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What pixel size for F25

ZWO ASI533MC Planetary Camera CMOS Acquisition Solar System
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Andres Salaverria avatar
Andres Salaverria avatar
I image with a C8 at F25. This is at the limit of how much detail I can get with the ASI462 w/2.9um. I thought if I went with a bigger pixel size, I might get more detail, and I tried the ASI533MC with 3.76 microns. Oddly enough, in my little experiment the image I took with the 533 seemed a bit softer than the one I took with the 462. I was expecting the opposite result. Any opinions to share?

I am sure there are many other factors to consider, but at the moment I am interested in choosing between these two cameras (believing in using what you have). 

Thanks!
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Oscar Echeverri avatar
Oscar Echeverri avatar
I like to use this utility as a guideline as to the suitability of a given camera's pixel size to the telescope I want to image with: https://astronomy.tools/calculators/ccd_suitability

It's not a be-all-end-all to the discussion, but a good starting point.

The 533MC-Pro on an 8" @F25 will give you an image scale of 0.15"/pixel.  That's going to be all kinds of sensitive to even the most minute of guiding errors. And yes, in theory the it should be a more suitable image scale than that provided by the asi462, but not by much as the pixel scale there is 0.12"/px.
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Andres Salaverria avatar
Andres Salaverria avatar
Oscar Echeverri:
I like to use this utility as a guideline as to the suitability of a given camera's pixel size to the telescope I want to image with: https://astronomy.tools/calculators/ccd_suitability

It's not a be-all-end-all to the discussion, but a good starting point.

Thanks Oscar. I do use the tool, and I did some reading. I am looking for additional insight on this topic. Thank you!
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Oscar Echeverri avatar
Oscar Echeverri avatar
Andres Salaverria:
Oscar Echeverri:
I like to use this utility as a guideline as to the suitability of a given camera's pixel size to the telescope I want to image with: https://astronomy.tools/calculators/ccd_suitability

It's not a be-all-end-all to the discussion, but a good starting point.

Thanks Oscar. I do use the tool, and I did some reading. I am looking for additional insight on this topic. Thank you!

Right -- the asi533 will provide a more forgiving image scale to the asi462 for your set up.  As to why the images were softer in your comparison, could it have been that seeing was worse the night you used the 533?
andrea tasselli avatar
andrea tasselli avatar
The details you can record with either cameras have very little relation to pixel pitch. It would depend on external factors such as seeing and object altitude and internal factor such as collimation and what kind of barlow lens you're using. As all but telecentric focal extenders would give you variable focal multiplier as function of the sensor to barlow distance it is easy to adjust either to have the same pixel scale. With a C8 I wouldn't go beyond 5 meters at most.
Wouter D'hoye avatar
Wouter D'hoye avatar
Hi,

@ f/25 regardless of telescope size you will get optimal sampling with a camera having 5micron pixels. Bigger pixel size will result in undersampling, so less detail will be resolved. Smaller will oversample, resulting in a bigger image scale, but no extra detail resolved. Resolution of an optical system is determined by the opening (provided all other parts of the optical train are of good quality) Now, the guideline is f/ratio = 5 x pixelsize. if you on average have rather bad seeing conditions I’d recommend a slightly undersampled system. There is only little advantage to oversample, as the image will just ook dull and soft.

I use f/20 with 5,6 micron pixels. results are just fine.

now you can’t easily compare two imaging sessions. For high res imaging the seeing has most influence. 

cs

Wouter.
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