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Old 05-07-2018, 06:47 AM
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Slawomir (Suavi)
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Join Date: Sep 2014
Location: North Queensland
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Quote:
Originally Posted by Hans Tucker View Post
The Takahashi FS series refractors seem to produce good results.
A very good doublet at a slowish (for imaging) focal ratio will produce good results. However, a very good triplet will yield photographically better result at the same focal ratio.

Blue end of the spectrum usually suffers in a doublet. Attached is a neat chart from Takahashi comparing chromatic correction of a triplet and a doublet both with the same aperture and focal ratios.


@Greg - unless there are reasons not to go with CFF, I think their limited edition 135mm f/6.7 triplet with 3.5FTF might be just the right scope for both visual and imaging (it has a large dedicated corrector resulting in a 55mm corrected imaging circle).
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