Parabolic mirror for photography

[dannat]

For those who have short focal length Newts.. is a parabolic mirror an essential or is a spherical in which aberrations have been minimised ok for short exposure astrophotogrphy:shrug: Talking 5-6" ota

[dannat]

the weight is also a factor as the 5" is 3.5kg, as opposed to just over 5kg for the 6"

[Geoff45]

For a 6" you need about f9 for a spherical mirror to be acceptable, as long as you're not too picky. With a 5", you wouldn't go shorter than f8.
Geoff