vlaiv

It's very hard to guess what could possibly cause elliptical shape of halo. Maybe we should try analytical approach? Size of diffraction spike depends on length of straight edge that causes it. Circular aperture can be seen as bunch of very short straight edges each at slightly different angle - that creates great many weak diffraction spikes each perpendicular to its own forming edge - these join together to form uniform halo. In order for halo to be elliptical - diffraction edge in one direction must be longer than in other direction and yet uniformly curving to form almost complete / smooth halo (halo in the image is not completely smooth - it has some spikes - due to segment of cable being straight). I think that it must be section of ellipse as well. One simulation later .... (left - aperture, right PSF blurred with gaussian blur and stretched to show halo). This only shows that one must cable-manage!

Maybe this helps? Or maybe if I rotate it 90° at a time instead of flipping it: I still think it's there.

It's hard to tell on reduced image, but I'm having a sense that star halos are elongated in diagonal direction (bottom left - top right)? Is it just me, or is this real?

I don think it is much worse than doing it with B mask, is it? I mean principle is the same - except you look at the numbers instead of spike pattern. As for B mask precision, well, I'm not an expert, or to put it more precisely - I have almost 0 knowledge and experience with it Used it couple of times, saw that I don't get good focus and decided not to use it anymore. Have two of them gathering dust (one for each imaging scope).

I don't use APT, but here is APT help file section that describes focus aid tool: https://astrophotography.app/usersguide/focusing_aid.htm# It shows both FWHM and HFR values. You should not look for particular values in either - they are both relative, and smallest value indicates best focus, but it will change from session to session as it depends on both seeing and guiding performance. Idea behind using those is to use short frame & focus exposures (but make them at least 2-3 seconds long in order for seeing to average enough) and monitor values. Tweak focus until you get the lowest number. Numbers will change each time you make focus adjustment and you need to change focus until you get lowest values (that will include going "thru" actual focus position once or twice as you need to verify that numbers first fall and then start to rise once you go thru the actual focus position - pretty much like focusing visually - you rack focuser in/out until you are certain you have the sharpest view).

If you want to search for progressing defocus - just visually compare first and last sub of the evening. First sub should have tight stars and last one should have stars as in above image. Difference should be obvious.

I like tight stars as well in the image and think that processing nebulosity separately via Starnet++ is good approach for NB. What confused me is presence of some of the stars while others can't be seen at all. For comparison, here is similarly deep image (taken with UHC filter, so almost narrowband in nature) - showing plethora of surrounding stars:

Yes. Check individual subs to see if there is progression in defocus. As telescope cools down - tube gets shorter because things shrink at lower temperature. If there was rapid temperature change during imaging session and you did not refocus (people usually just focus on the beginning of the session) - it can lead to loss of focus over time. Another possibility is that scope was not properly cooled when you focused - if you focused at the beginning quickly after putting the scope on the mount and that it cooled before you started imaging. Third option is simply - poor judgement of bahtinov mask pattern. I don't use B mask at all as I've found that I can't reliably tell if I have good focus with it or not. It is far easier to just check stars on computer screen and look at FWHM / HFR values.

Yes, it does look like little bit out of the focus. You can see that on fainter stars - they are also like little discs rather than stars. Bright stars can appear disc like due to stretch - but faint ones should be pin point like - and they are not - they look like small circles.

I like the image, but where are all the stars?

Quite strange - I mean vignetting affects light that comes in thru the aperture of telescope - regardless if it comes from the stars or flat panel. You should see it both in your flats (as you do) - but also in your uncalibrated lights.

That is interesting. Did you change focus position between flats and lights maybe? Change in focus position can lead to vignetting - but it usually requires racking focuser further out. What do you use for flat source?

High DEC lowers your calibration precision significantly. You can also choose side of pier when calibrating near DEC 0° as well. Not sure what you mean by mount imperfections on either side of pier and how it relates to good calibration of guide system?

