vlaiv

Background looks kind of blue and yes, stars are nowhere to be seen - except in galaxy of course I personally find the image strange because of what I'm used to seeing in M31 images - there are certain stars / groupings of the stars that I expect to see - and some of them I use to judge quality of the image. For example - great images of M31 start to resolve individual members of NGC206 Your initial image: Last rendition: Reference image found online: Then there is "4 in a row" how I like to call that asterism: Good M31 image will have those resolved and tight. Here are they in luminance of M31 that I took some time ago: But they are completely lacking in your last rendition.

I think it is kind of funny calling "starless" image of something consisting out of stars

I'm not very good at discerning focus with Bahtinov mask - that is why I never use one. I prefer FWHM and looking at the stars on screen (not sure how would that work with DSLR - if you can see stars on computer screen or you don't use computer at all). Btw, data is good. SNR is good. I did quick processing and I did not need to use denoising at all. In fact, I was able to do some nice selective sharpening and still keep background smooth. Only issue is with dark calibration (to be expected when camera is not cooled) - there is some unevenness in the background. Here is the result of processing: (for some reason I prefer this orientation on M31 - it took me a while to figure out which way it goes ).

How can you tell if you have good focus there? If I look at this part of image - that looks like serious asymmetry to me: (look at three little balls of light right next to star - two on left are closer together than one on right).

Have you tried double exposure dark trick? I spent some time thinking about it and even if bias is not stable you can try to optimize darks by following approach: Take dark of 60s and take dark of 30s. When you subtract them you should be left 30s pure dark signal (this of course works if bias is stable in long exposures and only causes issue when taken on its own. We know it is stable on same exposure length as that makes dark subtraction possible). You can then use 30s dark and remove pure 30s dark signal to get bias (which you would not be able to record otherwise - like using regular bias with 0 exposure).

Yes, but there are mounts capable of 0.3" RMS or even less - that are not in price bracket of those you listed. Mesu 200 and GTD E-Fric come to mind as more affordable yet premium performance wise mounts. I'm not sure I can provide you with reference to a text that discusses that in context of astrophotography per se, but do have a look at following articles (basic info that you can sort of piece together): https://en.wikipedia.org/wiki/Airy_disk (pay attention to Gaussian approximation) https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem https://en.wikipedia.org/wiki/Spatial_cutoff_frequency https://en.wikipedia.org/wiki/Fourier_transform (note 2d gaussian shape and its transform) https://en.wikipedia.org/wiki/Convolution_theorem That is about all that is needed to determine optimum sampling rate, and here are few more pointers that help put above together: - Seeing blur is given as Gaussian kernel of certain FWHM. - Guiding error produces blur that is again given as Gaussian of certain sigma - Telescope aperture produces airy disk pattern that can be approximated by Gaussian - These three blurs convolve to produce final blur and their corresponding variances add up (standard deviations add in quadrature as square root of sum of squares). - Fourier transform of Gaussian is Gaussian and Gaussian falls of to 0 at infinity. At some point you can take it to be cut off frequency (for rule of x1.6 above I used when frequency domain Gaussian falls below 10% as cut off frequency). - For planetary imaging - you can use actual spatial cutoff frequency as Fourier transform of airy pattern is MTF and that hits 0 at cut off frequency (unlike Gaussian that only tends towards zero).

What software are you using for flats? What is your offset set to. Did you calibrate your flat in any way? What does the raw flat sub look like. In fact - can you upload one for inspection? Sometimes there is some sort of clipping that will produce weird artifacts on flats. If you are using software flat assistant - try shooting flats manually / manually setting exposure time and manually calibrating it to see if there is difference.

How bad can it actually be? Flat exposures are very short, even if there is significant amount of dark current - signal will simply be stronger. ASI294 has less than 0.5e/px/s for 25° sensor temperature. Even if we double that one or two times - we are still much lower than shot noise per sub if sub is taken at say 60-75% FWC which is 63.7K. Even with higher gain, if FWC is reduced to say 4K, shot noise is still like 20-30 larger than dark current noise so contribution of dark current noise is negligible for flats here.

Possible dust buildup on the lens. Lens is always exposed to dust - cover or not. Question is how big is the level of exposure. If you leave it like that for a few days - you probably won't notice it, but there will be a bit more of it then otherwise. That however does not impact quality of the views / images, and can be removed with bulb blower, special cloths and lens cleaning liquids from time to time (just be careful - hard bits of dust when wiped away aggressively can scratch the lens and/or coatings on them - that is not something you want).

Here is quick editing example of what I meant: I took that orange kind of glow - but you will probably want to balance it with other light sources in the image. Maybe I selected too orange / brown color for this. this is how I handled it in Gimp - I added copy of layer - erased that top part and added uniform orange / brown to it and then added gradient mask to that part. I controlled overall opacity of top layer to control the effect.

I guess you have those two as two layers? Take Orion layer and put layer on top of it - select grey color. Add layer mask to that layer and create gradient in layer mask so that you get gradient opacity on it. Adjust that layer transparency so that it does not start fully opaque. That should do it.

