Shouldn't the secondary mirror be of equal or better quality than the primary?
- I've been checking Opto Sigma's offerings in small aluminized mirrors so I can spec out the 6" F-8 CHIEF.
They offer mirrors with various degrees of flatness: 1/4, 1/10 and 1/20 wave precision. Surplus Shed also offers some viable alternatives.
Which to choose?
I've puzzled over this issue of secondary mirror quality ever since I got hooked on designing and building OTA's
I figure that you get what you pay for. However, I don't expect to see the difference between 1/10 and 1/20 wave nor do I expect others with much younger eyes to do so either. However, at the other end of logic is the fact that all the resolving power of a large primary IS being concentrated on that small secondary. It's kind-a-like film photography: if you expect to make 30x enlargements from a small negative, it had best be fine grain film if you expect it to capture detail.
I view the resolving power of a secondary mirror in much the same way. Others, however, argue that high precision secondary's do not make enough of a difference to justify the extra expense.
I'll likely spring for the 1/10th wave flat simply because of budgetary constraints. I'd still enjoy seeing some other opinions.