Hi,
a question to the optical-formula gurus. Pentax describes the optics of
this mirror lens as 6 elements in 4 groups. Looking at the diagram that
they provide us, I see 8 elements. I will number them 1 through 8 when
looking from left to right. 1 and 2 as well as 5 and 6 seem to be forming
the two two-element groups (like the optical formula suggests), but what
about the rest?
I am thinking like this:
- elements 2 and 3 must be mirrors, so they might not be counted towards
the number of optical elements. Now we are down to 6 elements which
agrees with Pentax. But the number of groups is now 5.
- alternatively, element 8 is the screw-on filter, so that might not be
counted. Then we are left with 7-5. Still doesn's fit.
Your ideas are welcome. Cheers,
Boz
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