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04-04-2011, 11:01 AM   #1
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Pentax elements in groups

Does anyone happen to know wich Pentax lens produces less flare-halo in high contrast scenes theoretically: a 7 elements in 5 groups or a 6 elements in 6 groups one?
This question mainly adresses to wether we should count elements or groups to figure the reflecting surfaces on Pentax lenses.
Thanks in advance.

04-04-2011, 11:04 AM   #2
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Since SMC Pentax lenses have something like 99% light transmission because of the coatings, this should be pretty much moot for practical purposes.
04-04-2011, 12:48 PM   #3
arv
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There are quite interesting data on lenstip.com. They measured transmission of da 17 - 70 and fa 50mm, and found it quite similar (92 - 94%). But flare resistance was quite differrent (17 - 70 much worse). Thus number of groups (glass to air surfaces) might be more important then number of elements or transmission. But other factors might be also important, like curvature of surfaces, glass thickness, material, etc.
A.
04-05-2011, 08:28 AM   #4
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Hm, so glass to air surfaces come out from number of groups, not number of elements? Do the same stand for a kind of "fog" that covers the image when shooting against strong lights?

04-05-2011, 07:43 PM   #5
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Both flare and ghosting are caused by internal reflections. Refraction (and thus reflection) depends on difference of refractive indices of contacting medias, and as air is closer to vacuum than glass, glass to air surfaces should have more influence for reflections than glass to glass or glass to plastic surfaces (thats IMHO )
A.
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