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I know of another example of silly looking white tubes - wide at one end, narrow at the other, about two meters tall that have very high price tag - it looks it's nothing uncommon

Not really sure if this is valid test. Have you seen screen pixels under magnification? Most displays have it like that, but some have it in different configuration, like this: Green carries the most brightness out of three R, G and B colors and in above image - there is greater separation between vertical lines then horizontal lines with respect to green light alone (as pixel is vertical triplet).

This one is even better for showing effect (at least on my screen): http://www.lagom.nl/lcd-test/sharpness.php When I scroll this page - chart "flickers" all over the place

There might a bit of that, but I believe that dominant effect is screen flicker when scrolling. Check out this page: http://www.lagom.nl/lcd-test/clock_phase.php When you scroll it, depending on your computer screen it might flicker quite a bit.

Btw, interesting fact - if I open image in another tab, I can't see it with my healthy eye, but I can with my far sighted / highly astigmatic eye (without glasses).

While not the best example - depends highly on computer screen calibration, it is very good example for what it is supposed to show. It's not the point in looking at it like this, on SGL. Point is to open the image in another empty tab. That way it will be shown full size (about x3 the size of the image embedded here on SGL) - try seeing 17 on that image! If you can't - then you need to slowly step back from the screen until you find size (magnification) that will yield the most contrast. Scrolling is cheating by the way - Many computer screens "flicker" when scrolling high frequency signal. It has to do with gray to gray response time of computer displays.

I wanted to try color calibration of my ASI178 and finally came up with a "sensible" technique. Usually, when color calibrating for certain lighting type, photographers use "colorchecker passport" or similar color chart. These are basically printed colors of known RGB values and color calibration consists in shooting this chart and then adjusting color balance in post processing to get as close to known RGB values. I wanted to do something similar, but these charts are rather expensive - about $100 or more online. There are Chinese knock offs that are cheaper, but I did not want to spend any money on it since it won't be a thing I regularly use. I finally came up with idea - one can download similar color chart online. I just need a good display device capable of rendering very small image of it that is of a good color accuracy, hm what could that be? Enter my cell phone. I've got Xiaomi Mi A1 and it's got pretty decent screen - 5.5" LTPS IPS panel and colors look rather ok on it. Just a bit of math and I was set to go. Phone is to be placed about 10 meters from telescope. I'll be using my Mak102 and ASI178. Field of view at astronomy tools was used to quickly calculate FOV in degrees (0.33 of a degree in horizontal), and this calculator for distance required: http://www.1728.org/angsize.htm I made image of a color chart on screen be about 5cm. Here is used template: My phone renders it pretty much the same as my Dell U2311H except that colors are very slightly more vivid - in particular blues and it looks like overall color temperature is just a bit cooler. This is probably due to LED back light on the phone display. There differences are so subtle that they are barely noticeable and smaller than differences we are about to see below. So I went and recorded couple of frames with SharpCap using ASCOM driver instead of native. Here is what came out of the camera as raw data directly mapped to RGB: Colors are obviously wrong because image has not been color balanced. First logical step would be to color balance the image using simple ratios for R, G and B channel: Luckily bottom row is full of gray values so that is rather easy to do. Notice that most left bottom square is clipped. This is because I clipped green on that square (only on that one) due to saturation and I did not notice when I was shooting. Colors don't look quite right like in above chart. Gray gradient is not as it should be and colors are too dark and saturated in comparison to reference. This is because colors are still linear and sRGB that these images are recorded in, requires gamma of 2.2 to be used (in fact it's a bit more complicated gamma function but for this test, gamma 2.2 is good enough approximation). Here is simple color balancing encoded in sRGB with gamma 2.2: Well, this is better - gray gradient is now uniform, but colors are still not quite as they should be. How do we fix this? It turns out that best color conversion is not simple channel balancing, but rather applying color conversion matrix. This is the same as color mixer where each of output channels depends on all three input channels. I thus opened Libre office calc and did some measurement on reference image and recorded image and derived transform matrix: new red = 1.3516376483848*r+0.033549040292064*g-0.054423382816904*b new green = -0.619460118029851*r+1.2330224800277*g-0.211822127381072*b new blue = -0.178260528770039*r-0.088350168915713*g+1.19254273096779*b You don't really need that much decimal digits - I just copied numbers from office calc and it gave me that precision. Once you do this matrix transform on linear data and do gamma correction, this is what you get: Colors are now the closest to reference image, maybe blue and red are just a tad over saturated, but I believe that is because of my phone. With this new color conversion tool, I set to check it in action. I shot Jupiter some time ago and of course, raw image from camera desperately needed proper color balancing: Too green and all wrong, right? Auto color balance function of Registax gave me this (and processing of course): But I had a sense that colors are too washed out and need a bit more saturation. This was even not gamma corrected. This time, I thought I give it a proper color treatment to see what I would get, and result is somewhat disappointing. Why would I get completely wrong color here? And then I realized. Jupiter is low now and atmosphere has this strange property - it makes sun orange/red when setting, although it should be white/yellow. No wonder Jupiter has such strong yellow/orange cast as well. Transformation worked perfectly and gave actual color. In fact, If you observe this image in complete dark without any other white surface, after some time it will start resembling view of Jupiter at an eyepiece (eye will try to color balance image and make it slightly whiter but it will still remain pale/yellowish). In order to correct color so that planet looks like it was shot outside atmosphere I'll need to account for atmospheric impact. I'll be thinking about how to best do that.

