting on a quick-release tripod head rather than anything commonly compatible with astronomy mount saddles. If only there was an adapter to mate a dovetail to those two little holes on the ring? 

But there is, at Amazon. It's a NEEWER 9 inch Vixen dovetail. It mates perfectly to the ring using the ring's included bolts. The NEEWER slips into an ADM saddle adapter, so the whole thing will ride atop my G-11. Granted this does look like a bit of a kludge, but it's solid. 

I have a finder saddle to fit on the top of the ring, so I'll be able to guide and dither should I choose. If I make it to NNSF this will come along. I'll also bring a couple of other lenses for testing.

The last bit on order is a filter adapter that will act as an aperture mask for the Tamron. At this point it has departed China; delivery is still expected on the 18th.

Revisiting the Tamron 135 mm Lens.

Perfection is a terrible thing, being both difficult to define and impossible to achieve. It can stand in the way of getting something done, and lead a person to reject things that fail to meet your estimation of perfection. It has led me to consider getting rid of my old Tamron 135 mm lens. (Yes, I'm talking about that lens again. I could subject you to more battery talk, but no one really wants that, right?)

The Tamron was dropped from my integrated flux nebula imaging project for two primary reasons: the mounting ring I had made it all but impossible to consistently orient the camera, and it was showing too much aberration. 

I've now purchased a much better ring from Agena Astro. This ring and the dovetail it's on will also help with the limited rotation the old one allowed. The extended ring release knob release knob also eliminates the difficulty in turning the old knob, which was tight against the ring itself. I doubt the new ring will be "perfect," but it may be much more adequate that what it replaces. 

As for the aberration, I blamed that problem mostly on incorrect backfocus. I had assumed 45 mm was needed (44 for the camera plus 1 for the filter). My setup had backfocus of 12.5 (camera) + 20 (filter wheel) + 10 (canon to M42 adapter) plus 1 mm (spacer ring) for a total of 43.5 mm. This was 1.5 mm short, and the way people talk in forums that was seriously incorrect. 

But what if it wasn't? Watch this video. The imager is attaching an ASI 2600MM (my camera) with the same ZWO EFW as mine, a 135 mm lens (not the same as mine, sadly. She had the Rokinon 135 mm lens that I continue to lust after), used the same Canon-to-M42 adapter as mine, and a 1 mm spacer ring for a total backfocus of 43.5 mm (the same as mine). That gets her nice flat fields, so it's probably the case that my backfocus isn't the issue, it's the lens quality. 

A late-1970s Tamron at f/4 is no match for a modern lens like a Rokinon even if their inflation-adjusted prices aren't all that different. The obvious fix is to stop the Tamron down, perhaps to f/5.6. To do this without spiked stars requires a 58-24 mm step down filter adapter. (I found a 58-25 mm adapter on eBay ($2 + $15 for shipping), so I'll be shooting at f/5.4, which is close enough. Delivery date is projected to be August 18, two days before the Northern Nights Star Fest. 

These two issues settled (perhaps) the Tamron will continue to live.

If it arrives in time, I'll take it north and skies permitting put it to work on this:

Heart and Soul Nebulae with the Double Cluster

This is a very rich field ...

Above image with annotation

... with so much nebulosity and open clusters, too!

First priority will be collecting the green and red channel light frames to complete the IFN image. That should take only one night with time left over for more luminance frames. The Tamron will come out on the second clear night, assuming there is one. If the Tamron's aberration is still significant, I may switch to my 200 mm Olympus lens which has already proven itself to be flat-field at f/4. The Olympus will narrow the field to just the two nebulae.

Just in case NNSF produces four nights (!) of clear sky I'll bring along the 200 mm lens for some fun! And maybe even my 50 mm Olympus lens, why not.

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In terms of comfort sky clarity this summer has been one of the worst on record, with days and nights alternating between excessive heat and humidity, rain and severe weather, overhead smoke, and very poor air quality. In fact, half the days since mid-May have featured one of these unpleasantries (per the State Climate Office). My hope that the smoke will diminish before NNSF is only that, a hope. I'm fairly sure the fires will be much reduced by the time of the Iowa Star Party in October, but it would be nice if the new moon in September is also smoke-free!

We're currently in the midst of a multi-day air quality alert covering the entire northern Midwest. Yesterday morning the air smelled of sulphur and the sky has been a perpetual brown.

Air Quality Map @ 2 PM CDT 08/01/2025 (graphic from fire.airnow.gov)

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August 1 brings more tariffs, and it's time to check on that Rokinon lens. The "new" tariff on on South Korea is about the same as the existing one, so it's no surprise that the Rokinon is holding steady at $449.

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That's all for this time, next post is in late August with results from the NNSF (I hope!)

One Channel; Dozens of Bites

Another camping trip to Lac qui Parle State Park is over and it was a partial success. Let's start with the good news first: I got the blue channel data I needed:

Blue Channel of IFN

This is based on 1.72 hours of total exposure. Blue is usually the weakest channel in terms of signal and to me this looks decent. I'll try to get about the same exposure time for green and red. The strongest blue signal seems to be in the area just below Polaris; this may make that area whitest, which would be in agreement with what I've seen in other images.

