Quote:
Originally Posted by RussellH
Thanks guys.
This may be my lack of understanding, but I don’t know why they just don’t build them all with more back focus these days
|
Hi Russell,
It isn't a problem with some telescope designs, but it is with newtonians. The more back focus you have, the larger the secondary mirror required to fully illuminate the required field size. For visual astronomy you want to minimise the size of the secondary mirror, as a larger secondary mirror causes slight degradation in image quality. For astrophotography the size of the secondary mirror does not matter.
Cheers,
John B