Indeed, I wish for larger sensor as well since ASI1600 is only 4/3 format.

Price is very low at ~150e, and if tube is good it would be worth it. However, like @John already mentioned - diagonal mirror is exposed to dust and missing top part. That top part is together with the 25mm eyepiece in one of the images - meaning it was screwed off - something that regular telescope owner would never do. Finder is mounted other way around and what worries me the most - there is no single image of optics. Can you inspect the scope in person, is this second hand item somewhere near you? If so, it might be worth to get it for the OTA alone. Working mount would be a bonus. Don't get AZ3 as it is not very good mount for astronomy. It is much better for terrestrial observation. Get AZ5 instead or if you can AZ-EQ Avant is really interesting mount - it can be used in AZ mode for simplicity or EQ mode for planets and simple tracking. It also can be upgraded with tracking motor rather cheap.

Your amp glow does not calibrate out? Mine does without any issues. Whole ADC / FW thing and dynamic range is thing of perspective. What if I told you that ASI1600 is camera that has 64K full well capacity, 16bit ADC and 6.8e read noise? Suddenly it does not look nearly "as bad" anymore, right? But how to turn ASI1600 in such camera? Let's say you want to do 15 minute subs with such camera, what should you do? Well, take 16 frames 56.25s long (unity gain) and stack them (sum stack) and result will be the same as if you used 64K FW, 16bit ADC, 6.8e read noise camera and took single 15 minute sub. If you dither, there will be added bonus with calibration and noise "smoothness". Here is very simple explanation for what is going on: Imagine you have number in range 0-3. You need two bits of information to store that value. Now look what happens when you add two such numbers: if you add 0 and 0 you get 0, but if you add 3 and 3 you get 6. Lowest number that you can get as a result is 0 while highest is 6. Result is therefore in range of 0-6. That is 3 bits of data (0-7). Now, if we add 4 such numbers, result will be in range of 0-12, which is 4 bit value (0-15). If you add 256 such numbers, result will be in range of 0 - 768 - which is 10 bit value (0-1023). And so on .... (there is small under utilization of the full bit range that depends on how many values you add). Noise adds in quadrature, so read noise of 1.7 added 16 times will be sqrt(1.7^2 * 16) = 1.7 * sqrt(16) = 4 * 1.7 = 6.8e.

Why do you feel your ASI1600 is rubbish?

I'm not sure it is only couple of months old. Ad says it is on EQ2 while images show EQ1 mount. Skywatcher has not been making blue telescopes for many years now, it is even very hard to find blue tube Mak102 images online. If you can, get it on AZ-EQ avant mount. It should not be much more expensive than that model you found second hand: https://www.firstlightoptics.com/sky-watcher-az-eq-avant/sky-watcher-skymax-102-az-eq-avant.html?currency=3 ($360 at FLO - not sure what your import tariffs are).

But how do you take into account duration of the flat and mean flat signal level? If you for example have camera with 7k pixel well and you have another camera with 57k full well capacity. Both of these have their flats taken at 75% histogram peak. Single flat of first camera will have SNR of ~72.45, while single flat of second camera will have SNR of ~206.76. Scale both flats so that signal is 1, noise will be very small. In case of first camera, although bigger, noise will be ~0.0138. This value is very small, but how does it impact SNR of image? Let's say that signal in the image is 1e and it is perfect signal - no noise. We need to correct it with above flat. We will have: 1 / 1 +- 0.0138 => 1/0.9862 to 1/1.0138 => 1.014 to 0.9864 This is 0.014 above 1 and 0.0136 below 1. I'm showing you this because this is no longer symmetrical distribution - it is no longer Gaussian and you can't add it like Gaussian (or Poisson) distributions if you are not sure it will work like that.