What do your flats look like?

https://www.teleskop-express.de/shop/product_info.php/info/p6041_TS-Optics-2-m-RJ10-extension-for-Skywatcher--Orion-and-TS-Optics-Steeltrack-Motorfocus.html It appears to be RJ10 You can also go with wireless connection: https://www.firstlightoptics.com/skywatcher-focusers/4tronix-focusrf-remote-control-for-dc-focus-motors.html

Not sure if you got it right there. Do you think that RASA8 will magically collect more photons than any other 8" scope? Number of photons falling on 8" of aperture does not change when you change the scope. 8" F/8 RC will be equally fast as RASA8 if you utilize the same "effective" pixel size in both (pixel size in units of arc seconds in the sky and not micrometers). Only difference will be in FOV between the two. That is the strength of RASA8 - covering more sky in the same amount of time than would be possible with longer FL scope. Tradeoff is sharpness / detail. Longer FL scope would be able to resolve more if it has smaller spot diagram (and in most cases that is true). You can't do planetary imaging with RASA8 for example. Two major things to consider when choosing exposure length are: - impact of read noise. You need long enough exposure so that one of the noise sources that changes with time (shot noise, LP noise or thermal noise - each grow with exposure time) swamps fixed amount of read noise. - full well capacity. You can and will saturate pixels in single exposure. That happens with bright stars and sometimes even with bright parts of targets. Luckily, there is simple way to deal with that - just take small set of short exposures at the end of session and use those values scaled to fill in saturated parts of original exposure. There are other considerations that are not as important - like thrown away data due to tracking issues or maybe wind (sudden wind gust can ruin either 30s or 15minutes - depending on your sub duration). Some algorithms work better when they have larger number of subs to work with (sigma rejection and similar).

Different FF/FRs have different amount of vignetting and if you changed that component of optical train - then yes, level of vignetting will change.

Therein lies the issue - DEC normally is not tracking and will stay still for most of the session - only slightly deviating from its starting position (very slow drift due to PA misalignment). In ideal case - DEC does not even need tracking and can stay still for the whole session (very stable mount - no wind issues or similar and excellent polar alignment). 120s of sidereal rate means that DEC needs to move at least 120 * 15 = 1800 arc seconds = 30 arc minutes = 0.5°. That simply does not happen with even very poor polar alignment - if you are 1° away from Polaris (two moon diameters) - drift rate will be 15"/minute, so you would need about two hours to get 0.5° of drift and move DEC axis for "120s" total. Only way you can detect is if you are lucky enough to start with DEC close to problem point and that there is enough drift to move it past that problem point.

Fancy a bit of DIY? https://sourceforge.net/projects/arduinoascomfocuserpro2diy/ That is complete motor focuser that can be connected to computer so it can be fully automated. I'm sure hand controller can be added if you wish, but if it is for imaging - I think it is better to have it automated.

Not sure there is sensible way to test that though.

In that case - I would examine pulley on RA motor shaft. It has same number of cogs as original gear - which means that period of single cog is 13.6s (13.6s * 9 cogs = 122.4s). If your disturbance lasts for 25s - that would be roughly twice that period of 13.6s - which points to single or pair of cogs doing something funny. Take magnifying glass and look at it close up to see if you can identify the problem. I've found that looking at the mount while tracking sometimes helps to identify the problem. I sorted tension related issue that way (it was happening each 13.6 because of improper belt / pulley meshing).

Don't touch gamma - leave it at default setting. You want your data to be linear for stacking.

Come to think about it - yes, since these stepper gears are on shaft of the motor itself - swapping motors will swap gears as well, and since motors are the same - it is simple way to do it without needing pinion extraction tool.

They probably are the same and my guess is that you won't see any difference. ~120s period is one single revolution of stepper gear. If you have significant wobble in that period - try swapping stepper gear instead of stepper to see what happens. Mind you - these are very difficult to remove - you need pinion extraction tool for Heq5 for that (it comes with Belt mod, but could possibly be purchased separately).

First - use histogram only as a guide if you are close to saturation - which you won't be in this case. Set exposure time to ~5ms. Use gain to select low read noise rather than to "get good histogram" - which is meaningless in planetary imaging. If you have Color camera and you used IR cut filter - you should get color images. What software are you using for stacking? If you are using AS!3 - set bayer matrix to RGGB and let it produce color image - if you are not using AS!3 - well, switch to AS!3 I like images btw. Jupiter one seems very good - a bit more care in processing and it will be very nice image.