[ Compare this to the luminance channel image in the previous post. Blue looks much less contrasty, right? Consider that the blue channel has only 1/3 (or so) of  the luminance signal, and that the above is based on 69 subs compared to the luminance's 177 subs; you can roughly figure this has an equivalent exposure of only 1/8 of the luminance. It didn't get lifted nearly as far above the background, so less contrast. ]

See the copyright notice? That's because my little blog is now getting scraped two or three times every day. Probably not because it's worth scraping, but simply because it exists. I can't really do much of anything that's effective to stop it without adding a CAPTCHA-like layer that would force everyone to choose which squares are motorcycles, or traffic signals, or whatever bots can't easily distinguish. I don't like those things, so I won't subject others to them.

Now the unfortunate part of the trip. The first night's imaging ended prematurely when somehow PHD2 became convinced it was using my imaging camera as the guide camera. This wreaked havoc with things: I started getting repeated timeouts, and a couple of the frames suffered from strange excursions probably caused by calibration mismatch due to different focal lengths. I shut down the sequence and tried troubleshooting, but it was simply not happy. It was already 1:30 A.M. so I decided to give up and get it worked out the next day. Here's what the misguided guider was doing on two of the frames:

Excursions along one of the guider axes.

This was clearly along one of the guider's axes. The guiding display of corrections looked like a strong square wave. 

The next day was unpleasantly warm (almost 90 F and dead calm). I redid PHD's hardware profile and collected the new dark/bad pixel frames it demanded. Things seemed to work; there was a steady stream of images. It also needed a new calibration, something I could only do once it was dark. As dusk fell the mosquitoes attacked in force. My Coleman shelter worked reasonably well to protect me, but all this reconfiguring was making me repeatedly get in and out of the protected area, each time allowing dozens of hungry mosquitoes in. Neither the usually effective Ultrathon or DEET products kept them off me. It was not fun.

There were thunderstorms already west of me in South Dakota, the last satellite images showed high blowoff from them headed directly my way. The forecast was for rain and possibly severe weather around 5 A.M., meaning I'd have to break down everything and pack it away before turning in. 

Between all that and how the bites on my arms and hands were welting up I decided to pack it in and  get a good night's sleep. As it turned out there was rain but the severe stuff went elsewhere. I was glad to have bailed on the night. 

I don't think I'll be making any more mid-summer trips to the park, it's just too buggy for this imager. What a change it was from the previous month's visit!

I'll only have some of the July new moon to see about collecting the red and green frames as my wife is having her second knee replacement done on the day of the new moon. I'll probably just wait for the Northern Nights Star Fest at the end of August, as that should be cooler, darker, and will have longer nights. Or, if that's completely clouded out the Iowa Star Party in October or any clear, dark nights I can get out to Eagle Lake.

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Tariff Watch: The Rokinon lens remains in stock at B&H at $449. This price is 22% above the February pre-tariff price, which is very close to the current tariff of 26% with South Korea.

Reservations, Smoke, and One Night of Imaging

A few things from a less than fully successful week of dark-sky camping:

Reservations

The initial state park reservations I had were for three nights starting Tuesday. Clouds and rain looked very likely to wipe out the first two nights so I cancelled the reservation and made another for 3 nights starting Thursday when the forecast was much more favorable: one iffy night followed by two that were perfect.  I decided to get everything set up and running that iffy night after seeing the Sun wink out as it set into a heavy smoke layer on the northwest horizon. This turned out to be a good move as this would be the only useable night. The heavy smoke arrived by Friday morning, when two hours after sunrise the Sun was a dim red ball you could look at directly. 

Lesson learned: Minnesota state parks offer same-day reservations.  Next time I'll wait until I'm sure the night will be clear to make my reservation.  All my things are very well organized and I can pack the car and be on the road in less than an hour. My preferred dark-sky camp, Lac qui Parle, is lightly used and usually has unpowered pull-ins available.

Mount Safety Limits

By the time I was ready to shut down that first night my mount had rotated to the point that it was well beyond its safe travel limit. This didn't really matter as looking to Polaris allows much further travel than is usually safe, and the G-11 mount tracks nicely even when it's over-rotated and the counterweight shaft is well beyond horizontal. 

That said, what I expected was a meridian flip sometime around midnight. When that didn't happen I recycled the system and expected go-to would put the scope on the correct side. It didn't. I could see that eventually I'd run the camera against the mount and decided to let it go right up to that point before stopping. 

I got enough frames that night, but in a month when I return to shoot color frames I'll have to stop even earlier in the evening. 

Lesson learned: I need to configure NINA and my Gemini-II mount control to properly handle flips.

Here are two videos that I found useful for doing this and for setting up NINA for flips:

https://www.youtube.com/watch?v=Rk8uOikHPb4

https://www.youtube.com/watch?v=0N0U5chskCQ

There's also a very useful spreadsheet available to members of the Gemini-II user group on groups.io (See the second link above for how to use the spreadsheet.)

I've made the changes to my Gemini-II and go-to now seems to put the telescope on the correct side based on the limits. Seeing if automated meridian flips work will have to wait for a night under stars.

The Coleman Bug Shelter (Previously mentioned here.)

This was my first night out with the shelter, and it worked great--no gnats, no mosquitoes inside. I sat in the shelter linked to the scope with a 16' active USB 3 cable (which was also getting its first all-night imaging test). There wasn't a single glitch. The only awkward part of this is doing polar alignment, when I (and the laptop) need to be at the mount to make adjustments. Once that's done, it's back into the Coleman. It was so comfortable in there that I spent most of the evening relaxing with a good book.

