Pixel size V Focal Length for same resolution (0.25")

[Pete Presland]

While "working" today thoughts always turn to all things astronomy.

I was thinking about, image scale of about 0.25 arc seconds/pixel for my white light imaging with the Evostar 120mm. Using my DMK21 I have to push the focal length up to 4500mm to achieve 0.25". With the ASI120mm its only 3000mm for 0.24".

I am guessing I should be using the ASI120 at least for white imaging?  Surely imaging at a much shorter FL but retaining the same resolution is going to be more forgiving to the conditions.

I do use the DMK21 for H/A, but that is due to the lack newton rings problem associated with the ASI.

[MarsG76]

Yeah, I agree.. a shorter FL will be less susceptible to the hardware and atmospheric conditions, so it would be beneficial.