Is there a minimum focal ratio needed to guide with in relation to your imaging scope? If you are using main scope at prime focus and both guider and imager are F5, does a 90degree diagonal increase focal length, or should you go to a 2x Barlow, does this make the field too small to find a guide star?
Can this be calculated, can /does someone know the formula/formulae and can they help me with the calculations or give me good examples to follow(I'm not very smart, but I can lift heavy things
)?
Thanks!