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I'd say you UHC is better than UHC-E at being UHC type filter (filter that passes major emission lines and blocks everything else). Only concern I have about UHC is IR leakage. We can't tell from above graph - but it looks like it passes light above 700nm. If 533 does not have UV/IR cut filter integrated (and as far as I can tell - it has only AR coated window) - you should use one just in case.

Isn't M16 emission type target? UHC passes all major emission lines - Hb, Ha, OIII, SII ... and reduces light pollution. Ultimately this should improve SNR.

This has nothing to do with actual focus. You are using very fast achromat lens - F/4.1 and it has a lot of chromatic aberration. You are also using ASI120mm camera - which is mono and only has AR coated window - no UV/IR cut fitler. This will make image extremely blurred due to chromatic aberration. This has zero effect on guiding as guiding is only concerned with star position and not how blurry the star is. In fact - guiding works if star is not in perfect focus, and sometimes if seeing is rather bad - it is better to slightly defocus star instead of having sharpest possible focus. As far as best possible guiding - well that depends on mount you are using. Small guide scopes with short focal length don't have enough precision for very precise guiding when wanted RMS is less than 0.5" or there about. But that is only achievable on very expensive and mechanically excellent mounts. Most of regular mounts won't be able to go below say 0.8" RMS or so. If you want the best guide resolution - then use OAG, otherwise - your guide setup is quite OK.

I still wonder why is calibration failing. How do you perform calibration in terms of math? Do you use 32bit numbers, do you create master with any sort of optimization - or simple average without rejection?

Nope, you are absolutely right. I was wrong to assume that it won't make much of a difference. I quickly created blank image with just a few hot pixels and made a measurement: It indeed shows that standard deviation is about 7.6 in this case. My logic was that standard deviation is calculated by dividing with number of samples - which in this case is 5496 x 3670 or 20170320 (about 20 million) - but forgot to factor in that what is being divided is sum of squares rather than regular sum. 14000 is rather high number and 14000 squared is even larger - 196,000,000

I don't think so. Although visually there is plenty of hot pixels - they are actually rather "sparse" - like less than 1 in 1000. For say 20Mp sensor - that would give roughly less than 20,000 hot pixels - visually that would clutter the image but it would only minimally impact standard deviation.

That is rather interesting. Stddev (avgdev) value shows significant distinction. Stddev is mix of bias (read noise + read signal) and dark current noise. It shows 8.6ADU in first case and 10.7ADU in second case. That would make dark current expressed in ADU around 6.366. Can you read off FITS header information? It should show black level automatically removed from raw file when converted into fits - at least FitsWork creates that Fits header - here is example of one raw file converted to FITS:

Can you do very simple experiment? I'm guessing that you used bias for calibration of both master flat and single flat of 20s exposure? Can you measure average ADU of that bias and also average ADU of 20s dark exposure. If these two numbers are significantly different - maybe try using flat darks instead of bias.

It is USB 3.0 USB type B plug B type plugs are often used for printers and in astronomy - camera connections.

Yep, that should be good way to do it. Don't forget to also remove bias (or rather dark as it is 10s exposure) for second sub. Emulate whole process of calibration although your light is actually just created with flat panel.

Yes, but it is best not to use individual flats used to create master flat. Best flat flat test is done when parameters are changed. Use one exposure length / light source intensity to create set of flats for master flat, then change parameters and take single or few additional flats. You can then try to flat calibrate additional flats (single or even stack of few) with master flat and it should leave you with uniform image (it will have some offset and some shot noise but it should not have visible intensity changes). Alternatively - you can exclude one flat from your basic set, use all others to create master and then flat calibrate selected flat with master created out of all others.

