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Shouldn't the secondary mirror be of equal or better quality than the primary?

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  • "Mr. Wizard!"
    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
    Message 1 of 1 , Apr 10 5:14 AM
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      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.

      Thanks

      Art
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