[Startrek (Martin)]

I’ve read a lot of information on forums etc... which recommend your image scale should be less than 4x between your main imaging system and your guiding system optics to ensure acceptable guiding

I’ve calculated my system below -

Image Scale Calculation

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

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

Please let me know if I’ve made a mistake in the calculations or the methodology but my image scale differential is 5.4 x and I can comfortably guide at around 1 arc sec error , a little worse when seeing is ordinary and a little better sometimes

I welcome any comments from experienced IIS members in regard to the above

Thanks