Staring @ the Sun, 83

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Tweaking the solar kit

07/21/2021. In case you need to know this
, inserting a 20mm extension between the ASI120 and the tilt-plate with the integral barlow produces a solar disc 3490 pixels across. That's a plate scale of 0.54 arc seconds per pixel. Doesn't sound like much of a difference (0.54 vs 0.66), and I can't tell what the effect on the image quality is because with the extension in place, Newton's rings are back. Go figure. I settled on the lesser focal length with the camera close-coupled after just a few samples.

Listen, if you want something that sounds impressive, consider the popular notion of the 35mm "equivalent focal length" of crop-sensor cameras. Under that rubric, the ASI120MM and this telescope are working somewhere about 7,800mm "equivalent focal length." The actual, real, genuine focal length at the image plane is around 1,172mm (see previous page).

I enjoyed good polar alignment and good seeing at the lake access lot this morning, but a slight breeze was sometimes troublesome (so I selected a little more gain, 40, and a considerably faster shutter speed, 2ms, than last time). Increasing display brightness and selecting an exaggerated display contrast made focusing much easier. I kept the histogram display in view and kept highlights at or below level 220 (of 256). I saw no speed difference with or without the live histogram display, contra some advice online, but my frame rates are so low that's not much of a surprise.

I tried some 16-bit .SER files for comparison with my usual 8-bit .AVI files. At first glance, I'm better off with a 1,000 frame 8-bit AVI than with a 250 frame 16-bit SER but that's just one session's impression. The frame rate is cut in half (down to 7 fps) with the extra data in the SER files. When we get some really bright flaring, it will be worth trying again. Today I am less impressed with the 1.5x drizzle option in AS!3. I got my best results today without drizzling.



Not that there's anything wrong with .SER files.
Best 25 of 250 frames, 16-bit.



Coming attraction.
Best 250 of 1,000 frames. 8-bit.



A whirlpool on the Sun.
Best 125 of 250 frames. 8-bit.


iron filings

Iron filings anyone?
Best 250 frames of 1,000.


2021/07/23. I out-waited some small but glacial clouds, discovered a light-leak near the camera that's costing me contrast especially on prominence photos, customized the clip limits in ASIStudio (now I can do 500 frames and it no longer offers a few options I would never use). I've experimented (again) with the balance between gain and exposure, and am still just generally learning to get all my software doing what it should be doing. I just look at the clips and decide which are best focused, steadiest, etc., then run "Analyze" in AS!3 and take what it shows me into consideration: I don't take any images in the lower 50% of sharpness, and usually only the top 15-25% depending on how many frames are available -- taking less than 75-100 is seldom a good idea. Here's today's take, near noon from the lake access lot:









This one is the best 250 of 1,000 frames.


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, an ASIair (model 1) and sometimes one of several laptops. A good many images come from an unmodded Canon 6D but a lot more will be coming from an R6. Video and video extracts begin in a Canon EOS M, usually running in crop mode via Magic Lantern firmware (but the 6D and especially the R6 will probably see more use). Telescopes include an AT10RC, 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 on the Canons. A solar Frankenscope made using a 90mm 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 (Autostakkart!3 is my current fav for image stacking). Mounts include an iOpton SkyTracker (original model), a bargain LXD-55, a Losmandy G11 (492 Digital Drive), and an Astro-Physics Mach1. PixInsight does most of the heavy lifting; Photoshop polishes. Some of the toys are more or less permanently based in New Mexico. I desperately hope to get back soon.


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                   © 2021, David Cortner