Two things 1. It is very very uniform although visual representation suggests it is not. It was deliberately done so to show variations in CMB - but picture itself does not show how tiny these variations are. If you look at color scale - it tells you magnitude of variations and it is +/- 500µK, or +/-0.5mK or +/-0.0005K Yes, that is 1/1000 of a single Kelvin 2. Although things were very uniform - in physics we don't have perfectly smooth things. Even vacuum is not empty / smooth - it is full of quantum fluctuations. It is the same thing here - CMB is image of quantum fluctuations at the time before inflation. When inflation happened those quantum fluctuations were frozen in moment and blown up in size to represent the grain we see (and other things contributed to this grain like baryon acoustic oscillations).

AZ-EQ Avant mount certainly can, but I'm not sure about StarQuest, although they do look remarkably similar. I'm sure they reuse a lot of parts between the two. I know that 130mm Newton and Maksutov 102 can't be collimated in these cheaper versions - they removed collimation mechanism. Not sure what else was stripped down. @Chris reviewed couple of these StarQuest scopes - even did some planetary images with ST102 if I'm not mistaken. Maybe he can offer first hand advice on choice of this scope.

As far as SW achromats go, there are two main lines - StarTravel and EvoStar. First is for fast wide field scopes - usually around f/5, while second is for slow achromats - usually around F/10 although there are some models that are F/7.5. StarQuest seems to be type of EQ mount. It is replacement for basic EQ type mounts - like EQ1 and EQ2. StarQuest line has 3 models as far as I can tell - Maksutov 102, ST102 and Newtonian 130mm. These should be considered beginner type scopes and are probably "light weight" versions of respective scopes - some parts being replaced with plastic and such - to save the weight and make them more stable on lightweight mount like StarQuest. StarTravel 102mm is the same scope as above StarQuest ST102 - but comes with tube rings and different accessories - depending on which version you choose. There is AZ3 mounted version - I would personally skip that one. If you really want EQ mount with ST102 - then look for EQ3 bundle. However, I think that short refractor like ST102 is better served by AZ4/AZ5 type mount (depending on whether you want slow motion controls or not). Slow motion controls are really not needed as you'll keep the magnifications low because of chromatic aberration - up to maybe x100 or so. ST102 is really wide field instrument and if you want a bit more general type scope that is still light and manageable - maybe check this out: https://www.firstlightoptics.com/evostar/sky-watcher-evostar-90-660-az-pronto.html It is a bit less aperture - 90mm but it has F/7.3 and that will enable you better views of the planets while still keeping scope relatively wide field (x20 vs x15 as lowest magnification with 32mm plossl - it will still fit most of Andromeda galaxy in FOV with that eyepiece)

Some of cameras have built in tilt adapter for just that purpose. Qhy one seems to have something similar. Does manual mention anything like that? Here is example from ZWO manual for their ASI model with same sensor: In any case - QHY model seems to have same set of front screws that is used to fix the tilt.

Hi and welcome to SGL. Tilt is really a spacing issue - but only hitting one side / corner of sensor. Astigmatic stars in right side of the sensor indicate that you have spacing issue on that side - while on left everything looks ok. That means that sensor is tilted. Often posted image (but I can't guarantee if it is 100% correct or applicable in your case) that suggests what is going on is this: That means that sensor is tilted so that right side is closer to reducer / flattener and left side is at proper distance. In any case - you should look into those tilt adjustment adapters.

