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25450Re: [tec-scopes] Re: Minimum Strehl?

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  • Bruce MacEvoy
    Jul 3 1:52 PM
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      that's certainly true, alan ... but i think D&G makes anything higher than an ƒ/12 only as a custom job, with at least a two year wait time, and istar apparently only offers above ƒ/10 as lens cells, so you have to build your own baffled tube and focuser. the first question about long achromats is: where would you buy one? the remaining issues are ease of transporting it and structure costs to mount and house it. all that implies a very small user group at the outset -- hardly the basis for any conclusion about the optical merits.

      i'm not an achromat partisan -- i've tried them, enjoyed them, don't own one. my focus is on how arguments for optical quality are justified, why strehl is absolutely not a sufficient test for imaging quality, and why "seeing is believing" is, as a test of visual quality, often better than "theory says".

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