Hi and welcome to SGL. I don't know much about Levenhuk scopes, so I can't say if that particular model will be good or not. What I can do is tell you a bit about my experience with Skywatcher 102mm Maksutov. You will see good detail on the planets and the Moon. It is lovely sharp scope. In fact, here are images of planets taken with this scope (mind you, images at eyepiece will never be this sharp as this was processed 4-5 minute recordings that picked best frames from camera and then sharpened - but you can get the idea of what the scope is capable of): Mak102 is nice little DSO instrument as well. Many people say that you have narrow field of view with it - but I don't think so. It is 1300mm of focal length and that is just a bit longer than 1200mm focal length of 8" F/6 dobsonian - no one will ever complain of that scope being narrow field of view (and field of view depends on focal length of telescope). It will show you bright DSOs and some not so bright ones. For example, just a couple a days ago, I was out observing with some friends. We had 3 scopes with us 8" f/6 dob, this little Mak and another 4" scope - Skywatcher ST102 - refractor. Mak showed pretty much the same image as ST102 on brighter targets like M13. Maybe even slightly better image. I managed to see NGC7331 with it as well - which was rather big surprise for me. With 4" of aperture you can see a lot under dark skies (and we were observing in only Bortle 4 and it was not that transparent).

If you have stock EQ6 that is about what you will get at best - 0.8" RMS. Its not down to seeing, it's down to mount performance. If you suspect that seeing is problem - try longer guide exposure to see if it changes anything. Btw - acceptable guide RMS is the lowest one you can get with your setup . It always impacts final result in negative way. It needs to be quite a bit smaller than other factors to be "masked" by them. Guiding error half the size of seeing error will act as if seeing error was increased by about 12% and guiding error was 0. We can say that when guiding error is less than half that of seeing it starts being "masked". Only problem is that you must match "units" for this calculation. Guiding error is in RMS while seeing error is in FWHM. There is conversion factor of ~2.355. This means that when seeing is 4" FWHM you actually need 4" / 2.355 and then half of that in guide error - ~0.85" RMS guide error. You always want the best guiding you can get really.

Primarily high fps. Planets fit nicely on 640x480 as they are small. Moon is exception and it likes larger resolutions - but not too large with your scope which has coma. If you use too large field of view, the Moon will be blurred at the edges of the frame due to coma from Newtonian telescope.

Hi, welcome to SGL. Planets and stars move across the sky. This is due to earth's rotation about its axis. Your camera is probably pretty solid - but things simply move out of the frame because - well, they move all the time. Not everything is moving at the same rate though and the time it takes for it to leave the frame depends on focal length - as you've noticed. In a nutshell - this is what happens. Sidereal rate is about 15 arc seconds per second. Arc second is very small measure for angles - 360 degrees in full circle, 60 arc minutes in one degree and 60 arc seconds in one arc minute. Depending on the size of your sensor and focal length that you are using - you can calculate how fast things will move out of the frame. http://www.wilmslowastro.com/software/formulae.htm#ARCSEC_PIXEL For example - Canon 750d with 200mm lens will be at 3.82"/px. It has 6000px across the sensor, so that is 6000 x 3.82" = 22920" If we center planet and then let it drift - it will drift for half a field of view or 11460 arc seconds. At speed of 15"/s it will take 764s for it to drift out of FOV. This is strictly true only at celestial equator. Once you start moving in declination (towards Polaris) - this apparent speed drops with cos(declination) factor. At declination 60 degrees it will only move at half this speed - ~7.5"/s. In any case, if you want this to go away - you need an astronomical mount that can track for you. In particular you want something called equatorial mount. There are very nice compact - star tracker type mounts that will track the stars for you, like this one: https://www.firstlightoptics.com/skywatcher-star-adventurer/skywatcher-star-adventurer-astronomy-bundle.html What focal lengths do you use and what do you want to image?

What does this mean? I don't really follow your equations. How do you represent following: Let's assume we have a perfect flat that corrects vignetting of 70%. It will divide image in that area with 0.7. All components get divided with 0.7 (what ever remains in single sub at point of flat calibration) - signal gets divided and all remaining noise sources get divided with 0.7. I don't see that example in your above formula.

What is your background value in electrons from that sky? Although it is very dark, if you are shooting wide field / low resolution - large part of the sky will be covered by single pixel and pixel values from the sky will still be higher. High resolution work on the other hand spread sky background over more pixels thus lowering each value.

You can build very high dynamic range image with even 8bit camera - you don't need large DR in single exposure - that is what the stacking is for. It is feasible way of doing things with modern CMOS cameras because they have low read noise and therefore can utilize short exposures in LP areas. Otherwise you loose more than you gain by not using multiple exposure lengths. Whenever you stack certain number of frames - you extend dynamic range by log base 2. Stack two frames - your data range went up by one bit. Stack 16 subs - it went up by 4 bits. Stack 256 subs - it went up by 8 bits and so on. If you want to capture very big dynamic range - trick is to stack many short exposures. Each short exposure won't saturate sensor and enough of them will make final image very high dynamic. Problem with this approach is read noise - which is per exposure - you inject a lot of it. It has to be really low and smaller than some other noise source (usually LP noise is a good candidate) in order not to matter much.