Lesson learned: I'm ready for next year's Nebraska Star Party and its all-night supply of mosquitoes. Will the shelter, even when staked down, be able to endure the winds of Nebraska?

The Results

If the Eagle Lake Observatory setting is Bortle 4 plus a bit, then Lac qui Parle with Thursday night's smoke was Bortle 4 minus a bit: definitely darker than Eagle lake, but certainly it wasn't the Bortle 3 I've seen  there before. Despite that, I gathered 113 luminance frames. Seven were discarded for being in twilight, and one was lost for poor tracking. Adding the new 105 frames to the previously collected 72 Eagle Lake frames brought me to about 4.4 hours of total luminance exposure.

Here is the result, as produced by PixInsight's WBPP and some modest postprocessing of my own:

IFN (luminance, 4.4 hours)

This is much better than my 72-frame image, and it may be all the luminance I need to collect. Using the 3:1:1:1 "standard LRGB model" what's left to shoot is perhaps an hour and a half of each color channel. I have the new moons of June and July to collect my color frames.

Lesson learned: some smoke at a Bortle 3 may be better than clear sky at a Bortle 4+ site.  Given enough good nights I'd still like to add more luminance and get to 6:1:1:1, but good nights around here seem all too rare.

Satellites Galore (with bonus Trek Humor)

These are the satellite tracks rejected by PixInsight. There are a lot of them in 4.4 hours!

"Go home, Tholians, you're drunk"

That's all for this post. In a couple of weeks the moon will go away again and I'll try to get the color data that will bring this luminance to life. 

Reprocessed IFN Using PixInsight's WBPP

The image in the last post was really not very well processed, with the culprit being me. I suspect I twice subtracted bias or something. It was so bad that I decided to reprocess immediately, adding in some color channel data I collected. The best way I could see to avoid messing up again was to plunge right into using PixInsight's popular Weighted Batch Preprocessing script (WBPP).

Was it easy to use? Yes! If you disagree, I suggest watching the series of WBPP tutorials by Adam Block.

Did it work well with all the default settings? Yes, it did for me. The only step I skipped was Cosmetic Correction. I'll have time to learn how to incorporate CC between now and when I need to process new data collected later this month. 

Was it fast? I fed it my 72 luminance frames, 36 color frames, 100 bias frames, 30 dark frames, and 100 channel flats. WBPP made master frames, calibrated my light frames, and registered and integrated the lights, and finished by doing a crop of all four channels. All that in 51 minutes. Wow!

I know there's some sort of WBPP Fast Integration thing that can reduce this even further, but I'm saving that for the future.

The WBPP result is so much better. Here is the master luminance after post-processing:

Polaris IFN as processed by PixInsight WBPP

The full scale image is on AstroBin. Because Astrometry.net as employed by AstroBin seems to have issues with this, I'll pass along ASTAP's solution:

ASTAP solve of above image.
North is up; the celestial pole is a little beyond the top edge

This is exactly the composition I want: Polaris sitting at top center and giving the illusion of shining its light down on the nebulosity. Which it probably isn't actually doing, but artistic license is allowed, right? 😏

Not only is that ugly vertical banding gone, the stars are better shaped. ASTAP puts the tilt at only 3% ("none") compared to the previous "moderate." I continue to be amazed that so much nebulosity can be captured with less that two hours of total exposure at a Bortle 4 site with a nasty high-in-the-sky first quarter moon.  

The color image was not adequate and you won't see it here. It looked as if the background flattening of the three channels had gone awry. I'll need to play with the color channels and see if I can do better.

The night I collected the color frames give me hope for my camping trip. PHD2 guiding was almost perfect. Of 36 frames, none were rejected. With dithering turned off there were no hiccups. I retrained PHD2 beforehand, this time with the correct focal length for the guide scope, and it seemed better behaved. 

Reacquiring the image area worked great. The evening was the third time I told NINA to go to the target. It seems to be doing this quite well: almost nothing has been lost due to mistargeting: 

Portion of full image removed by WBPP cropping (red)

Everything considered, it all worked as intended. That's a little scary; I have to wonder what mischief my hardware has planned for me when I take it to the dark-sky campground.

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While the tariff wars have devolved into confusion over what, when, and how much, the Rokinon 135 mm f/2 lens for Canon hangs in there at the same old $449. If you've been watching the astronomy gear dealerships, you've probably noticed that many items are no longer in stock. Buyers seem to be rushing their purchases to avoid the expected higher prices.

Integrated Flux Nebula Mini-Test Result

 Let's get right to the image:

Polaris IFN luminance trial

The total exposure was a scant 1.8 hours (72 x 90 s). NINA ran the acquisition and PixInsight handled the processing. Flat frames were used. The nonlinear stretch was the PI Screen Transfer function and no attempt was made to enhance contrast beyond what it provided.

This is so far beyond my expectations that I don't know what to write. It was a not-very-dark site, the moon was at first quarter high in the ecliptic between Cancer and Leo, and there was a thin layer of smoke aloft. I really didn't expect to get much if any nebulosity in the image. But there it is.

