Chinese 115mm f/6.95 Triplet

Just wondering if the optical gurus (paging Rolando! )
could offer some insight/opinions/commentary about the info shown here--
http://astro.uni-tuebingen.de/~grzy/APO115auswertungneu.jpg

Specifically, the range of focus between C and F (70 microns).
e= 0
F= -50
C= +20 (microns)

How good an APO are we looking at, here? :S

>>Just wondering if the optical gurus (paging Rolando! )
could offer some insight/opinions/commentary about the info shown here--
http://astro.uni-tuebingen.de/~grzy/APO115auswertungneu.jpg >>

Well for one thing, the interferometer results are misleading because the spherical has been removed from the final figures.

The fringes show a lens with a large amount of spherical aberration, so the Strehl ratio would be much much lower than 0.97. For some reason they chose to remove the spherical component, so that leaves only the coma and astigmatism, which together contribute 0.16 wave or 1/6 wave P-V. That's quite high in my opinion, as these two should be much less than 1/10 wave total. The lens has a definite undercorrection of almost 1 fringe P-V which translates to 1/2 to maybe 1/3 wave P-V wavefront (I would have to analyze the fringes to get an exact figure).

So I would say, it's not well corrected for the fundamentals, never mind color correction. What good is perfect color correction if the image is fuzzy?

Rolando

Here is what a 130mmF6 triplet apo looks like when the elements are first assembled after grinding, edging and polishing, but before hand figuring and careful optical alignment.

Rolando

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