Processing (and Color Mixing) Really Matters!

I took what I thought was pretty good LRGBHSO data for the Eagle Nebula. The LRGB combination looks OK, 

but I completely struggled with adding in the narrowband data. No matter what I did, I didn’t seem to be able to add in the rich detail from the Hα without losing the rich color from the LRGB. Here's the Hα:

The Hubble palette attempt turned out OK as well, but in retrospect, I think the Hα is probably stretched a bit too hard so I may go back and try a redo on the SHO version. It is clear there is a lot of detail in the Hα.

I’ve tried a lot of different variations for processing this year’s narrowband data for M16. The final colors are very sensitive to what I do in early steps of the processing. Obviously the amount of stretching applied to the various channels matters a lot. I have a version I like a lot that is mostly in golds, but ultimately I think the best rendition is this one where I try to make the dark end of the histogram similar for all three color channels and the OIII still shows up as blue. This is a really nice target for SHO because there is significant emission at each of the three wavelengths. RGB stars were extracted from my RGB image, shrunk a bit with Carboni’s “make stars smaller”, then added using screen mode in Photoshop. Several rounds of “less crunchy more fuzzy” were applied, with the effects masked out for the Pillars and other places where there is detail I didn’t want to lose.

But the point I really want to make is best illustrated by my various attempts to blend the narrowband data into the LRGB. For example, in this image I tried to use both Hα and OIII blended with the LRGB. I had thought that OIII goes best with B, but I think a stronger argument could be made for blending OIII with G. Be that as it may, this just didn’t turn out as well as I wanted although it was better than what I had gotten to that point.

Disclaimer: this image uses the same data as my last two posted images (in fact it combines the data from them). This is an attempt to get a “truer” color version of M16 but including the contrast and depth you get with narrowband filters. I used a combination of Hα and L for the L layer, Hα and R for the R layer, G only for the G layer, and B+OIII for the B layer. Each of the 4 layers was processed separately and each was stretched roughly the same amount. Combination was done using StarTools’ LRGB module. I did some slight tweaking in Photoshop using Levels, Hue and Saturation, and Vibrance but otherwise didn’t process much after combining the layers. This is not stretched nearly as hard as the SHO image was, and I think this version turned out better than my straight-up SHO. The gentler approach wins.

Then, while working on another image (M17, the Omega (or Swan or Lobster) Nebula), I remembered the Starizona web site (https://starizona.com/tutorial/using-an-h-alpha-image-as-a-luminance-channel/) has a tutorial on doing HαRRGB combinations and decided to review it. Their approach involves mixing (mostly) Hα with R and using that combination for the R layer and for L (method 1) or using the Hα by itself for L (but at ~75% opacity) with the HαRGB contributing the color (method 2). With my data, these approaches gave results I think are far superior to what I got in my feeble attempts to figure out the mixing:

I don’t usually repost the same data under a new heading, but after seeing how the Starizona HαRRGB methods worked on M17 I had to go back and try them on M16. These data look (in my opinion) dramatically better when processed using the Starizona methods so I’m going to break my own rule. I used my RGB image posted previously (https://astrob.in/352634/B/), added Hα to the R, and used either Hα+R (method 1) or Hα alone (method 2) for luminance. I tweaked the curves as suggested on the Starizona site, boosted the saturation a little, and used Carboni’s layer-masked “less crunchy more fuzzy” to make the stars less harsh. I think these look a lot better than what I posted earlier. This time I think I prefer the method 2 image for the detail it reveals in the nebulosity.

Date: 15-20 Jun 2018

Subject: M16, Eagle or Star Queen Nebula

Scope: AT8IN+High Point Scientific Coma Corrector

Filters: ZWO 31 mm diameter unmounted L, R, G, B, Hα

Mount: EQ-6 (EQMOD 2.000j)+PEC

Guiding: Orion Thin Off-axis Guider + DSI IIc +PHD 2.6.5 (Win 10 ASCOM)

Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21 

Acquisition: Sequence Generator Pro 3.0.2.91

Exposure: 51x180 L, 20x180 R, 20x180 G, 20x180 B, 48x300 Hα

Stacking: Deep Sky Stacker 4.1.1 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5.

Processing: StarTools 1.4.332: Combined R, G, and B in StarTools. Binned 2x2, cropped, wiped, developed, HDR, color, deconvolution. Stopped tracking to smooth. Binned L 2x2, cropped, no wipe, and developed followed by HDR. Deconvolution followed by untrack smoothing. Combined L with RGB in Photoshop. Used some layer-masked saturation adjustments, both in the master and in the red channel, to try and retain the red color. A little of Carboni’s Astronomy Tools’ increase star color followed by less crunchy more fuzzy. Green cast in stars removed using StarTools’ “Cap Green to Yellow”. Also some different choices in Curves for the luminance and RGB layers to better bring out the reds in the emission nebula. Added Hα as described above.

