vlaiv

What scope is that? If you have rotation between camera and filter - you can rotate scope in rings and again rotate camera so that it is properly oriented - that way filter drawer will not point towards dovetail bar?

If you zoom past 100% - all images are going to show artifacts. Point is - don't zoom beyond 100% unless you want to see artifacts. It has nothing to do with under sampling. Look at these: Top is nearest neighbor resampling, bottom is much more sophisticated resampling. Blockiness is not feature of under sampled image - it is feature of nearest neighbor resampling when you enlarge image. But you don' need to enlarge image using that algorithm - you can use B-splines or Mitchel or similar resampling method and get very nice looking smooth image (without much detail - after all you did zoom in 300%).

I understand that - but how can you tell? Do you think that this image is under sampled and why? It is, by the way, sampling rate is 5"/px and it was taken with 8" telescope, but I'm wondering what in the image would make that obvious?

7nm - Baader Ha filter for DSO

What do you think will be noticeable effect of under sampling? I think that you'll be just fine with 6.5µm pixel size and Samyang lens if you do super pixel mode.

Just checked - sensitivity difference seems to be 2-3% in regular Ha

Maybe you could just extract PRNU information with DSO Ha filter and flat panel?

Ah yes, I have that on my ASI1600 as well. I did not notice that on my ASI178 because I did not do narrowband imaging with it and it is color sensor so it will have bayer matrix anyway - but it is there on ASI1600 as well. For DSO imaging - it can easily be solved with flats. Here is 1600% (nearest neighbor resampling) zoom of my master flat for Ha (DSO kind - not solar): Can't you fix that with flats?

I'm trying to find the thread you are referring to - but failing. Not sure what issues with FPN are you having? I experienced both PRNU and Telegraph type noise with my ASI1600. I also have ASI178mc cooled version. What should I be looking at? Looking at master dark from this camera - there are vertical and horizontal bands - but I did not notice those in final images - I guess those calibrate out? That is my master dark binned x6 and insanely stretched.

I guide with OAG with the same guide resolution - 0.48"/px native and 0.96"/px binned (3.75µm and 1624mm). I regularly use bin x2 without loss of guide precision.

Yep, it is under camera settings - noise reduction: 290 has small pixels - 2.9µm I believe? You'll probably want to bin them then. There are few options - 2x2 bin, 3x3 median. I think that 2x2 bin is the best one. Even binned - you'll have plenty of guide resolution. You probably want your guide resolution to be at max 2"/px. With that pixel size you only need 300mm of FL and I'm certain your scope has at least twice that if not much more (is that 8" f/6 on EQ6 there?).

Most likely it is differential flexure. I think you'll find OAG every bit as easy to use as guide scope - with added precision and lack of problems such as flexure. Only mind the spacing to avoid prism to stop down your aperture for guiding and depending on what guide camera you are using - you can select bin x2 in PHD2 - it will again improve SNR of guide exposures.

Notice that you have 0.45" and 0.47" in RA and DEC. When these two values are so close - I think that is sign that you are seeing limited. Bumping up exposure length to 4s or so does help in such cases. Belt mod is certainly worthwhile upgrade, it can only help. I switched to ASCOM driver instead of native for my guiding. That achieves much better SNR values. Not sure what your guiding resolution is (guides cope and camera), but it might help a bit with centroid precision.

It was actually 8" from a dob - longer tube than 200P. 200P is F/5 - this was F/6. Don't have very good images of that setup, but here is one: Needed 3 5Kg CWs to get it balanced On the other hand, 8" RC is much more compact and this setup: also has close to 12Kg - that is ST102 side by side with 8" RC - but only two CWs needed to balance it (just - both on far edge of CW bar ). I now regularly image with 8" RC and OAG - that is about 11Kg or so. Scope itself is 9Kg, I have 1Kg counter weight to balance it in DEC (it is very back heavy) and camera, oag+guide cam and filter drawer on it with no problems. But I did mod the mount extensively since - I replaced puck and dual saddle - vixen + losmandy, mount is now on Berleback planet tripod. That adds quite a bit to its stability.

Indeed, my bad ...

