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.