Formula is rather simple: 206.3 * pixel_size / focal_length Pixel size is in µm and focal length is in mm. 294MC Pro having 4.63µm pixel size will give 1.74"/px with Esprit 100ED (F/5.5 - so FL 550mm, if I'm not mistaken), while with EdgeHD1100 it will give 0.34"/px Calculation is straight forward. Understanding it is a bit more complicated - and it involves an easy part and a bit more difficult part. First let's go with easy part. Resulting number represents how much of the sky is covered with a single pixel. Distances across the sky are given in angles (angular size) and angles are measured in degrees, minutes of arc and seconds of arc. Math that connects those is simple 1° = 60 arc minutes (denoted with ' so 60') and 1' = 60" (again seconds of arc or arc seconds is denoted with "). So 1° = 3600". Arc seconds per pixel helps you quickly convert angular size of object or FOV into number of pixels. Say you have galaxy that is 24' across. That is 24' * 60 = 1440" or 1440 arc seconds across. When you sample it at 1.74"/px using your Esprit 100 - that galaxy will be 1440 / 1.74 = ~828px across. When you sample it with EdgeHD it will be 1440 / 0.34 = ~4235px across. You can do similar calculations with your FOV - if you say have 1° FOV with esprit - what is that in pixels? 1° = 60' = 3600" = 3600" / 1.74 = ~2069px across. It can work in "reverse" as well. Since your camera has 4144px in horizontal - if you multiply that with 1.74"/px - you'll get ~7210" or about 2° (7200/3600 = 2). Indeed if you look at astronomy.tools with that combination - Esprit 100 and 294mc, you get that FOV is: It shows also 2° of sky. Ok, so that is easy part - how to convert angular sizes into number of pixels and vice verse. Now comes a bit more difficult part - that is under sampling / proper sampling / over sampling. That is very technical stuff so we need not get deep into it, but here are couple of simple "rules of thumb" that you can remember: 1. Coarser sampling - meaning larger number in "/px expression gives you better Signal to noise ratio for same aperture and integration time. In another words - if you have 100mm scope and image at 1"/px and 2"/px for an hour, 2"/px will result in better, less noisy image, but object will be smaller in the image because it will be represented by less pixels. 2. For any given image there is optimum or proper sampling rate - which simply means that detail in the image that depends on hosts of factors like seeing, mount performance, scope aperture and performance is properly matched to pixel size. Larger pixel size - coarser sampling or larger "/px number (but we call that lower sampling rate) is called under sampling. Smaller pixel size, finer sampling or smaller "/px number (which we call higher sampling rate) is called over sampling. Under sampling - is ok - nothing wrong with that, but object is not as large in the image as it could have been - image is less noisy Proper sampling - is ideal balance between captured detail and noise in the image Over sampling - is bad - it will not capture any additional detail because there is none but it will be noisiest of the three To recap: Under sampling and Proper sampling - good, Over sampling - bad How to know if you are over sampling or under sampling or sampling "real good" ? Well - you can't know until you already captured the image as every night is different - there are nights of good seeing and nights of bad seeing and that changes sharpness of the image. What you can do is figure out "average" sharpness of the image and then dial your sampling rate (or arc seconds per pixel) to match that. This brings us to third rule of the thumb: - scopes up to 70mm should not sample with sampling rates higher than about 2.5"/px - 80mm scopes should not sample higher than 2"/px - 100mm scopes should not sample higher than about 1.6"/px - 150mm scopes should not go higher than about 1.4"/px - attempt high resolution imaging with 8" or larger apertures on very good mount, and by high resolution imaging I mean ~1.0 - 1.2"/px. 99% of people will not be able to reach 1"/px in 99% of the time. You really need excellent scope, excellent sky and excellent mount in order to get image sharp enough to sample it at 1"/px In the end - there is simple relation between FWHM of the stars in the image and sampling rate. For given FWHM of stars in arc seconds - you want to sample at maximum FWHM / 1.6 sampling rate. Anything over that will result in over sampling and lower quality (this only applies to long exposure imaging and not planetary - that is another game and has different rules). If you are over sampled - like you are with EdgeHD 11" and ASI294 - you can bin your pixels in order to reach good resolution. That recovers SNR lost due to using smaller pixels (binning is like using larger pixels). With 0.34"/px - you can easily bin x4 to get to 1.32"/px (which in case of OSC camera means super pixel mode + software bin x2).