Do note that it is just a guideline and much depends on size of the scope as well - length in particular. I happily image with 12Kg+ on Heq5 - but it is compact scope - I tried to do the same with 8" F/6 and things were far from good.

Hm, seen this?

I can't tell anything except that I would consider it for myself if I had the need / funds for it. Haven't read or heard of any experiences with that particular model, but it does look to be quite ok scope.

2/3 of 15kg is very close to 11kg 2/3 rule applies to visual in order to arrive to sensible limit for imaging. With 15/11 that is already calculated for you.

Maybe this: https://www.teleskop-express.de/shop/product_info.php/info/p12878_TS-Optics-CF-APO-102-mm-f-7-FPL55-Triplet-APO-Refractor-with-Certificate.html together with this: https://www.teleskop-express.de/shop/product_info.php/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html Or maybe even M82 version of Riccardi flattener (larger and corrects for full frame if that is of use)

I'm not sure how that happens unless you use nearest neighbor resampling method and then zoom in (solution - use other resampling methods and don't zoom in ) Depends how you process your data. In principle - OSC camera really samples at half the sampling rate of mono camera and if you use super pixel mode for example to debayer your data - you'll get image as using pixels twice as large (sampling rate halved). If you use bilinear interpolation when debayering - you are not doing anything clever and it is the same as trying to get resolution by enlarging the image (again using bilinear interpolation) - you'll get larger image but not detail. Only time when OSC camera can approach Mono in resolution for the same pixel size is if you utilize bayer drizzle for stacking. Unlike regular drizzle where one "assumes" pixel is smaller than it is (or better word is "pretends") - here we actually have "smaller" pixels - smaller in comparison to sampling rate. For that reason bayer drizzle is capable of providing almost the same resolution as mono sensor. You data needs to be properly dithered to do that. In any case - difference between x2 sampling rate is not that big as you might expect, especially when you are close to optimum sampling rate. Here is example of twice lower sampling resolution vs original. I took original image that is already under sampled and then I reduced it x2. I then enlarged back that smaller image and created blink animation with original image. You can see in smaller stars that some of sharpness is lost but in reality - not much of the detail is lost - at least not as much as you would expect (twice lower sampling rate sort of leads us to believe that there will be only "half of detail" - but that is not true). With over sampled images - this difference is even less noticeable (in fact with over sampled images - you can get proper sampling by halving sampling rate - but even if you move from over sampled to under sampled - difference will be very small).

Ok, yep, this is good comparison of what diffraction limited optics produces at these sampling rates: 80mm diffraction limited optics at 4"/px - same target: We could argue that 4"/px is under sampling for that image - but I still don't see any blockiness in there.

I'm saying that lens is not even diffraction limited - in fact far from it. Samyang 135 F/2 has aperture of 67.5mm. In order to exploit 67.5mm F/2 diffraction limited optics - you need 0.5µm pixel size. I would really like to see example where you see blockiness in image with 6.5µm pixel size and comparison to 3.75µm where you feel that sampling rate made big difference. Here is what green channel of 4.8µm pixel size on Samyang 85mm F/1.4 lens stopped at F/2 looks like: To my eye - that image starts to be properly sharp at about 1/2 - 1/3 of that resolution: which equates to 9.6 - 14.4µm pixel size. Mind you 85mm is not much worse than 135mm in terms of sharpness: at least with sensor size I was using - diagonal less than 9mm, so distance from center is less than 4.5mm

Thing is - you are not under sampling. I'm guessing you are using Samyang 135mm, right? This is published chart by Samyang - even at F/8 - 30 lines/mm gives something like 95% contrast. 30 lpmm corresponds to pixel size of 33µm - you are using 3.75µm pixel size - almost 10 smaller. When I was working with Samyang 85mm lens - also very sharp - it too can't handle pixel sizes that small. I calculated that good pixel size for such lens is about 10-12µm. In another words - you'll see no difference between mono and color data. Only difference mono can make is using narrow band filters. Even then, lens is not diffraction limited but it is much closer to that performance.

That one looks like it might be adjustable for distance - at least you can slide it up and down EP barrel. I've got one of these: It is attached to the top of EP and does not have height adjustment.