I have an observing project that requires a 30 -- 40 cm (12 -- 16 inch) diameter primary and no refractive/transmissive elements (i.e. lenses).
Telescopes like this Ritchey–Chrétien has a back focus of 288mm from the rear cell. This is a typical value for the back focus for such instruments.
The problem I have is that the instrument I will be using on the telescope will foul the telescope mount if it is placed at this back focus distance.
I am looking for a purely reflective telescope where the back focus needs to be as close as possible to the rear cell.
Does anyone have any suggestions?
If I cannot find a suitable solution "off-the-shelf", I will have to look into refiguring the secondary mirror.