The night's goal was to fully test the imaging setup and perhaps answer a few questions:

• Would go-to compose the image reliably? I started it once, collected a dozen frames, shut it all down, parked the scope and did the entire startup again. Plate solving shows the center changed by 67.5 seconds in RA and 7 seconds in Dec. Translating the RA difference to arcseconds at the equator, it's actually more like 27 arc seconds. That's total shift of about 28 arcseconds. The difference in image axis rotation is also tiny, about 0.11 degrees. So the answer is Yes, go-to works very well!
• Would guiding work so close to the pole? I had made some changes in PHD2--activating multi-star guiding and predictive PEC, and using the calibration assistant to make sure that was done optimally. Through the evening it collected 72 light frames, and only one had to be rejected (when PHD2 timed out after a dither). Tracking was next to perfect. I'm nor sure the ASI 2600 benefits much from dithering, so I'll disable it.
• Some people have indicated issues with field rotation when guiding near a celestial pole. I saw no sign of that. Possibly the excellent polar alignment from PoleMaster should get credit for this.

I do like the composition of the image, with Polaris shifted off center northward and looking as if it's shining light down onto the nebulosity. It's nice to see that the offset doesn't produce any significant internal reflection.

There are issues with this image, though. Although ASTAP reports moderate tilt I don't see any evidence of it. (Maybe it's some sort of algorithmic issue?) There are a lot of vertical bands in this that snuck in during the processing. I'll have to find a way to make sure to avoid them. [EDIT 12 May: see the reprocessed image here.]

PHD2 was doing something that seemed odd. Every now and then it would make a too-large declination adjustment and then follow that with smaller corrections. This may also have been my fault as I had the wrong guide scope focal length entered. This has been corrected, so I'll see if that takes care of the issue. 

Tonight I'll be out again to test my RGB acquisition scheme. Basically, I'll try the good old 3:1:1:1 channel ratio, meaning 24 frames for each color channel. How will the colors turn out?

My 135 mm Tamron Delusion Ends, It's Plan B now

I really thought I could get away with using my old Tamron lens for imaging Integrated Flux Nebula (IFN), but it's not to be. The number of minuses kept growing as I spent more nights practicing with the setup. I realized that my desire to use the Tamron and was blinding me to the issues that doomed it.

The greatest difficulty was being unable to rotate the field of view in a reproducible manner. This happened every night I used the setup with one night being 45 degrees out of kilter from the others. Keeping the camera orientation consistent between multiple imaging sessions is essential; without this, some of the field will need to be discarded during stacking. It became obvious that the amount of lost field would probably be substantial, resulting in a much retained field of view. The advantage of the wide 135 mm field of view would be lost. I think the cause was the ring clamp I was using to join the lens and camera to the dovetail. To permit manual rotation of the camera this ring had to be loosened and retightened many times, resulting in misalignment.

Image quality was also not what I wanted. There was no reasonable solution for the back focus error and I would be stuck with strong aberration needing to be corrected by BlurXTerminator. I knew some residual aberration remained, and I was concerned that this might show itself during the aggressive processing I would use to draw out the IFN. 

I came to realize that the stepdown ring I was using to produce spikeless stars was causing severe vignetting. While flat frames could somewhat compensate for this, too much signal was being lost -- again diminishing the effective size of the field of view. Using the lens's internal blades to stop it down was an alternative that created large, flaring spikes around the stars. I found this unacceptable.

Plainly, the lens was not up to the purpose and it was time to move to Plan B.

Plan B

The fallback is to use the FSQ-106 + focal reducer operating at a focal length of 387 mm and focal ratio of f/3.65. This California Nebula image used that configuration and gives you an idea of what it can do. The advantages are many over the Tamron: 

• 17% increase in speed (f/3.65 vs f/4)
• A very flat field with modest vignetting  
• An actual rotation ring
• Amenities like autofocus, autoguiding and dithering, easier creation of flat frames, and automatic meridian flipping

This is a much heavier scope to tote around, but the only real disadvantage it has is the smaller field of view. Here's a comparison:

135 mm Tamron field (outer box) vs 387 mm FSQ field (inner box)

The star cluster is no longer in the FOV, which is fine as the IFN is the real target. Does the smaller FOV (about 3.5 x 2.3 degrees) include enough IFN to be worth imaging? This image of Polaris IFN by another imager has essentially the same FOV as my setup will produce. I think there's enough IFN there to make it worthwhile particularly if Polaris can be reduced in size. I'll also compose the image to have Polaris much closer to the north edge of the frame, making more room for the IFN. 

Other aspects of the comparison image are worth looking at.

The scope used was an f/5.5 refractor with a flattener that didn't affect the focal ratio (so far as I can discover). The camera, an ASI 6200 color camera, has a quantum efficiency about the same as my ASI 2600 mono camera. The total integration time was 5 hours and 10 minutes. My thought is that if I want a reasonably deep image with low noise I should try to get at least twice the total time that went into the image. I'll probably use a plan that requires two nights of imaging: 5 hours of luminance one night, 3 hours of Chrominance another night. That's roughly the equivalent of 11.7 hours of one-shot color gathered at f/5.5. 

Yes, I know, that's a LRGB ratio of 5:1:1:1 and instead of the usual 3:1:1:1. I just like working with luminance; one night a few years ago something glitched and I ended up shooting only luminance. The final ratio was 6:1:1:1 and the result was quite nice (in my opinion, of course).

The comparison image was created using 5-minute light frames, which is probably why star colors are muted and Polaris is bloated. I've had much better luck with shorter exposures, and may simply go with 90 s lights. Both of my linked images used 90 s lights exclusively.