In Honor of Alan L. Bean, 4th Man to Walk on the Moon

I sadly note the passing of another moonwalker, Alan Bean (Apollo 12). Now there are only 4 men left alive who have walked on another world. So I’m posting in honor of Alan Bean and in gratitude for the inspiration his accomplishments have been to me ever since I was very young. I have very much enjoyed his painting, which is from an incredibly unique perspective. It would be just after dawn at the Apollo 12 landing site in this image.  I am grateful to have lived in a time when mankind has reached so far, but I think one of the great tragedies of my generation is that in many ways we have not pressed forward as we might have.  Very soon there will be no one left alive who has walked on another world, and that will be a shame.

I took this image not originally intending to do anything with it; while I was waiting for the sky to get dark I was basically just fooling around wanting to see how the ASI1600MM-cool would perform and what kind of frame rates I could get. I was extremely impressed with how easy the finding was using an automated mount connected to Cartes du Ciel, and how easy the capture was using SharpCap, which interfaces beautifully with my camera, mount, and focuser. I continued having fun with the processing, attempting to remember and relearn what I know about lunar/planetary imaging and processing. PIPP and Autostakkert still work great (although I wasn’t able to get Registax to run after very limited effort). All of this makes we want to try this camera in lunar/planetary mode with a Barlow lens and more careful focusing, and using filters to get color when appropriate. I haven’t done much of that kind of imaging in a long time believing that my gear isn’t well suited to it.

The image itself is reasonably sharp given how little effort I spent capturing it and the relatively short focal length I used. Tycho shows up well, as does Copernicus. I was surprised to see how bright the little crater near Mare Crisium is; I believe it is Proclus, which is reported to have very high albedo.

Date: 25 May 2018

Subject: the Moon

Scope:  AT8IN+High Point Scientific Coma Corrector (~900 mm FL)

Mount: Skywatcher EQ-6

Guiding: none

Camera: ZWO ASI1600MM-cool at gain 0, -20 °C

Acquisition: SharpCap 3.1.1586.0

Exposure: 1000 frames SER captured at about 9 fps

Stacking: PIPP + Autostakkert, best 50%, automatic alignpoints, sharpened; Astronomy Tools Astroframe.

A Year's Experience with the ZWO ASI1600MM-Cool and a Year's Progress

I bought my ZWO ASI1600MM-Cool a year ago, and after using it for a year I still love this camera. It produces far better images than I could ever get with my old Meade DSI IIc. Some of this performance is no doubt because of the smaller pixels and the fact that it's a monochrome camera so doesn't suffer from the limitations imposed by a Bayer matrix. It also true that this better performance comes at a cost; not just the higher cost of the camera, but also in much greater effort required for processing the data (at least in my hands). The much higher number of pixels alone means that processing time is much longer (I'd estimate a factor of 3-5 times at least) and data storage requirements are much greater (more than a factor of 30--my primary drive is filling up fast!). In addition, it has been a real adventure (and actually a lot of fun) learning how to do LRGB, SHO, HSO, and various other combinations to produce color images. I've still got a lot to learn about that!

I've now used this camera with my AT8IN 8-inch imaging Newtonian, with my Orion ST-80 very-non-apochromatic refractor, and with an old Tamron 135 mm camera lens bought for $15 on e-Bay, and it has done a good job with each. The much larger imaging area does mean that the optical flaws in my systems are much more apparent than they were with the DSI IIc; its tiny sensor only sampled the nearly flawless center of the image plane, whereas the ASI1600MM-Cool finds lots of flaws out near the edges of the field of view and I see plenty of effects from vignetting that I never saw before. I've got one dust mote on the sensor that I either have to correct with flats or correct in software, but I've pretty much figured out how to do that.

I've experimented with various gain/offset settings, and find myself gravitating back toward the "default" unity gain (-139) offset 21. I really don't have a scientific reason for this. It's just what I've found most comfortable with the exposure times and dynamic range expectations I have. I think higher gain combined with shorter exposures is an approach with a lot of promise, as it seems like it would allow better statistical treatment and would minimize any frame-to-frame drift from differential flexure (I see a lot when using my finder/guider with the Tamron lens, and even see some when using an off-axis guider). A future goal is to get a bit more scientific with these experiments.

