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Guidescope Focal Length
Appreciate some advice on an appropriate guide scope focal length for my Newtonian reflector with 900mm focal length as the more you read books and forums the more subjective it becomes
Using the following universal formula -
Resolution = 206 x pixel size / FL
My Main Scope
Where my DSLR camera has a pixel size of 4.29 um
Main scope focal length 900mm
Main scope resolution = 0.98 arcsec/pixel
Suggested Guide scope Orion 50mm mini with a ZWO ASI120MM-S
Orion 50mm mini has 162mm focal length
ZWO camera pixel size 3.75um
Suggested guide scope resolution = 4.77 arcsec/ pixel
Therefore the pixel difference being around 4 arcsec/ pixel
Reading various AP articles the difference between main scope and guide scope should be around 2 pixels to minimise error
Therefore based on above I should be using a guide scope with focal length between 300 to 400mm to achieve a 2 pixel differential ???
And yet the Orion 50mm mini states it can be used on main scopes up to 1500mm focal length
Am I reading it all wrong ??
I welcome any advice on the subject
Thanks in advance
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