SW star adventurer is simple star tracker - it's like a "clock" device - it does not move in DEC and has no goto capability. It also can't be guided. You do good polar align, let it track and shoot exposures. If your working resolution is low and polar alignment is good - you should keep most of your frames (there will still be some periodic error in that mount). AZ GTi is really easy to setup in EQ mode. You need three items: 1. Wedge. There are couple of them available: https://www.firstlightoptics.com/skywatcher-star-adventurer/skywatcher-star-adventurer-equatorial-wedge-white.html https://www.firstlightoptics.com/william-optics-mounts/william-optics-wedge-and-extension-bar-for-skywatcher-star-adventurer-and-ioptron-skyguider-pro.html https://www.teleskop-express.de/shop/product_info.php/info/p7929_TS-Optics-ATC-Wedge---Mini-Equatorial-Wedge-for-Giro--AstroTrac--photo-tripods.html https://www.teleskop-express.de/shop/product_info.php/info/p11485_iOptron-Polar-Wedge---base-for-SkyTracker-Pro-and-for-many-tracking-mounts.html There is not much to it. AZGti has photo thread at the base and so does every one of these wedges - so you just screw it on and you are ready to go. 2. Suitable CW bar and counter weight. Most people adapt this one: https://www.firstlightoptics.com/skywatcher-star-adventurer/skywatcher-star-adventurer-counterweight-kit.html There is a problem with particular CW bar - it has M8 thread (I believe) and AZGti expect M10 or M12, so you need to purchase suitable male to male adapter. see here for details: https://www.cloudynights.com/topic/631581-sky-watcher-az-gti-mount-counterweight/ Or here (it also says you can use EQ1 counterweight bar and counter weight and there is offering from TS as well): 3. You need to flash your firmware to latest version. This is rally really simple to do - it took me something like 10 minutes to do it. It is also useful in AZ mode if you observe with your left eye as it changes scope orientation from mount on right to mount on left. http://skywatcher.com/download/software/motor-control-firmware/ You need firmware loader (one that uses wifi) and AZ/EQ firmware for AZGti "Firmware: AZGTi Mount, Right Arm, AZ/EQ Dual Mode, Version 3.20" I used my laptop - just powered the mount, connected with laptop to access point it created, started loader and loaded the firmware. Btw - you need to take into account disclaimer given by Skywatcher: If you are experienced, want to explore and have fun - then go for it Given the above - chances of bricking the mount are very slim. Only serious DIY that comes to mind would be tuning the mount for backlash and such. Here is some info on that - just so you put things into perspective as some people complained about serious periodic error and backlash. My mount has quite a bit of backlash and I intend to do this before I start fiddling with EQ mode (I've done the firmware update but am yet to get wedge and CWs myself). https://www.cloudynights.com/topic/668785-adjusting-backlash-on-skywatcher-az-gti-mount/

Out of interest - how did you model flats contribution as it is modulatory rather than additive (it impacts other noise sources not only with noise but signal value as well - both flat signal and target signal - there are cross terms that will be "noise").

So I've heard: Mind you, I've have had that barlow and did not do measurements of how much magnification it gave. Also - my sample was not as good . Cemented pair was not properly cemented together - there was something like 1/4 of mm of decenter and that produced chromatic dispersion at very high power. I used it as ADC one time because it countered atmospheric dispersion perfectly

How about simple tracker like SW adventurer? Or perhaps, something similar to your ideal mount - just a bit less precision and less carry capacity https://www.firstlightoptics.com/skywatcher-mounts/sky-watcher-az-gti-wifi-alt-az-mount-tripod.html You can use that mount both in AZ and EQ mode, but EQ mode requires a bit of fiddling and few more pennies spent. You'll need EQ wedge, Counterweight bar and counter weight and flashing firmware to version that supports EQ operation. I have that mount and have used it AZ mode so far. I think I'll tune it since there is quite a bit of backlash (there is tutorial on how to open and adjust this mount). It can be guided and I think it's supported by EQMod (with custom settings). You can place it on photo tripod of your choice - so you can find a very light weight one ...

From what I can see - they only quote their own line of eyepieces - probably because you can use those without the need for adjustment. Ideally, every eyepiece out there should have focus point at eyepiece shoulder. That would make every barlow work at prescribed magnification and every eyepiece would be par focal. In reality this is not the case, and eyepieces often require refocusing. I don't own any Tak eyepieces but it might well be that they were careful enough to put focal plane at eyepiece shoulders?