Interesting comparison, but not sure if it is representative of what both scopes can achieve? At least as far as Mak is concerned. It says in specs that x2 barlow is used on both scopes? ED120 is F/7.5 while Mak127 is F/12.5 scope (if I remember correctly effective aperture in that one is 118-119mm rather than 127?). With x2 barlow and ASI224, ED120 is properly sampled if bayer drizzle algorithm is used for stacking. Mak127 with F/25 is over sampled by quite a margin. If short exposures are used - this puts Mak at disadvantage, even with low read noise camera like ASI224 - overall stack will have lower SNR and so will individual subs. Lower SNR of individual subs makes it harder for software to properly align alignment points thus increasing motion blur somewhat over properly sampled version. Lower SNR of whole stack makes it less responsive to sharpening - or rather - noise floor is reached sooner. @Fedele Can you provide more technical details - like exposure time used in both cases, calibration applied, software settings used to produce image?

There is a link between three quantities: Megapixel count, sensor size and pixel size. In daytime photography we don't really think about limiting resolution and we don't really think of pixel size. In astrophotography - that should really be starting point - and next should be FOV. Once you set those two things - well, you don't really have a choice of pixel count - for a given pixel size and FOV - there is only so much pixels that you can fit inside.

I think it is down to people's perception more than anything. 14bit ADC is really no biggie. It is in no way restrictive and people happily image with 12bit ADC with cameras like ASI1600. As far as pixel size is concerned - well, I think that people are caught up in mega pixel craze. It is due to marketing departments of both mobile phone manufacturers and DSLR manufacturers that push large mega pixel counts as something very good. I think that 6µm pixel size of 2400 is just right for OSC full frame sensor. Such sensor is really suited to 10" or lager scopes. Say you have scope like that that is F/7 or F/8 - that will give it 1800 - 2000mm of focal length. Let's go with lower number of 1800mm. 1800mm and 6µm gives 0.69"/px - and because this is OSC sensor and we should really use super pixel mode rather than interpolation - actual sampling rate is twice that so 1.38"/px. That is very good sampling rate in my view. If you use 6200 with 3.76µm pixel size with such focal length - you'll get base 0.43"/px. That needs to be binned x3 or x4 to get good sampling rate. How many people actually does that? As you see, for someone with large scope that can illuminate full frame - if looking for OSC camera - 2400 makes sense - and they save money over 6200 as well. QE difference is rather small to be deciding factor.

Maybe because of people's perception of what is important in sensor? It has large pixel size (and everyone is chasing "high resolution" these days - so prefer smaller pixel size). It is "only" 14bit ADC while 6200 is full 16bit. It has slightly lower QE of the two - ~80% vs 91% People using full frame sensor are either using small expensive APO refractor that can illuminate such large sensor - and that means TAK for example - so I guess money is no issue there, or are using large reflector telescope like ODK / RC - and mono has edge there. First would rather go for 6200mc due to smaller pixel size, latter will probably go for 6200mm version. People with scopes that can't fully illuminate full frame will naturally go for APS-C size or 2600 model.

If you have the budget for it - 2600 is really the best option for OSC APS-C sized cooled astro camera.

Probably closest to that camera would be ASI071 https://www.firstlightoptics.com/zwo-cameras/zwo-asi071mc-pro-usb-30-cooled-colour-camera.html Newer, better sensor (with smaller pixels) and more expensive: https://www.firstlightoptics.com/zwo-cameras/zwo-asi-2600mc-pro-usb-30-cooled-colour-camera.html Both of these have APS-C sized sensor - so FOV will be the same as your 1100D.

Did he give exact reason why? What won't work if there is no saturation / clipping in camera?

Does it matter that pixels won't saturate? You can impose artificial saturation and clip pixels yourself at say 50000ADU? Most of the time that is what is happening with hard saturation limit - real values are clipped either because of e/ADU and bit depth or they are clipped in firmware. Pixel full well capacities are probably not very even due to manufacturing defects and maybe in this gain range - there is simply no clipping but you are rather reading out actual full well of each pixel. Uneven flats are not issue if flat fielding works. I also have very strange pattern in Ha with ASI1600 and Panasonic sensor. It's sort of checkerboard pattern - however, flat fielding works very well regardless. Why is it that yours is not working? Have you tried flat/flat correction? That would be - take a set of flats of one exposure length, take set of flats of another exposure length and correct first master with second master (do add flat darks for proper flat calibration).