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Old 08-03-2021, 11:24 PM
DIYman (Doug)
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To bin or not to bin????

I am looking at mono astro cameras and have become aware of under and over sampling issues. Getting a camera that has the correct pixel size (9um) for the focal length of my scope is proving difficult (2250mm). A problem is the trend to smaller pixels (<5um) which I suppose reflects the current market which is based on the small sized imaging scopes used extensively. I guess one solution is one of these camera and then simply bin 2x2. Apart from loss of resolution, are there any other downsides I should be aware of?
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Old 09-03-2021, 07:04 AM
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gregbradley
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Quote:
Originally Posted by DIYman View Post
I am looking at mono astro cameras and have become aware of under and over sampling issues. Getting a camera that has the correct pixel size (9um) for the focal length of my scope is proving difficult (2250mm). A problem is the trend to smaller pixels (<5um) which I suppose reflects the current market which is based on the small sized imaging scopes used extensively. I guess one solution is one of these camera and then simply bin 2x2. Apart from loss of resolution, are there any other downsides I should be aware of?
Yes that is what I do, bin 2x2 on a longer foal length scope. The QHy600m has 3.76 micron pixels so binning 2x2 gives the equivalent of 7.52 micron pixels which at 2000mm focal length is .77 arc secs/pixel. Which is a bit oversampled but not by a lot and if you have reasonable seeing it will be fine.

Using 1 arc sec/pixel as close to ideal with average seeing.

There is the full frame 24mp CMOS sensor that is 6 micron as well.

Only downside is less resolution but i don't think that would be that noticeable as you are still running a bit oversampled.

Binning 2x2 has smaller files, faster downloads and quicker to use for focusing, On CMOS though it does not result in much of an increased sensitivity like it does with CCD.

The QHY294m has a subpixel structure so 4 smaller subpixels are binned in its standard 11mp mode. It can be unlocked though to give the full 47mps at 1x1 binning and these are 2.3 microns. But binned you are getting 4.6 microns.

1x1 binning is harder on showing tilt and optical aberrations that would not normally be noticeable.

I have some images done at nearly 3 metres, QHY600m with 3.76 micron pixels and binned 2x2. They turned out fine.

2x2 binning increases the full well depth a lot as well so there is an advantage there in a scene with bright highlights.

Greg.
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Old 09-03-2021, 11:07 PM
DIYman (Doug)
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Many thanks Greg for your informative reply. It has been a great help. Clears skies, Doug
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