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Tariff watch: the Rokinon 135 mm lens (Plan C) is holding steady at $449 and in stock at B&H.

IFN Setup Passes Its First Tests (With Help From BlurXTerminator)

Last night was good for running some tests on my integrated flux nebula (IFN) imaging setup. I was able to take test frames at different exposures (60, 90, 120, 180 and 240 seconds) and test go-to and tracking. Everything came out well, or as well as could be expected and many questions were answered.

Did Polaris throw an internal reflection?

I stretched a 240 s exposure using PixInsight's Boosted Autostretch and there was no evidence of any internal reflections. It's possible something will show up in an image stack, but this suggests even if it does it will be faint.

Was the field suitably free of aberration? 

Here's a visual comparison of the corners and center in one of the 2 minute exposures (click for full scale). This is basically a raw frame; it's only been brute-force flatted and then delinearized with PI's default stretch.

Pretty awful, isn't it? My guess is that the aberration is coming from backfocus being significantly off. How much off, and in what sense? I'd use NINA's aberration inspector to find out, but this is a manual-focus lens. Sadly, my ability to change the backfocus is next to zero. Skip the following paragraph if talk about backfocus bores you :)

My required backfocus should be about 45 mm (44 for the lens plus1 for the filter), and I'm currently at 42.5 mm. The best I can do to increase this is by adding a 0.8 mm thin spacer or whatever the thinnest M42 spacer ring is (probably 5 mm?). Decreasing the backfocus would require a Canon-M42 adapter that's thinner than 10 mm or a filter drawer that's thinner than 20 mm and can be adapted to use 36 mm filters. Increasing the fun is that this lens is actually at heart a Tamron Adaptall lens circa 1980, fitted with a ring to make it compatible with OM-1 cameras. Both date back to the 1970s, so good luck finding things to take advantage of any of that. And yes, I looked into having a custom adapter built, both Canon to M42 and Olympus OM to M42, and they can't do it in a way that works for me (not to mention it would be $$$ if they could).

Fortunately the aberration can be adequately dealt with using BlurXTerminator (BXT). The corner diagram below shows how well BXT fixes things using the very non-aggressive settings of zero for both its "Sharpen Stars" and "Adjust Star Halos" parameters:

The improvement is almost miraculous. All the corners look sharp. So the lens passes this test thanks to processing with BXT.

Can the lens reach a decent focus?

The focus you see is the result of a few minutes of shooting test frames and making very tiny manual adjustments (just like in the old days before I had an electronic focusing motor). I think it's quite good. Yes, I'd love to have NINA do the focusing for me, but that's not going to happen.

I will need to stabilize the focus wheel to avoid accidental movement; a piece of tape should work.

Was there tilt?

A first look at tilt as calculated by ASTAP gave this.

It's not so much tilt around one axis as it is a sign of the aberration. ASTAP considers the tilt severe (see the small text along bottom of image). After BXT has been run the results confirm the improvement seen in the second corner diagram above: 

Star size outside the center is dramatically reduced and ASTAP now considers the tilt to be "almost none." This means I won't need to add the tilt plate or shims.

What about the mount and Go-To?

The mount slewed to Polaris and plate solved without fault. Manually correcting the rotation was simple and fast. The required rotation was only eight degrees, so the riser wasn't necessary and will be removed.

How was the tracking?

The center stars in the pre-BXTcorner diagram were nice and round so I'll assume tracking is close to perfect. The corner stars in the post-BXT are fine, too, so there's no appreciable field rotation in a 2 minute span.  I use PoleMaster for polar alignment, and it provides almost no visible rotation even over a multi-hour session, so I think that tracking should be more than adequate.

In other words, there's no need to add autoguiding or fiddle with PEC.

Were there any composition issues?

The amount of camera rotation required was only eight degrees from the filter wheel's long-axis up position, meaning that the riser wasn't needed. I'll remove it and the system will be a little sturdier.

Oddly NGC 188 was not quite where I wanted it. It's a touch close to an edge than I expected. I'll have to look at the instructions I gave NINA.

Summary

Everything worked better than expected with help from BXT! Basically, the system is ready for field use, although a little more work remains to get it set up for dew control. Because BXT removed the aberration using very nonaggressive settings, I don't think it will damage the IFN.

A major concern was the mount: would it behave itself for a target so close to the celestial pole? It slewed and centered on the target without difficulty. Manual rotation was easy and the riser won't be needed.

I think the ASI-2600 will do fine without dithering, but I may try that anyway with the PixInsight manual dithering tool.

It looks like almost any exposure will serve well; even a 4-minute exposure had nice round stars; I think I'll probably use 2 minutes for all four channels.

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My reading of Hugo Award winning novels is winding down. I skipped back to the 2000 winner, A Deepness in the Sky, by Vernor Vinge, and it was slog to get through. A few times it was almost a DNF (did not finish). I just couldn't connect with the author's writing style, his use of many side characters that were of little consequence, and the too-happy ending that seemed rather forced. For some reason he felt compelled to add a bloated epilog that served mainly to punish readers. Most of the Hugos have been worth reading, but not this one.

Up next is the 1939 Retro Hugo Award winner, The Sword in the Stone by T. H. White. Yes, it's that sword in that stone; the story has spawned a number of adaptations (the 1963 animated version by Disney is probably still the best known.

