vlaiv

It really depends if you want to capture color or not. I think that for planetary imaging, OSC is much simpler than having filters and filter wheel - with exception of motorized filter wheel and motorized focuser - with software that can remember focus offset for given scope. That can amount to quite a bit of expense there. ASI178mc is not slouch either. I've taken this image of the moon with ASI178mc and Mak102:

First check orientation of elongation and see if they align with RA or DEC. Compare that to your guide log (if you have it) and see if there is possibly something in the guiding that will cause these. Also - see if it could be flex. Best way to check for flex is to see if there is constant drift between subs (compare star positions over multiple subsequent subs). In the end - check collimation.

It does look alike that thing in the image. I still think it is unrelated - but I could be wrong.

With scope focused at infinity - there should be no way for any pattern located at aperture to be anywhere near focus - it should be all blurred. Even if it was pattern - two successive flat exposures should have been the same and should calibrate one another properly.

I don't think so, but worst I've been to is about -6°C and all my gear was fine.

Well, something is wrong with your flats. I can't really understand what exactly - but if I take any two flats - they don't correct each other properly. When dividing one flat exposure with another - result should be just more or less uniform noise - this is what I get: if I use two flats from second batch and this: If I use two flats from first batch. You say that you've been using some sort of cloth over objective? Did you by any chance change focus position between flats and lights? What is difference between flats marked as 9.40 and those marked as 10.50?

@Newforestgimp What software did you use for capture and did you adjust any sort of "white balance" controls in that software?

It suggests that there is not much difference between say -15°C and -10°C and you should use what is convenient. In warmer weather it is harder to reach set point - and that depends on your deltaT. If your deltaT is say 30°C - and it is 20°C outside - you'll struggle to get it down to -15°C.

I think it is something to do with processing. Aside that those stars are funny shaped and somewhat large - they are processed in the way I would not expect and that seems to be the trend - they look "flat" as if they don't have a core. Look for example this: That star has brightness "stopped" somewhere around grey - like you did not want that star to shine and be bright. That star is very bright - yet brightest pixel is something like 170/255. Skirt / halo and spikes around the stars should be faint - yet they are equally bright. That sort of makes flat appearance.

I like bigger scopes as it usually leads to (potentially) faster system. Although there is this notion that F/ratio of telescope is what determines the speed of system - that is not quite correct, and I like to view it like this: Speed of the system is aperture at resolution. Given certain resolution - or sampling rate - larger aperture simply wins. Problem starts when people try to compare two different apertures at two different resolutions. There is way to compare those as well - but it is a bit more involved. If you don't change camera and just go for larger scope - in this case slower scope in terms of F/ratio - well, you'll get slower capture. Another thing to consider is if scopes are diffraction limited in the first place and will there be some resolution improvement in if you switch the scopes. 8" scope at 400mm focal length will have diameter of airy disk of 2.5µm In my view pixel size of 3.75µm of ASI2600 is simply wasted on RASA - you need to bin x2 at least. RASA11 is corrected over larger field compared to RASA8 - that might be important for ASI2600 sized chip - which has diagonal of 28.3mm, however - there will still be a need for flat fielding which is not very feasible with RASA systems At 11" F/2.2 Airy disk is 2.7µm - so again not diffraction limited and need to bin at least x2. I'm not very big fan of RASA scopes for imaging, so I can't really advise properly - but for me it really comes down to FOV - do you like FOV of RASA8 or would you like slightly smaller FOV of RASA11 while keeping same number of pixels in the FOV without oversampling (~3000 x 2000 px)

Not seeing it I appreciate people don't really zoom in to see their data at 100% - but if you are going to post it at full resolution - well, then don't be surprised if people want to look at the data at 100% in order to see smallest detail capture.

What happens to the stars in the processing? Why do they end up like this:

Difference between 1/50s and 1/7s is very small at -10°C according to this: Even if doubling temperature is ~5°C - that would mean 0.00128K/px/s - or really negligible value at 1/7s I suspect that it is bias instability that is the issue here (higher bias value than flat dark). I'm downloading subs and will inspect bias vs darks to see if I can find something useful.

See this thread: https://www.cloudynights.com/topic/614178-new-224mc-settings-for-firecapture/ Especially post #7 - by Torsten

I think you can actually extract raw (or close to) raw with DCRaw and choice of color mode. Have you tried that?

That really depends. My take on it is that those are not to be touched in capture phase and color should be corrected in post processing. If you however don't perform post processing and want to say show someone live view, then you can adjust white balance like that. Actual settings will depend on what are you trying to achieve. Say you want to image an object under yellow light (street lamp or incandescent bulb) but want to show colors as object would appear in daylight / when color adapted - then you would move sliders until you get white color on object - looking white on screen. Color correction is very complex topic and can be performed differently depending on the effect you want to achieve. For simple use cases - you can use white balance sliders, but for more complex - I advocate proper color calibration.

In general - reflections are less pronounced if there is larger distance between reflecting elements. This is because reflection is unfocused light - usually from bright star and if you spread it over larger area - it's intensity goes down. Large enough reflections fall below noise floor and can't be seen. It is a bit like dust shadows - close to sensor they are very "black" in flats - and those further away are greyish and sometimes not that noticeable. As far as impact on your particular setup - I won't hazard a guess of how it might behave. Maybe best thing to do is get filter from retailer with good return policy and then just try how it behaves on your setup?

Like the solution, but completely baffled by this detail:

You can use x3 barlow to get in closer - but there is simply no point in doing so. Amount of detail available is limited by aperture of the scope and above formula for F/ratio versus pixel size takes that into account. Detail depends on aperture and focal length with pixel size determines how zoomed in you are - F/ratio is ratio of focal length and aperture - so everything is taken into account. With stronger barlow - you would get more zoomed in image - but without detail - same effect as like imaging with x2 barlow and then resizing image in software. When you enlarge image in software - image is larger but no additional detail exists in the image. On the other hand - using stronger barlow causes issues with signal to noise ratio because light is spread over more pixels and each pixel gets less light because of that (there is only so much light that is gathered by any scope). This means lower signal and in turn lower SNR. With planetary imaging SNR is important because it lets you sharpen image without making it too noisy. Using x3 barlow would therefore - make larger and more noisy image without additional detail and is not advisable.

That somewhat deepens the mystery - I was convinced it was down to filter placement, but think I can't explain this - except that there is difference between 2" and 1.25" version of filter?

Filter is probably threaded onto 2" filter thread of flattener?

That is down to color calibration. CCDs don't produce accurate colors either - but are closer to real colors when color calibration is not performed. DSLRs perform color calibration internally because people expect accurate colors from their daytime images. In order to produce accurate colors - one needs to create color transform matrix and apply that to raw linear data to produce linear RGB data. Then in order to maintain that color information - images need to processed in certain way. Almost no one is doing that in astrophotography. When we stretch data we usually desaturate it a bit with that stretch - and that is why people end up boosting their saturation. For example - here is DXOMark Canon 750d specs: https://www.dxomark.com/Cameras/Canon/EOS-750D---Measurements That is color matrix that produces accurate colors from RAW values for this camera. When using dedicated astro camera - you get RAW values that need to be converted to sRGB tripled values for accurate color rendition.

Never mind scope - what size of filter do you have? I just had a look at Astrobin and images are produced with 2" version of filter. This means that filter is used in front of any corrective optics - like field flattener. 1.25" version is usually used in front of sensor and between sensor and field flattener - that might be the issue.

What scope are you using those with?

Not sure if this is limited to 294mc camera. That camera is sort of sensitive - people had issues with flats before (but that was down to how they were taken - flat assistant in APT did not work well).