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Depending on the speed of your scope and tube type you might need to refocus on every 1-2C of temperature change as well. There is a way to approximately calculate this, but it's a bit involved - you need to figure out material of the tube, length of the tube, critical focus zone depending on the scope speed and such and then see how much temperature change will not move you out of critical focus zone. If you don't want to do calculation, I would say for regular steel / aluminum tubes rough values would be - scope less than F/5 - refocus every ~1C of change, scope F/5 or slower - 2C.

Did you look at Lum subs? I've just looked lum stack and not color (yet). It could be that only few of subs are out of focus - it can happen due to temperature shift during the imaging session - tube gets shorter and there is focus drift. On the other hand, it could be due to Lum filter not being parfocal with other filters if you did not refocus on each filter change.

Indeed. Flat darks are just darks for flats - same way you take darks for regular lights - you do the same for flats. Same exposure duration, same settings, everything the same as flats except you put scope cover on to block any light.

I've got a couple of pointers, hope you don't mind me having a go a this data. First - focus is unfortunately a bit off in luminance (have not yet checked other filters). It's a pity as image could have been sharper. If we don't display image at full resolution - we can hide this defocus so it won't be terrible. Here is what I mean: See stars being little circles instead of pin point objects? This is due to slight defocus. Second - you did not take flat darks and your calibration is not ok. This can be dealt in several ways - one is doing synthetic flat and I'm going to do that for this quick processing. Other is to take flat darks - which are darks with exact same settings as flats and use those to calibrate your subs with. If you don't use flat darks - your flats will under correct and it shows in your sub - there is still some vignetting left as this 10x10 bin and stretch shows: Now for processing - I'll bin data because your stars are not pin points and there is not much point in going for full resolution. This will boost SNR as well so image won't be as noisy. Here is what I was able to pull out of luminance: Will try to add color tomorrow

Just some info - I've used very short flats - a few milliseconds long exposures with my ASI1600 and did not have issues with flats. Just made sure I was using matching darks (also few ms long - exactly the same settings as flats).

I really enjoy posts like this one. Very interesting and informative. Just to clarify, kit used is BK MN190 DS + ZWO ASI174MM-Cool?

@William Productions Have a look at this thread, might be of interest to you if you opt for either SA or SAM:

Maybe dropbox or some other file sharing service like we transfer? We transfer does not require login / account, won't keep files for too long, but long enough for interested parties to download. I think it's couple of days now that files are being kept for download.

Telescopes come with 3 different attachments (most of the time) - regular sized scopes have what is called Vixen level dovetail / connection. Larger scopes sometimes have Losmandy dovetail and very small scopes are sometimes attached via 1/4" thread (same as photo accessories). Often with small scopes Vixen dovetail has also 1/4" thread. Above is SW 72ED and it has small vixen level dovetail attached to rings. It also has two 1/4" threads for attachment to photo tripods. iOptron SkyTracker has 3/8" and 1/4" connections, and you would need something like this to pair the two: https://www.firstlightoptics.com/adm/adm-mds-dovetail-plate-adapter.html This is vixen level dovetail clamp that can be screwed onto 1/4" thread of SkyTracker mount. Btw SkyTracker has 3kg payload capacity while SW Star Advanturer has 5kg load capacity, thus SA would be better suited for a small scope, while skytracker can carry ball head, camera and lens.

I really don't know. I have not used any of them and since they are portable small mounts - was not very interested. I do have AzGTI that I plan to put in EQ mode and use it like that. It is another option, and I think it is better - because it allows for guiding in both RA and DEC direction. Star Adventurer only has guiding in RA. That is probably something that you should not worry about right now - it will be just too much information and additional expense to get auto guiding running as well. It would be best for someone who used either to offer their advice here, or maybe to have a look online to find some reviews of both Star adventurer mini and regular, for example these: http://philhart.com/content/star-adventurer-review http://philhart.com/content/star-adventurer-mini-review There are couple of other mounts in this class as well that's worth having a look at, for example: Az GTI mount: https://starlighthunter.com/articles/az-gti-equatorial-mode/ (there is also thread here on SGL, or even couple of threads discussing az-gti, worth having a search) Then there is iOptron offering: https://www.firstlightoptics.com/ioptron-mounts/ioptron-skytracker-pro-camera-mount-with-polar-scope.html Vixen offering: https://www.firstlightoptics.com/vixen-polarie/vixen-polarie.html There is of course other possible path for you to take - get most important thing first - get good mount. Something like Heq5 class mount (second hand - this would be my choice) or EQ5 new. Use mount and camera and kit lens to familiarize yourself with astro photography and then, when you save some more money - get telescope to image with.