This will be the end of the Hugos for me, at least for a while. Maybe I'll start another reading marathon when my wife has her other knee replaced.

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It's lithium battery maintenance time: all the batteries have been fully recharged and then discharged to about 50% of capacity. Just before Northern Nights Star Fest I'll be bringing them up to full charge and selling/swapping them at 80% below list price. I'll provide a full description of what I'm bringing to NNSF in an August post.

A Few More Days to Clear Sky?; A Product to Avoid

Spring progresses slowly, but it appears that next Tuesday night (today is Saturday) will finally be clear and suitably dark for testing the things I need to verify about my IFN imaging setup before it goes on the road. In the meantime I've been putting together the traveling kit so that I can have all the cables and such needed for the project ready. It's also been time to top off all my lithium batteries. 

Lithium batteries are remarkably tolerant of abuse. The can abide deep discharges if you can get them to a charger within a day or so. Almost every lithium battery of any reasonable size now includes a battery management system that prevents too-rapid discharge or overcharging. The batteries also tolerate temperatures that I wouldn't! 

Maintaining a lithium battery is easy, too, even in the seasonal sport of astrophotography. At the end of the imaging year, just make sure they're they've been discharged to about 50% capacity, then every three months bring them up to 100% and back down to 50%. When you resume imaging and their use becomes more continuous just keep them fully charged. 

Yesterday I started the springtime full charge of the battery pack I use to power my laptop, and it revealed something I should have known. The pack in question is a pair of 15 Ah batteries in parallel, so I thought to use my 10 A charger.  The pack's only port is a 12 V automotive socket and the charger was sending 10 A through a fused automotive plug. All was fine for a while, but then the charger indicated it had shut itself off and there was a faint aroma of overheated plastic. That's never good.

Inspection of the plug showed the fuse was intact, but that the coiled spring at the base of the fuse was misshapen and the plastic around it had melted. Supposedly 12 V plugs can handle 120 W (10 A @ 12 V). At the point it started to overheat it was probably being asked to handle around 135 W, which evidently was too much for it. I suspect the rating for the plug I was using was well below this; I've seen some that are only rated for 60 W. 

I use one of these plugs to run power to my laptop, another to feed the mount, and a third to power the rest--CCD camera cooling, dew preventer, and USB devices. The total of all these rarely approaches 50 W and is typically more like 25 W, with a little going to the mount and the rest pretty much evenly split between the laptop and camera plugs. Although I've never had an issue with the plugs during imaging this current limitation is something to keep in mind if I ever change equipment. 

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At first glance this Astromania dew preventer looks like a great deal. A 10-inch strap with on-off switch and easily adjustable power control. And the connections are compatible with common 12 V power sockets. What more could you want for a mere $20?

From that buildup you can probably guess it was not quite a great deal. It was a pretty bad one, really.

I connected it to my primary power box and tried it out. I started with the toggle switch off and the power control rotated to the off position. My power box reported 0 W, 0 A. Good. Then I flipped the toggle on. Immediately the Current rose to 2.1 A and the strap started to warm up. In fact, it got quite hot: too hot to wrap around a cameral lens without risking damage. Obviously the controller was somehow defective. With the Controller at it's full-on setting the current was 2.4 A. Were I not a Vine reviewer, I would have returned this immediately. 

But there was another problem, the strap itself. Most straps are very flexible and have no problem conforming to the cylindrical shape of optics. This one won't do that. The plastic lining of the strap is thick and very stiff, and even working it for a while by hand didn't get it to wrap around a 135 mm lens without a few big gaps.

So it was a complete fail and got one of my rare 1-star reviews. Setting aside the problem with the strap the only way this would function is if you could control the current with some other device. And you would want to first make sure the strap connecter would be compatible with your device's strap socket. (It couldn't work with my Pegasus Powerbox or any of my other manual Kendrick controllers, for example. Yes, you could make an adapter for this, with a 5.1x2.5x3 socket on one end and an RCAphono plug on the other. But why bother.) 

Poor Weather & Caregiving: Renewing my Science Fiction Reading; The Tariffs at Work: Rokinon 135mm f/2 Lens Price Update:

Note that this post has little to do with astronomy or astrophotography, so if that's your only interest save yourself some time and move along 😉 

I've been astro-inactive for a while. There haven't been many opportunities for imaging; spring of 2025 in Minnesota has been cold and cloudy at night and sporting occasional snowfalls that recoat the ground. More important is that my wife had knee replacement surgery near the end of March; I've been home acting as her caregiver until she regains her mobility so even if the weather had been cooperative I really couldn't have be going out all night for imaging sessions.

What I've been doing instead is taking advantage of waiting room time by reading recent science-fiction novels. Given my age it's hardly a surprise that most of my sci-fi reading in the past has been of Golden Age authors (Asimov, Heinlein, and Clarke) with some of the 1960s and 70s anthologies of other authors mixed in. Larry Niven features large in these because I like hard sci-fi. I'm not entirely stuck in the past, though. I've read most of Ursula Le Guin's novels, much of Connie Willis's work, and several books by David Brin. And yes, even all three Three-Body Problem novels (more or less).

For My wife's post-op month I decided it was time to see what current sci-fi writers are creating. I decided the Hugo Awards would serve as a good guide and started reading my way through the last decade of winning novels. I hesitated at first given that the Hugos include fantasy but decided blending in some "soft" fiction would be good way to grow out of the hard sci-fi rut I was in.

