[04Stefan07 (Stefan)]

Originally Posted by Shiraz

depends entirely on the pixel size of the camera and the F Number of the scope.

easy rule of thumb is that the final F Number you obtain should be roughly equal to the camera pixel size in microns multiplied by 5.

For example if you have a camera with 3 micron pixels, you want around f15 - so if you have for example an f8 scope, you will get close to f15 with a 2x Barlow or if you have an f5 scope, 3x would be best. I have an f5 scope and 5.6 micron pixels, so I need about f28 and use a 5x Barlow.

this method optimises things for both the scope aperture and focal length - you only need to consider the pixel size and final f number and everything else falls into place.

Yep thank you!