Hi and welcome. With that sort of money there is really only one option and that is going to be rather tight. Look at 72mm ED doublet from skywatcher and star adventurer mount. Such combination is good for what you are after - larger things like Orion nebula and Andromeda galaxy. Anything bigger than such small portable wide field setup is going to cost much more. Next mount in size is about the whole budget unless you shop second hand. 80ED scope is also about that much new (with accessories that you are going to need). In fact even Star Advernturer and 72ED doublet is likely to get you over budget once you add needed bits and pieces - like LP filter and T2 adapter for your camera and such.

Ah, sorry, I should have been more specific. I wanted to suggest you to upload original .fits straight from camera so I can check actual pixel values and do some statistics with the data. Scaled down jpegs are of no use for that purpose.

Could you post following: 1. light sub 2. dark sub (or master dark) 3. flat sub 4. flat dark sub (or bias if that is what you are using instead of flat dark)

+1 This is rather good way to do it if they contain sensitive information as you won't be leaving a copy on third party server

Do check spacing as well - just to make sure.

Although large imaging circle refers to optics correction rather than vignetting - in most cases larger imaging circle means larger unvignetted portion. You should not concern your self with corner vignetting - it is not related only to telescope, sometimes other parts of system can introduce a bit of vignetting - like correctors and filters unless they are very large, but in any case - flat fielding solves that.

There is a maximum compression that can be achieved on a set of data - it is amount of information data actually holds - you can't write it smaller than that if you want to maintain whole information. If data is already "tightly packed", or does not contain any redundancy in information storage - you can't do anything to compress it beyond what it will allow. It looks like PDF is already very close to what is information content and can't be compressed further much.

I'm seeing multiple aberrations in star shapes. This is typical coma: Parabolic newtonian telescopes and SCTs have coma aberration. As far as I know - x0.63 reducer should be both reducer and corrector and should remove coma. This other corner shows coma + astigmatism: With setup as yours this usually means that you have a tilt in your system. If one corner is affected and others are not or there is different aberration present - it means that sensor is tilted with respect to optical axis and corners are at different distance to corrector because of that. Check corrector spacing and connection to camera. Reducers/correctors have a working distance - make sure you get it right to remove coma. For astigmatism - make sure your camera connection is straight and firm (does not sag under camera weight).

There is something strange about two of them as far as I could see. It took quite an effort to fix it in processing. I even came up with completely new method of doing it while I was attempting to process the images. I'll do quick stretch on one of the images to show you what I mean. In fact, here is the other one: Gradient is not regular gradient - for some reason there is "hole" in the gradient and it is centered on object (or frame and object is in center of the frame so they align). This feature is very hard to process and to get nice smooth, uniform background. Btw - you provided 16bit stacks - it's better to work with 32bit data.

What software did you use to stack this with? Maybe you did not load calibration files? This image shows both issues with flats - dust shadows and issues with darks - there is amp glow visible in top right corner. This could happen if you forgot to add calibration files or like I said, dark optimization was turned on for stacking and messed up dark calibration (hence both flat problems and visible amp glow).

You need to "guess" it - by looking at histogram. It needs to be to the right but it must not clip in any of the colors (there will be three peaks and all should be visible and not clipped to the right). Once you find exposure length that works - shoot flats with that exposure length and remember it. Then shoot flat darks with same exposure length.

The one you used to calibrate / stack resulting image that shows dust shadows. I'm guessing that you used same data as first stack. First stack does not show any issues with flat calibration - which means flats are fine. Dark optimization works by scaling darks - something that you can do only if you use bias files and bias are stable enough (this seems not to be the case with CMOS sensors / cameras as far as I can tell). For this reason it is best to turn this option off as it can cause issues with flat calibration.

I've seen on numerous occasions that people have issues with APT and automatic flats. Could be that it is issue with flats. How about doing flats "manually"? Avoid any automatic procedure for flat creation and just shoot regular "light" subs with flat panel and stack those yourself to see if it will help?