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I don’t know if your after the image scale calculation of your image train but here is mine based on my 8” f5 newt and Canon DSLR
Image Scale or Pixel Scale Calculation - Over Sampling and Under Sampling
P is Image scale in arc sec/pixel
Formula
P= ( pixel size in microns x 206.3 )/ focal length in mm
Main Imaging Scope
New 8” f5 Newtonian imaging telescope (focal length is 1000mm)
Canon 600D pixel size is 4.3 microns
Therefore image scale would be 4.3 x 206.3 / 1000 = 0.88 arc sec/pixel
Over sampling is < 1.0 arc sec / pixel
Under sampling is > 2.0 arc sec / pixel
In good seeing conditions 0.80 to 1.0 arc sec/ pixel is OK stars will be round and sharp
In average to poor seeing conditions 0.80 to 1.0 arc sec/ pixel will produce slightly fuzzy or bloated stars
DSLR’s are generally only useful in telescopes with focal lengths less than 1200mm or > 0.80 arc sec per pixel
Guide Scope
Orion 50mm Guide scope ( focal length 162mm)
ZWO ASI120MM-3 Guide camera pixel size is 3.75 microns
Therefore image scale would be 3.75 x 206.3 / 162 = 4.77 arc sec/pixel
Image ratio imaging camera to guide camera
4.77 / 0.88 = 5.4 x
Guiding Advice
Advice is you should be below 4x image scale from guide scope camera to main imaging camera to guide at an acceptable error
Hope this is of some relevance to your question?
Cheers
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