Here are the first two weeks of intensive page turning summarized in capsule reviews, with a few notes for people who don't want to read certain types of content. The year shown is that of the associated Hugo award.

2024 Some Desperate Glory, by Emily Tesh.

This is the story of a woman born and raised on an asteroid fitted out as a militarized stronghold. It's the last, best hope of humanity to resist the conquest of the Majo, a collection of alien species slowly expanding its influence through the galaxy. 

Tesh writes in a way that challenges you to keep up with the story; her style reminded me of Le Guin's in The Lathe of Heaven. While some reviewers semi-dismissively lump the story into the "space opera" category, I think it has some significant things to say about both technology and humanity. The plot leaned a little too much on the deus ex machina trope, but the pacing kept me from being overly bothered.

Content Notes: AS, SC and a whole lot of violence.

2023 Nettle & Bone, by Ursula Vernon

Characterized as a dark fairy tale, this is pure fantasy with kingdoms, princesses, and spell-casting godmothers. It reads as an adult, grittier take on childhood fantasies. I had a little trouble with what seemed like a sluggish start, but once the author started adding supporting characters the pacing improved greatly, becoming a mix of humor and drama.

And then there's the scene in the Goblin Market, which alone is worth the price of the book.

2020 A Memory Called Empire and 2022 A Desolation Called Peace, both by Arkady Martine.

At one level these explore the ramifications of a technology that permits the transfer of knowledge, experience, and to some extent personality from one person to another. (The method here is strictly technological and not biological as with the symbionts of Star Trek.) The focus is on a woman thrown into the role of ambassador to a galactic empire. She's only somewhat prepared for what happens, and part of the fun and terror is her having to cope with an alien (albeit human) culture. The author's world-building is based on real past human empires and is fascinating to see unfold.  

Fans of Babylon 5 may wonder if the author intentionally borrowed from that TV series. The protagonist comes from a large, rotating space station (some of the descriptions could fit the Babylon 5 station). There are jump gates that permit movement through the empire and the empire itself resembles what the Centauri might have become if not checked by other spacefaring races and their own lapse into decadence. There's even an aged, ailing Emperor with intrigue between those maneuvering to be his successor. Oh, and let's not forget the mysterious attacks by large, shimmering black, and cloaked vessels from far jumpgates. They sometimes scream as they depart.

I don't mean any of that as complaint. If you want an extensive empire with far-flung possessions spanning tens of parsecs, you need to explain some way of getting around that old wet blanket Einstein. Jumpgates, wormholes, warp drives, hyperspace, folded space, infinite improbability drives, or whatever, numerous authors have already explored the territory. As long as you don't steal technology by its proper name (Sheewash Drive, for example) you're fine. The story is more important than the mundane tech bits.

The quality of the writing is what matters, and in these two novels it more than compensates. 

Content Notes: AS, SC

2021 Network Effect, by Martha Wells

This is the fifth entry (and first novel) in a series call the Murderbot Diaries. I've only read the  introductory novella (2017's All Sytems Red) , and it was a fast, breezy, and intriguing read. Network Effect is a full-length novel and it's recommended that one read everything leading up to it before taking the plunge. So I'm making the collection a birthday gift suggestion and it might be my reading material for this summer's Northern Nights Star Fest (if I'm not stuck at home when her other knee is replaced!)

Content Notes: Lots of violence, as you might expect when the protagonist is named Murderbot. 

2019 The Calculating Stars, by Mary Robinette Kowal

It's no spoiler to say this is an alternative history novel. If you don't mind reading about the many injustices inflicted on 1950s women and minorities (both religious and racial) this is an enjoyable throwback novel that in many ways is very remindful of the 2016 book and movie Hidden Figures.

The story combines both hard science and social commentary. The writing is adequate, occasionally rising to excellent -- particularly at the conclusion. This is the first book in a series of three.

My suspension of disbelief was mildly tested by what I felt like was an overstatement of what the described technology was capable of doing.

2016 The Fifth Season, 2017 The Obelisk Gate, and 2018 The Stone Sky, all by N. K. Jemisin

Yes, an unprecedented three consecutive Hugo awards!

These are world-building carried to an amazing extreme. At this time I'm in the third book and would love to explain what's happening, but my understanding of it is a work in progress. Riding along with the characters as they try to understand what's happening to their world is a big part of the fun. 

The story unfolds in a rather unconventional manner, but that's in keeping with the plot. I'd say more, but it's almost impossible to do so without resorting to spoilers.

Content Notes: Quite a bit of violence, much of it like something from a very dark version of Frozen. 

2015 The Three-Body Problem, by Cixin Liu (translated by Ken Liu) 

This wasn't read during this month's blitz, but I'm including it to round out the decade. This introduces a very alien culture and instantiates the Dark Forest answer to the Fermi Paradox. I enjoyed this book, but found the subsequent two novels (The Dark Forest and Death's End) so unreadable that I hopped rapidly through them to reduce the pain.

Content Notes: Mind-numbing content (mainly in book three and the second half of book two.) 

Content Notes for those to whom these things are important:

AS: Alternative sexualities. I found these were important to the plots, but you may feel differently.

