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.