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09-15-2008, 12:54 AM   #1
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A Question for DA 17-70/4 lens owners/users

Hi All,

Got chance to test out a DA1770 lens over the weekend. Seems the lens has some strange exposure behavior, especially at the tele end. The exposure is quite different from F4 to F8. At F4 it's a bit under exposed, while at F8 it's quite a bit over exposed. I used matrix metering.

70mm F4:


70mm F5.6:


70mm F8:


I wonder if all DA1770 lenses are like this, or the one I got is a lemon

09-15-2008, 02:00 AM   #2
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Huh. I've had that problem with variable-aperture zooms, but not constant-aperture ones. Do you have an aftermarket split prism focusing screen or anything? That was my problem.
09-15-2008, 02:09 AM   #3
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frank, I didn't know you played with dolls! Just joking, bro.

A little underexposure at max aperture I can understand (light fall off) but progressive increase in exposure as you stop down is a little baffling. Perhaps a test outdoors might yield different results.
09-15-2008, 07:44 AM   #4
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maybe the blades are not opening and closing correctly?

09-15-2008, 10:13 PM   #5
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QuoteOriginally posted by Finn Quote
Huh. I've had that problem with variable-aperture zooms, but not constant-aperture ones. Do you have an aftermarket split prism focusing screen or anything? That was my problem.
No, I'm using the original focusing screen came w/ the camera
09-15-2008, 10:15 PM   #6
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QuoteOriginally posted by creampuff Quote
frank, I didn't know you played with dolls! Just joking, bro.

A little underexposure at max aperture I can understand (light fall off) but progressive increase in exposure as you stop down is a little baffling. Perhaps a test outdoors might yield different results.
Yeah, thought I'd give it a try and see how it compare against the Sigma one. I hope the problem is w/ this copy only ...
09-15-2008, 10:16 PM   #7
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QuoteOriginally posted by k100d Quote
maybe the blades are not opening and closing correctly?
That I'm not really sure. I checked the exposure at 17mm and 36mm, also slight exposure difference, but not as bad as it is at 70mm end.
09-15-2008, 10:21 PM   #8
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I also checked the Sigma DC 17-70 lens, seems it also has some exposure problem at various aperture setting, but not as bad as the Pentax one.

Sigma DC 1770 @ 70mm F4.5:


Sigma DC 1770 @ 70mm F5.6:


Sigma DC 1770 @ 70mm F8:


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