Maybe add a bit of murk to the background Orion image close to mountain tops - to get a bit more realistic feel to it?

I vote iOptron. Do consider using better tripod like Berlebach instead of stock steel tripod for better stability, but check from portability point of view if it will suit you. I added Berlebach Planet to my HEQ5 and it made a huge difference. Btw - you don't need guiding for planetary imaging.

Here is an example of how much noise there is in amp glow areas. This is single dark from my ASI1600: You can see two areas on the right side and some of it on top left. I'm now going to subtract two dark subs (that will eliminate offset, dark current and amp glow signal) and measure noise in center of the sub and to the right - say bottom part where there is amp glow. StdDev column shows noise. This is 240s dark exposure, and above noise is read noise + dark current noise of a single sub (I divided with square root of two because I subtracted two subs). In one case, noise is slightly above read noise of 1.7e being about 1.93, while in corner it went up to 2.85e Both of these are smaller then read noise only from very good CCD (which would be around 4-5e). This is signal in dark part and brightest part of amp glow: Offset is not removed here (was set to 64), but you can see that increase is about 3.5e per 4 minute exposure in amp glow area.

It is one of those "scary" words young imagers are being frightened with If handled properly - amp glow is non issue. Even amount of signal is very small so associated noise is not very big either (comparable to read noise in normal exposures). I guess problem is because people are thought the wrong way of doing things when using DSLR. Often they are told - don't do darks, do just bias and you'll be fine. It turns out that doing just bias is not proper way to calibrate and if you have amp glow - it won't go away.

That is fairly close already. Not sure if you could even fit helical focuser in there.

Maybe simplest solution is to get one of these: https://www.teleskop-express.de/shop/product_info.php/info/p4591_TS-Optics-short-T2-Helical-Focuser---Adapter---camera-does-not-twist.html On the other hand - how fast is your setup? Small changes in focus position will have large defocus only on fast system. On slow system defocus will be much smaller. I'm asking this because OAG position should be as close to sensor on fast system to avoid vignetting of prism.

I see your point, and yes - no point in throwing an achromat in there as it has "dead giveaway" feature, but what about 4" mak?

Not sure if that is needed. We can simply do the test between two same class scopes - to see which one performs better and by what margin. For example - I did small shootout between 4" Mak and 4" F/10 achromat on Jupiter this summer. I was actually surprised that frac pulled ahead and by how much. I think main issue there was thermal stability and will love to do the test again. Frac had obvious color issues - but view was sharp end detail was there (more than I expected). If I had color rendition of Mak and sharpness of that achromat in say 4" F/7 ED - I'd say that is as good as 4" aperture can provide and would be surprised if any 4" scope could deliver significantly better image, cheap or expensive.

I love the image. I'm just slightly sad that it was not captured in one go - that would have been jaw dropping, however, I do appreciate level of preparation and effort that goes into getting the bits needed to do the composition.

And what about all the scopes in between?

Those Hyperion eyepieces are interesting example. I've read so many reports on those and wonder how come they are still being made. So many reports said that they are not worth asking price. Never tried one of them myself though so can't really tell. Are they really that bad?

You already have color AVI. Debayering already color image will give you B&W image. Just tell it that it is already color (like on auto) and you'll be fine. If you want AS!3 to do debayering - then choose SER format and shoot in RAW and not color.

I just had a discussion on my local forum and learned something interesting that I would like to discuss. We often hear of some scopes working at stopped down aperture in comparison to what has been declared and there are tests to measure actual aperture involving lasers / torches, etc ... I've learned about rather interesting way to test if aperture is stopped or not in telescope. It is not convenient test to measure how much stopped down aperture is - it is just a test if it is or not (one can then proceed to repeat the test with ever smaller apertures until one matching true aperture is found). Test consists of creating square cardboard cutout / sort of square aperture mask with diagonal being aperture that is being tested. Say I want to test if my Maksutov 102 has 102mm of aperture and it is not stopped down by baffle or something. I would make square aperture mask with diagonal of 102mm I would then take eyepiece - focused to infinity in the scope and put aperture mask in front of the scope. I would then observe exit pupil at large distance (or record it by camera). If I see perfect square with sharp corners - aperture is not stopped down, but if I see corners being clipped - then aperture is stopped down. I had a go with finder and its cap (not square - but I just wanted to test the effect) - and indeed, from far enough, FOV gets tiny - but shape of field stop becomes the shape of aperture - if I place cap half way on the aperture - I see semi circle blocking the exit pupil. If I look from close thru the eyepiece - I see nothing at all (which is to be expected).

What about independent testing? We simply record sight thru two different scopes and compare results? In fact - doing simulations, there is very very little difference between diffraction limited aperture (Strehl 0.8) and perfect aperture (Strehl 1). Reports often indicate that difference is more than simulations say there could be, so I'm wondering about observer bias in all of that.