The only persistent problem I've had with this camera appears to be in the USB-3 cable connecting the camera to a hub located at the telescope mount. Occasionally the connection to the camera and filter wheel drops, with the result that the next attempt at downloading an image hangs. I've had quite a few sessions end prematurely because of this. Often it happens while doing a meridian flip or right after a filter change. I'm sure it's not the hub or the USB cable back to my living room, because the guide camera is also on that same hub and never has problems. When I originally set up the ASI camera I noticed it only seemed to work well with the cable that shipped with it, so it seems to be a bit picky about the cable. I might try getting another cable to see if it makes a difference. Usually, jiggling the cable and doing an unplug/replug fixes the problem.

All of that said, I've learned a lot over the last year. As evidence, I offer the following two images. The first was done a year ago, and was the first time I had used the ASI1600MM-Cool with the Tamron 135 mm lens. Because it was a "first time" in many ways, maybe this isn't exactly a fair comparison. At any rate, I was delighted with the image at the time, because there was no way I could have done anything like that with my prior setup.

This image was a first in many ways. It was a first attempt at this large, dim, difficult target. It was the first use of the Tamron 135 mm f/2.8 lens I bought for $15 on e-Bay. It was my first try at using high gain with the ASI1600MM-Cool, and it was first light for the Tamron 135+ASI1600MM-Cool combination. I didn’t get any blue data (the neighbor’s darn tree got in the way again), so I cheated: I used the Hα data both for luminance and for R, and I put the R data in the B channel. All things considered, it could have turned out worse. I had to process the heck out of this to get a result that was anywhere near reasonable. The supernova is reported to have gone off 40,000 years ago!

Date: 7 Jan 2017

Subject: Sh2-240 (Simeis 147) Spaghetti Nebula supernova remnant

Scope: Tamron 135 mm f/2.8 lens

Filters: ZWO 31 mm RG, ZWO 7nm Hα

Mount: EQ-6 (EQMOD)+PEC

Guiding: Finder/Guider+DSI IIc+PHD 2.6.2.4 (Win 10 ASCOM)

Camera: ASI1600MM-Cool, -20 °C, acquired Hα 1x1 RG 2x2, Gain 300 Offset 50 

Acquisition: Sequence Generator Pro 2.6.0.1

Exposure: 80x180 s Hα, 55x45 s R, G

Stacking: Neb 4.1.2, flats & darks, trans+rot align, Nebulosity 1.5σ stack.

Processing: too extensive to detail.

The second image is my most recent, just finished today. In the last year I've learned a better way to mount the camera on the lens, and I've built, tested, and used an automated stepper-motor-based focuser (based on Robert Brown's designs and using his software) for the lens. I've learned to do bicolor combinations and have benefitted greatly from Annie's Astro Actions for Photoshop, which make this easy. I've gotten better at picking good stars for doing alignment and stacking in Nebulosity (I tend to use dimmer stars that have good shapes, and I always magnify the image when I choose them, avoiding ambiguity in which star is picked). I'm trying to be a bit more subtle in my processing, so my images probably are not as stark from trying so hard to pick up the really dim stuff. To me this newest image is far better than the one from a year ago. One of the things I really love about astrophotography is that it's easy to see progress!

One motivation for this image was to compare with the image I took a year ago, which was the first using the Tamron 135 mm lens; I wanted to see how much my technique and experience had changed over the last year. The new image suggests these have changed a lot. I had intended this to be HSO/SHO, but the session failed while trying to focus the SII filter (which was the last in the sequence) long after I had gone to bed, so it ended up being only bicolor. It looks like the weather is turning stormy at last (winter is coming pretty late this year in Utah) so I’m going with the data I have rather than wait for more clear skies. These data were tough to process because this target is quite dim, hence the original data required very extensive stretching and were consequently pretty noisy. Nearly all the structure shows up only in Hα (only the barest hint of the filaments in OIII), though I’m curious whether anything would have been visible in SII. I continue to have trouble with my Tamron 135 flats (the current ones overcorrect), so I ended up not using them and just let StarTools’ Wipe vignetting module handle things. I went back and forth a few times about how dark to make the background, and ended up leaving it fairly dark. I understand this nebula is thought to be a supernova remnant. The structure in the filaments is amazing—it looks to me more like a wad of fine spun gold with the color choices in this image, rather than spaghetti—leading me to wonder what caused it. Most likely it was just random turbulence at the time of the supernova explosion, but it is fun to speculate that maybe it was somewhat shaped by a planetary system around the star, destroyed at the time but imprinted on the remnants (now that we know that most stars do have orbiting planets). Of course I have no evidence for such romantic speculation!

