The Starry Night, 196

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2020/12/05. And you may ask yourself, how do I work this? and why isn't that picture in color? Or why isn't it sharper? Or why isn't it deeper than it is? It's like this...



M31. iOptron SkyTracker.
79x60s L; Gain 200; -15C. ASI1600MM and 135mm Nikkor, stopped to F2.4.
A tight crop. Dark-frame calibrated, no bias, no flats.
Messed with using Starnet routines in PixInsight.


I set up a sequence (L, R, B, Ha) using the "autorun" feature of the ASIair, but it would only execute a few (or several) frames, then terminate. After that, pressing the "do it" button did nothing useful. The 5 second delay would count down, and then -- nothing. The status would change to "shooting," but nothing suggested that anything was happening, and things just sat there waiting for the heat death of the universe. So I restarted everything with the same unsatisfactory results. It finally occured to me that something failed when the sequence cycled to anything but the "Luminance" filter, so I shot nothing but luminance until the Moon came up and then brought the kit inside to diagnose the issue.

I tried new cables from the camera to the EFW (Electronic Filter Wheel) but saw no improvement. I tried a different USB port on the camera (nope) and tried plugging the EFW into the ASIair rather than into the camera's USB 2.0 hub. Nothing.

Naturally, attention next settled on the EFW itself. When I told the EFW to change filters (directly, not in an autorun script), I got the error message: "fail to operate." The message had previously been hidden by an on-screen image review. I started taking things apart hoping to find a mechanical issue, and I did.

Here's my theory: the Baader filter cells are about as thick as the EFW-mini can accommodate. After being bounced around for a couple of years, the filter in my #3 slot ("B") had backed off in its socket by between 1/2 and 1 full turn. That added 0.5 to 1.0 mm of thickness where there is very little room for it. That excess thickness was enough to drag against the inside of the filter wheel's enclosure. I tightened the filters down; put it all back together, and it's all working again.

But all is not entirely well: the iPad Mini 4 shut down five or six (too many) times during tonight's session. I plugged it into a USB outlet on the power pack. It shut down. I plugged it into the wall. It shut down. Every several minutes, it just cycled itself. I solved that problem in classic American fashion: I threw money at it. Amazon will hand me a Galaxy Tab A 8-inch tablet later this week. I expect it to become my primary display for the ASIair. When I finally get out west again, I'm not going to bet the trip on a tablet with undiagnosed power issues. Maybe the G-Tab A will run DJI apps, too -- the jury is out on that one. If so, I can repair the iPad at leisure. As a bonus, shifting my ASIair control to Android allows me to back out the latest releases in case of trouble, something that (last time I checked) cannot be done under IOS.

So now let's talk about focus, which seems piss poor in the tight crop shown above despite the focus routine reporting FWHM as just 1.5 pixels. The inner structure of the star images is nothing to brag about, either, so I can't really tell if the step-down ring helped much. Field illumination is better but still not great. Anyway, until I actually find the best focus, there's no point in suffering much about the rest.

Next time, I've moved my strongest ball head (Sirui 40) under the mount and the new, smaller one (Sirui 20) under the camera atop the tracker. I might lose a few degrees of sky way down south with this saner arrangement, but then, I may not [eta: I don't]. I seldom have a clear view of the southern horizon anyway.


New arrangement of ball heads. Drop back a couple of pages for the "before" photo.


ASIair single-point failure opportunities concern me. I'm fanatical about multiple backup microSD cards, for example. I use the physically small USB drive seen in the photo above to collect images so I don't have to pull the critical SD card after every session and reinsert it. The microUSB power port on the RPi board has always felt somewhat fragile. I've ordered a right-angle male/female extension for it. That should make attaching and detaching the power cord less stressful on the ASIair's components and isolate wear and tear in an easily replaced part. It might help a smidgeon with cable management at the same time. More when I know more.


What Kind of Tablet do I Need to Run the ASIair?

This question comes around now and again on the forums. I love my iPad Mini 4 for ASIair (and for DJI's flight app), but it's developed a nasty habit of reporting zero battery power when there is, I am sure, plenty. Bang, zoom, black screen followed by the plug-me-in icon. Restart, plug it in if possible, and all will be OK. For a while. Sometimes that behavior is just irritating, but it's particularly irritating while setting up an imaging run under a rare clear, dark sky, and it's especially irritating when controlling a drone half a mile away above some watery wilderness. It might be a battery thing. It might be a power connection thing. But I am not paying Apple $300 to figure it out. For far less, I could buy a new Samsung Galaxy Tab A tablet and be done with that particular issue (reports are mixed about how well the Tab A runs DJI's app, but first things first). Done. I'll probably eventually put a new battery in the iPad myself or have one put in and hope for the best. We'll see.

D'oh! Then it occured to me that the tablet is just a display for what the Raspberry Pi, aka the ASIair, is actually doing, so even my old iPad 2 might suffice. Worth a try. At the moment I have three tablets all running the s/w v1.5.2 on my ASIair whose firmware I just updated to v6.92. Stay tuned for more about deepsky imaging using:

1) a Samsung Galaxy Tab A 8-inch 2019 edition; Android v10

2) an Apple iPad Mini 4; ios v14.1

3) an Apple iPad 2 (circa 1915, or so it seems); ios v9.3.5

All are pretty minimal configurations. According to some reports on the Facebook ASIair users' page, older tablets running version 9 ios may launch the app but encounter trouble in actual operation. Clear weather, please, and then we'll see what's what.



My deep-sky photos are made with a variety of sensors and optics. Deepest images come now from a ZWO ASI1600MM Cooled Pro CMOS camera. A good many images come from an unmodded Canon 6D. Video and video extracts begin in a Canon EOS M, usually running in crop mode via Magic Lantern firmware. Telescopes include an AT10RC (a remarkable budget Ritchey-Chretien astrograph), an Orion 10" F4 Newtonian, and a pair of apochromats: a TMB92SS and a AT65EDQ. A very early Astro-Physics 5" F6 gets some use, too. So do lots of camera lenses on both the ASI1600 and the Canon 6D. A solar Frankenscope made using a 4" F10 Orion achromat and the etalon, relay optics, and focuser from a Lunt 60 feeding a small ZWO camera will see more action as the Sun comes back to life. Mounts include an iOpton SkyTracker (original model), a Losmandy G11 (non-Gemino), and an Astro-Physics Mach1 CP3. Software is PixInsight for heavy lifting and Photoshop for polish.


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                   © 2020, David Cortner