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06-08-2016, 04:32 PM   #1
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SMC Pentax 67 f/2.8 - Jagged aperture blades?

If anybody has this lens, please would you check if the aperture blades form a sawtooth or jagged pattern as you stop down from f/2.8 to f/8? At f/8, the aperture blades form a normal shape without jaggies.

From f/8 to f/22, one of the blades seems shorter than the others, giving a non-perfect 'circle' that is lopsided.

Thanks.

<EDIT> This is the 165mm f/2.8 </EDIT>


Last edited by glass; 06-09-2016 at 01:46 AM.
06-08-2016, 05:09 PM   #2
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QuoteOriginally posted by glass Quote
If anybody has this lens, please would you check if the aperture blades form a sawtooth or jagged pattern as you stop down from f/2.8 to f/8? At f/8, the aperture blades form a normal shape without jaggies.

From f/8 to f/22, one of the blades seems shorter than the others, giving a non-perfect 'circle' that is lopsided.

Thanks.
What lens exactly? You forgot the focal length

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06-08-2016, 05:10 PM   #3
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What / Which f2.8 lens are you referring to?
06-09-2016, 01:46 AM   #4
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Doh! 165mm f/2.8.

06-09-2016, 12:11 PM   #5
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yes, i notice that in my 165mm 2.8 lens.
06-09-2016, 12:46 PM   #6
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Mine too.
06-09-2016, 01:28 PM   #7
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Great, thanks. Wonder why they designed it like that? 10 aperture blades is an unusual number as well, I wonder if there is an optical reason for this.
06-09-2016, 03:04 PM   #8
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Many of the 6x7 lenses have diaphragms that have that jagged appearance when stopped down part way. It is a bad thing because it has more surface area from which to cause diffraction. The hole at smallest aperture should be round and centered. I have seen a few lenses where this was not the case.

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