Date: 19 Dec  2017

Subject: Sh2-240 (Simeis 147), Spaghetti Nebula

Scope: Tamron 135 mm f/2.8 lens stopped to f/4

Filters: ZWO 31 mm diameter unmounted Hα, OIII (7 nm bandpass)

Mount: EQ-6 (EQMOD 2.000j)+PEC

Guiding: Orion 9x50 Finder/Guider + DSI IIc +PHD 2.6.4.5 (Win 10 ASCOM) using predictive PEC algorithm

Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21 

Acquisition: Sequence Generator Pro 3.0.0.4

Exposure: 40x300 Hα, 36x300 OIII

Stacking: Neb 4.1.6, darks only, trans+rot align, Nebulosity 1.5σ stack and align.

Processing: StarTools 1.4.328: Used StarTools’ “Wipe” module to correct for vignetting, then stretched and deconvoluted each channel separately in StarTools. Aligned the processed layers in Nebulosity then combined in Photoshop using Annie’s Astro Actions’ HO Bicolor module. Multiple rounds of Photoshop Curves and Levels, combined with several rounds of Carboni’s Make Stars Smaller, then Deep Space and Space Noise Reduction and a few rounds of Less Crunchy More Fuzzy. AstroFrame.

2 Minutes, 17 Seconds

11:09 AM

Ever since reading about them as an elementary school student, I have longed to see a total solar eclipse. It has been a “bucket list” item. At long last, I have finally checked that one off. On Sun. 20 Aug I traveled with my wife Denise, my son Brent and my son-in-law Eric Mansfield to Rexburg, Idaho to view the 21 Aug 2017 “Great American Solar Eclipse” in totality. We had originally planned to go in the afternoon, after church, but I guess I got over-anxious about forecasts of huge crowds and traffic problems. The last thing I wanted was to be stuck in a traffic jam on I-15 somewhere south of the zone of totality, so we left around 7:30 AM and drove up to Idaho Falls, just a few miles south of the zone, where we went to church. We then drove on up into Rexburg, more or less to the center of the zone. We saw no heavy traffic at all. We had a reservation to camp in Riverside Park in Rexburg, where they had taken a large grassy area and partitioned it into hundreds of tent sites across a little river from a parking lot, which was entered by permit. I had bought this from a guy online who couldn’t go, so I couldn’t help but worry a little that he might have sold it more than once, but those worries were completely unfounded; all was perfect. 

11:14 AM

There were probably a thousand people camped in the park. In the parking lot they had food trucks and lots of booths selling various memorabilia; the sister missionaries from the Mormon Church (mine) were there with a family history booth. I’d say most of the people who were there, who were mostly families, were from Utah, but visitors were clearly there from all over the world. I bought a T-shirt. A few people had telescopes and were practicing projecting images on tent sides, and one guy had what looked like a 12” Dobsonian. I anxiously watched my weather apps (Weather Channel, ICSC, & Observer Pro), worrying we might get clouded out right at totality, and Sunday afternoon it was looking like we were going to have some clouds at the crucial moment and were certainly going to have some overnight. Sure enough, around sunset it clouded up pretty well, so the Dobsonian guy didn’t get to use his scope.

My bio-alarm (a full bladder) woke me around 6:15 Monday morning to a perfectly clear sky, which remained through the eclipse and beyond, so that worry was also unfounded. We packed up our stuff and drove over to the home of my college friend, Steve Ott, who is on the faculty of BYU-Idaho. Again, there were worries that the whole town of Rexburg would gridlock with visitors, but that did not happen. I would say the city was extremely well prepared for the eclipse and probably got fewer visitors than expected. The predicted gridlock in Rexburg didn’t happen. Cell phone service was not interrupted, although the traffic cameras did become inaccessible. So all in all, the infrastructure held up pretty well. At the Ott’s I stayed busy trying to make a solar filter for my iPhone/2x telephoto attachment (didn’t work well at all; too many nasty internal reflections and no ability to set the phone camera’s exposure times short enough) and setting up my point-and-shoot to try and image totality. 