SC: Non-gratuitous Sexual Content. Interestingly, it was The Calculating Stars that had the most explicit sex, suggesting that the author was making the story compatible with readers of romance novels. The only sex scene that felt a little out of place was in A Desolation Called Peace. (And no, I'm not going to tell you what chapter it was in so you can just skip right to it.)

All the stories involve spoken vulgarities, and most feature violence of varying degree.

If you're someone who resents anything that seems the least bit "woke," I'd suggest you stick to the Hugo winners from several decades past. Better yet, focus on the Retro Hugo Awards that recognize works from 1939 to 1954. Two of my favorite stories are there, Asimov's 1951 winner Pebble in the Sky (the first sci-fi I read) and Clarke's 1954 nominee Childhood's End. The latter is an amazing story, and it only lost the award because it was up against the equally amazing and iconic Fahrenheit 451 by Bradbury.

Just so you know, my wife's recovery is coming along wonderfully, and I truly hope that my next post will include some astrophotography news. 

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Tariff Watch:

[UPDATED : On April 5 the B&H Rokinon 135mm lens Canon EF version price rose to $479, $30 up from what it was on April 4. It's now up $110 from it's pre-tariff price in early February of $368. That's an increase of 30%. 

But hold on! The price dropped back down to $449 on April 6!  Was yesterday's price hike an error, or a preview of what happens when they need to restock? Wait and see!

TILT!

Yes, it's that enemy of flat fields: tilt in the optical train. 

Recall -- or don't, since I'm going to repeat the information anyway -- that my first choice for imaging the Polaris-area integrated flux nebulae was an old Tamron 135 mm f/2.5 lens that stopped down to f/4 is quite a nice lens. Second choice is to use my FSQ-106 with a 0.73X focal reducer that gives me a nice wide field. The FSQ is wildly higher in quality than the Tamron, but the only time I've imaged with the focal reducer it produced results that barely adequate: stars were noticeably elongated on one side of the image. 

I'll need to use the FSQ + focal reducer if for some reason the Tamron proves to be problematic. That means it's time to chase down the tilt problem and get it fixed.

What dawned on me recently was that there was enough back focus to allow me to use the tilt plate that came with the ASI 2600 camera I use for imaging. I had removed the plate to make the ASI compatible with my DSLR. The fact is that the ASI has largely made the DSLR superfluous; I'm  unlikely to image with it again. The tilt plate can therefore come out of storage and get back into action. Here's the present situation:

The configuration of interest here is the bottommost one. The reducer requires that the camera sensor be at a very specific distance from it: 72.2 mm. Currently there's a 12 mm M42 spacer in the optical train. Replace that with the tilt plate and a 7 mm spacer and it's all good (aside from some very thin spacers). 

Now, how to use the tilt plate? Let's start by verifying that it's the optical train and not the sensor that's out of whack. To do that correctly, I'd need to rotate the camera relative to the optical train and see if the effects of the tilt moved with it. I'm going to cheat a little and assume that if the field is flat for the native imaging mode (f/5) the sensor is fine.

Here's the ASTAP measurement of tilt in a single luminance image taken with native mode (f/5):

ASTAP report of field flatness for FSQ-106 & ATI 2600

So you're probably asking, "what the heck is that?" The numbers next to the yellow lines are the area-averaged half flux diameter (HFD) of the stars. The HFDs essentially measure how pinpoint the stars are, and they can be affected by focus quality, seeing, and aberration and tilt problems. A perfect telescope with perfect optics and perfect seeing would have very small numbers in this diagram.

Tilt will introduce variations in HFD that are in the direction of tilt. So how does one assess these numbers? ASTAP does that for you. If you look along the bottom edge of the above picture you'll see it assesses the tilt at 6%, which it judges to be "almost none". Great! This suggests that the native optics are adequately tilt-less--and by extension that the sensor is reasonably perpendicular to the optical axis.

Now here's the ASTAP analysis for a luminance frame taken using the reducer (f/3.65):

Same as above, but with the focal reducer

ASTAP says the tilt is 19% (moderate). It also confirms my eyeball judgement that the tilt is largely oriented along the long axis of the sensor. 

(Yes, you could deal with some star elongation in post-processing, but isn't it better to not have to do that? This brings us back the the first defense against tilt, a tilt plate.)

The ZWO tilt plate works using three adjustment screws arranged in an equilateral triangle, much like the tilt screws for adjusting a small Newtonian objective mirror. What I'll do is to orient the plate so that one of the adjustment screws is in the direction of the tilt, like so:

Orientation of ZWO tilt plate: blue arrow = tilt direction, red dots = adjustment screws

This way the adjustment screw at that left vertex becomes the primary one to adjust. Note that ASTAP has an option to provide a 3-point analysis which may be easier to interpret in some cases.

The process of correction is basically repeating the sequence of imaging, analyzing, and adjusting. It's another new skill to learn and put to use, which is good. There doesn't seem to be much to it; I'll let you know how it goes.

Unfortunately this won't work for the 135 lens; it has no spacers to swap out for the tilt plate. Should I find it needs correction, I'll probably use these things. I might get that and see if it's all I need for correcting the focal reducer tilt, too. If these shims work for that it would eliminate the need for a tilt plate and make it easier to change from one configuration to another. 

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At least it's March now. A few inches of snow is coming in the next day or so, just because it can. Almost time to make my reservations at Lac qui Parle!

[Added 5 March, it was more like 9 inches.]