A Question for DA 17-70/4 lens owners/users

frank · 09-15-2008, 12:54 AM

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

Finn · 09-15-2008, 02:00 AM

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.

creampuff · 09-15-2008, 02:09 AM

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.

k100d · 09-15-2008, 07:44 AM

maybe the blades are not opening and closing correctly?

frank · 09-15-2008, 10:13 PM

Originally posted by Finn

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

frank · 09-15-2008, 10:15 PM

Originally posted by creampuff

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 ...

frank · 09-15-2008, 10:16 PM

Originally posted by k100d

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.

frank · 09-15-2008, 10:21 PM

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:

09-15-2008, 12:54 AM	#1
frank Veteran Member Join Date: Nov 2006 Location: Singapore Photos: Gallery Posts: 3,202	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

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09-15-2008, 02:00 AM	#2
Finn Veteran Member Join Date: Feb 2007 Location: Phoenix Photos: Gallery Posts: 1,056	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
creampuff Veteran Member Join Date: May 2007 Location: Singapore Photos: Gallery Posts: 3,953	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
k100d Veteran Member Join Date: Feb 2008 Location: Toronto Posts: 3,911	maybe the blades are not opening and closing correctly?

09-15-2008, 10:13 PM	#5
frank Veteran Member Join Date: Nov 2006 Location: Singapore Photos: Gallery Posts: 3,202 Original Poster	Originally posted by Finn 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
frank Veteran Member Join Date: Nov 2006 Location: Singapore Photos: Gallery Posts: 3,202 Original Poster	Originally posted by creampuff 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
frank Veteran Member Join Date: Nov 2006 Location: Singapore Photos: Gallery Posts: 3,202 Original Poster	Originally posted by k100d 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
frank Veteran Member Join Date: Nov 2006 Location: Singapore Photos: Gallery Posts: 3,202 Original Poster	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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