11:22 AM

The eclipse started about 10:15 AM, with a little nick appearing in the side of the sun. We had lots of pairs of eclipse glasses, and I had a pair of solar binoculars from Celestron. Eric had made filters for his binoculars using some Baader astro solar film I had left over from making filters for my scopes for the transit of Venus. We also hastily assembled a pinhole camera and Steve had a small (maybe 50 mm) old telescope with a somewhat dangerous “solar” filter that screws onto the eyepiece. The eclipse glasses gave a nice sharp view and were easy to use, showing the Sun in an orange color, but the binoculars gave a much closer if whiter, less colorful, view. There was a nice line of sunspots across roughly the center of the Sun that allowed us to mark the progress of the Moon across the Sun. These were easily visible through the binoculars. I liked the simplicity and sharp view afforded by the eclipse glasses. One thing I noticed right away that was different about this total eclipse vs. the partial eclipses I’ve seen before was the symmetry: the Moon’s motion across the Sun was centered right on a diameter. I was a little disappointed with the pinhole camera because its image was small and not particularly bright. What did not disappoint, and one of the highlights of the experience, was looking at light coming through the trees in Steve’s front yard. I got lots of pictures of this, and it was easy to follow the course of the eclipse by looking at how deep the crescents were.

11:23 AM

I had read that you should look for diffraction fringes (“shadow bands”) moving across the ground just before and after totality, so we did and we saw them; a conveniently located white car, belonging to one of Steve’s family members, provided the perfect screen to view the shadow bands. These were spaced maybe an inch apart, they moved rapidly, and were very faint. One of our group said it looked like mirage ripples or like seeing light through rippling water and I think that’s a good comparison, although it was dimmer than what you see through water. 

I also wondered if we would be able to see the Moon’s shadow approaching. Just before totality I looked out to the west-northwest, where we had previously determined the shadow would come, and sure enough I saw a shaft of darkness coming down from space. It was impressive. 

11:25 AM

Through most of the eclipse you couldn’t tell any difference in the brightness of the sunlight, but for perhaps the last 5 minutes prior to and after totality the light was obviously dimmer and the temperature was also noticeably cooler. Some of our group saw the street lights coming on, but I didn’t because my attention was elsewhere.

11:37 AM

Then came totality (11:33 AM), with cheering from all over town and lots from me. It was about as dark as an hour or so after sunset, dark enough that the brighter stars and Venus were easily visible. And the corona, which was a beautiful silvery white and full of easily-seen filaments and asymmetric, was naked-eye visible out to 4-5 solar diameters. I fumbled to get this in the field of view of my point-and-shoot camera and hit the exposure button with the intention of taking continuous 5-sec exposures at maximum zoom through the 2 min 17 sec period of totality. I hit the start button without starting the program, so I got nothing photographically from that effort. In retrospect, 5-sec exposures would have been far too long anyway. I did have my 70 mm binoculars ready and prefocused, so I got them on the totally eclipsed sun and was rewarded with a beautiful and somewhat unexpected view of several large prominences along the top and trailing side of the eclipsed sun. These were bright orange to contrast with the silvery-white corona. Steve Ott had a phone app running that counted down to the Sun's emergence from behind the Moon and also mentioned out loud what to look for; this was very helpful. This allowed me to get the binoculars down in time. We got an awesome “diamond ring”/Bailey’s beads effect as totality ended. Pictures do not do this justice as they can’t capture the huge dynamic range between the darkness of the Moon’s disk and the actinic brightness of the Sun coming through Lunar topography. The time of totality was unearthly, beautiful, and over way too quick.

It got light and warmed up, and we saw the diffraction ripples again. Everything happened in reverse from there. I got some pictures of very narrow shadow crescents. I hung on to the bitter end, trying to see 4th contact. I lost the Moon from the Sun’s edge about 20 seconds before the app said the eclipse ended.

We decided to drive down to Ririe, Idaho, where Denise’s dad grew up, and also visited the Ririe-Shelton cemetery where her grandparents are buried. All the entrances were locked up to prevent people from driving in, but we were able to walk in. We saw lots of this: public parking lots and the like were blocked all over the zone of totality, presumably to force people to rent spots from the farmers who were gouging outrageous prices. 

11:42 AM

We then started heading south along back roads, which were all jammed. We (and probably everyone else) were using Google Maps to try and avoid the mess, and just kept getting into the mess. This was the worst traffic jam I have ever experienced in my life. Idaho Falls was a congested chaos, with many freeway on ramps closed. We eventually got on I-15 and moved at about 5 miles per hour average. Things finally lightened up a little south of Pocatello, but then jammed up again north of Tremonton, Utah and stayed heavy until Ogden. We didn’t really get to full speed until the Salt Lake Valley. While it took about 4 hours to drive up to Rexburg, we needed more than 9 to come home. The Eclipse Expedition was an adventure, and was completely worth it. Now I want to do it again!

As I continue to reflect on the experience, this was among the most impressive public sights I have ever seen, up there with watching men walk on the Moon (on TV, of course) and witnessing a space shuttle launch from close enough that I not only saw it, but heard and felt it. 

12:21 PM

And I can’t help mentioning a spiritual insight that came from watching the eclipse, which after all was a very spiritual experience for me. We read in Mormon scripture about how a mortal human cannot behold God with the natural eyes. It occurred to me that the Sun is a good analogy to this. We can’t look at it unaided for more than an instant without severely damaging our eyes (you’d better have those eclipse glasses or something equally good!). Because of this, we go through most of life not comprehending how truly grand our star is. Seeing the eclipse gave me a whole new perspective on the Sun; it’s not just a brightly glowing disk, but its corona and magnetic field extend way further into space in ways we can’t normally see and of which we are not normally aware. Of course I knew all this and more before, but seeing it gives it far deeper impact and meaning. In the same way, we mortal humans cannot bear to look directly at God. A finite mortal mind cannot perceive or indeed even conceive of a superintelligent God, yet at the same time, just as we can understand that our Sun nurtures all life on Earth, we can understand that we are all God’s children and that he loves us enough that he sent his Son in loving, atoning sacrifice for all of us. I’m grateful to have this knowledge.

1:59 PM (post eclipse)

Automated Focusing of the Tamron 135 mm f/2.8 Lens

My second-iteration MyFocuser Pro control box

I thought I’d start writing up my experience building a motorized focuser for the Tamron 135 mm f/2.8 lens. After using the Tamron 135 mm f/2.8 lens a time or two, it has quickly become apparent that the various filters I’m using are not parfocal, which maybe should have been obvious given that the lens uses refractive optics and refraction is wavelength-dependent. Therefore, if I want to get good images with this lens I’m going to need to refocus at least every time I make a filter change. That would badly interfere with sleep. I recalled that Robert Brown’s do-it-yourself MyFocuser Pro project includes description of a setup for using  his Arduino Nano-controlled stepper motor focuser on a camera lens using a belt-pulley system to move the lens. After a little investigation, I decided to build a second MyFocuser Pro system to implement motorized focusing with the Tamron 135 mm f/2.8 lens. Experience with my original MyFocuser Pro has shown me I don’t use either the LCD display or the manual buttons, and a little calculation showed that with 1/32 stepping I don’t need the more expensive planetary gear stepped-down stepper motor. This meant I could build the minimal MyFocuser Pro and use it on the inexpensive NEMA 17 stepper motor and expect reasonable performance. 

I ordered the parts, waited for the slow boat across the Pacific to arrive, then assembled them. After a little Googling I realized I didn’t need to buy a special LED to run at 12 V for the “power on” indicator; rather, using two 1-kΩ resistors I already had on hand, wired in parallel, would give me the 500 Ω resistance needed to provide proper current limitation to a regular cheap LED. After initially building a board that had the transmit terminal of the Arduino shorted to +5 V (which of course could not talk to my computer), I found and cut the shorted trace, loaded the minimal MyFocuser Pro software, and got the motor moving. 

T-adapter attached to Tamron lens, with
toothpicks holding the aperture open.

I bought some toothed pulleys with a long length of toothed belt originally intended for do-it-yourself 3D printer assembly. The ends of the belt are glued together to make a loop of the proper size. I tried to get the belt length right by trial and error and found considerable tension was needed to get it to adjust the lens focus without slipping. 

Toothed belt glued to lens focusing ring.

Camera, filter wheel, lens, and focus motor assembled.

When I finally got this rig on the sky, I found the autofocusing routines in Sequence Generator Pro worked quite well with this setup. The attached images show the difference between manually focusing once then never refocusing (in the Spaghetti Nebula image) and using autofocusing every 10 subframes and on filter changes (in the Christmas Tree Cluster/Cone Nebula image). Refocusing helps a lot in my opinion. 

The setup worked pretty well on the first night out, but much more poorly on the second night. That second night I also noticed that I could see the region of stars that were in focus march across my image from bottom right to upper left as I adjusted the focus, strongly suggesting that the optical image plane and the plane of the imaging chip were not parallel. After the session ended I found that the tight belt around the lens had put a sideways force on the lens that pulled apart the glued joint holding the lens to the T-mount ring. No wonder the lens seemed misaligned with the camera; it was! 

I cleaned off all the hot glue I had used before to make the joint, and replaced it with Gorilla Glue Epoxy reinforced  with duct tape (the magical tool of all science), which I hope will hold better. Because I had a lot of toothed belt left over, I decided to try a different way of connecting the stepper motor to the lens. I hot-glued a ring of toothed belt around the focusing ring of the lens. This meshes with the toothed belt from the pulley, making a firm, non-slip connection between the motor and the focusing ring without needing a lot of tension. Initial testing suggests it moves the focus  reproducibly without a lot of backlash or hysteresis. We’ll see what really happens next time I get a chance on the sky (which may be a while, given recent weather; even with a beautifully clear day like today, the forecast says it’s going to cloud up again tonight!).

Image taken without refocusing. The blue channel is not focused as
well as the others.

Automated refocusing using Sequence Generator Pro and the MyFocuser Pro
motor assembly. Notice how much smaller the stars appear.

Resurrecting an Old Camera Lens for Astrophotography, Part 2

Some time ago I decided to try using my old Quantaray zoom lens, once used on a Minolta film camera, for astrophotography. The experiment worked reasonably well, but at f/5.6 at best, the Quantaray lens is fairly slow. In addition, that lens was designed for autofocus use. This presents some problems for astrophotographic applications because moving the focus manually just a little makes a big difference and the manual focus is very sensitive to just a slight touch.  

Tamron 135 mm f/2.8 lens with T-adapter glued to the top

I have seen a number of nice images on Astrobin taken by John Leader using a Tamron Adaptall f/2.8 camera lens (in fact, this is what originally inspired me to try the Quantaray). Seeing a few more images motivated me to look into how much the Tamron lens might cost, and I found that used lenses are available for low cost on e-Bay from time to time. Knowing that Tamron invented the T-mount to allow their lenses to be mounted on a variety of cameras, I assumed the lens would come with T-threads, which fit my astrophotography cameras. I found a Tamron 135 mm f/2.8 lens with a Canon adapter of some sort on e-Bay for $15. Its condition was not specified, but pictures of the lens looked good and the price was so low I figured it was worth a try so I ordered it. When it arrived I found its condition was excellent, but my assumption that I could just pull off the Canon adapter and expose T-threads was ill-founded. I decided I could do something similar to what I had done earlier with the Quantaray, which was to just glue a T-adapter to the back of the lens. I used a hot glue gun and a liberal amount of glue to attach the adapter, then wrapped the joint in black rubber waterproof tape to secure the joint and discourage light leakage. A spring-loaded toggle switch enables the f/stop adjustment, but for my initial experiments I left it free so the lens remains wide open at f/2.8 (later on, I can easily shim the spring-loaded toggle so I can use the f/stop ring to stop down the lens if I want).  The attached picture shows the adapter on the lens.  I got a mounting ring for my ASI1600MM-Cool camera with electronic filter wheel. The mounting ring screws onto a dovetail bar, which also holds a finder/guider so I can put the whole thing on my mount and do autoguided LRGB and narrowband astrophotography. 

Lens, filter wheel, & camera on dovetail bar with guide scope

I chose a very challenging target, Sh2-240, aka Simeis 147, the Spaghetti Nebula, to test the setup.  This target is about 3° in diameter, much larger than I can image with any other optics I have, but it is quite dim and benefits greatly from narrowband filters, especially Hα. Therefore, this target would present a good challenge for this lens. The image was a first in many ways. It was a first attempt at this large, dim, difficult target. It was my first use of the Tamron 135 mm f/2.8 lens. It was my first try at using high gain with the ASI1600MM-Cool (gain set to 300—much greater than unity—and exposures of only 45 sec for LRGB and only 180 sec for Hα), and it was first light for the Tamron  135+ASI1600MM-Cool combination. I didn’t get any blue data (the neighbor’s darn tree got in the way again), so I cheated: I used the Hα data both for luminance and for R, and I put the R data in the B channel. All things considered, it could have turned out worse, and the lens passed with flying colors. It was easy to focus and seemed to stay focused. I won’t say that the stars looked perfect all the way to the edge, but they looked pretty good especially in the region I cropped to for the attached image. I did the cropping primarily so I wouldn't have to deal so much with the extensive vignetting produced by my 31 mm diameter unmounted filters on the ASI1600MM-Cool imaging chip. I had to process the heck out of this to get a result that was anywhere near reasonable. The supernova that produced this remnant is reported to be  about 3000 light years distant and to have gone off 40,000 years ago!

Date: 7 Jan 2017

Subject: Sh2-240 (Simeis 147) Spaghetti Nebula supernova remnant

Scope: Tamron 135 mm f/2.8 lens

Filters: ZWO 31 mm RG, ZWO 7nm Hα

Mount: EQ-6 (EQMOD)+PEC

Guiding: Finder/Guider+DSI IIc+PHD 2.6.2.4 (Win 10 ASCOM)

Camera: ASI1600MM-Cool, -20 °C, acquired Hα 1x1 RG 2x2, Gain 300 Offset 50 

Acquisition: Sequence Generator Pro 2.6.0.3

Exposure: 80x180 s Hα, 55x45 s R, G

Stacking: Neb 4.1.2, flats & darks, trans+rot align, Nebulosity 1.5σ stack. Processing: too extensive to detail

Review of ASI1600MM-Cool Camera Kit with EFW8 31 mm LRGB, Ha, SII, and OIII filters

My best DSI IIc HαRGB image of IC 405

First light ASI1600MM-cool+EFW+AT8IN image

I have used a Meade DSI IIc for a number of years and have long wanted a cooled monochrome camera with a larger imaging chip. I initially didn’t even consider the ASI1600MM-Cool because it uses a 12-bit CMOS chip which I thought inferior to the 16-bit CCDs. However, several things changed my mind. First and most importantly, I saw a lot of outstanding images on Astrobin that were produced with the ASI1600MM-Cool. The proof of the pudding is in the eating, and it is hard to argue with really nice results. Second, as I researched a bit more, I realized that the read noise of this camera is very low, compensating a great deal for the lower bit range. Third, the price for this camera is much lower than for a cooled CCD of comparable size. In addition, while ZWO’s prices are low, the kit looked like a good deal compared to buying the components separately. Finally, High Point Scientific had the kit for $100 less than I could find it anywhere else, so I finally convinced my wife and made the purchase. I ended up with a complete LRGB and narrowband imaging system for less than the price of a CCD camera alone. So even though this kit cost as much as all the rest of my gear put together, I still consider this "cheap," or at least economical, astrophotography.

I received the kit and installed the filters. I chose the 31 mm filters hoping to avoid any vignetting with my 800 mm F/4 AT8IN Imaging Newtonian with an Orion Thin Off-axis Guider (TOAG). The 31 mm unmounted filters are dropped into the filter wheel and held in place via 3 small screws with rubber washers. It took some careful work to install them. I was happy to find that the same wheel is threaded for 1.25” mounted filters, so I put a mounted 1.25” Baader UHC-S filter in the 8th slot. The kit comes with a nice set of adapters and I had no trouble screwing the camera directly onto the filter wheel with the TOAG on top of the filter wheel and some T-spacers to get the right distance from my coma corrector.

Best previous image of IC 410

The biggest snag in setting this system up came with getting the camera and filter wheel to talk with my software. I have a somewhat unusual setup: I use Sequence Generator Pro under Windows 10 on a MacBook Pro running the most recent version of VMWare under MacOS Sierra. After some fumbling, some support from the ZWO users forum, and some trial and error I discovered that VMWare has to be set to USB 2.0 to enable image downloads with my configuration. The system is also sensitive to how things are cabled. Using the USB 3.0 cable that came with the camera coupled with a 20-meter USB 2.0 repeater cable (so I can run the system from my warm living room!) did the trick. I connected the filter wheel through the USB 2.0 hub on the camera and that works fine, but I opted to connect my guide camera (a Meade DSI), mount, and focuser through a separate USB 2.0 powered hub and repeater cable. Since I got things cabled up correctly, everything has worked flawlessly.

ASI1600MM-Cool HαRGB IC 410

The performance of the camera/filter wheel combination has been everything I’d hoped for and more, except I do get some vignetting in the corners with my optical setup, especially with the narrowband filters. I love the much larger field of view and much higher resolution and sensitivity I get with this camera relative to the DSI IIc. The learning curve in switching to monochrome imaging has been steep but fun to climb. So far I have imaged 4 targets, and each image is far superior to the best I could get previously. I’ve used the H-alpha filter in each of these. The L, R, G, B, and H-alpha filters appear to be parfocal; in any event, I have have gotten away without refocusing when changing filters. I haven’t tried the SII or OIII filters yet. My images are posted at www.astrobin.com/users/dvdearden.  

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Some comparisons are shown here, although the size of the images posted here probably doesn't do them justice.

In conclusion, I’m very happy with this camera+filter wheel+filter set combination. I can finally get images with sufficient resolution and quality that I’d consider printing and displaying them. I expect to enjoy this setup for a long time.

Best previous HαRGB Jellyfish

ASI1600MM-Cool HαRGB Jellyfish