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04-23-2009, 02:50 PM   #1
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Faulty DA* 16-50mm ??

I am afraid that I might have submitted two entries for the same topic but I can't seem to find the one I previously submitted. Adam, please help delete if it is.

I have a problem with this lens and could use some help to validate if this is a faulty copy of the DA* 16-50mm. Aside from getting sharp pictures I am not getting the lens to keep the exposure value when I use Av mode and just changing aperture here is what I mean.

I have taken following 3 sample shots. Two with the DA* 16-50mm and one with the DA* 50-135mm (which I think is good) to compare.

All 3 shots are taken with the K10D at FL 50mm, ISO 320, center focus and Av mode.
1) DA* 16-50mm f5.6 1/320
2) DA* 16-50mm f2.8 1/1000
3) DA* 50-135mm f2.8 1/1000

Please let me know if I have a faulty copy of this lens. Appreciate all your help.


Last edited by aleonx3; 10-08-2010 at 11:02 AM.
04-23-2009, 05:42 PM   #2
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Does your aperture blades close correctly? does it move freely?

Check the shots in M mode... set aperture to the same values and change the aperture... does the picture in f2.8 look brighter than f5.6? if it works correctly it will and the problem may be a contact/camera issue reading the correct values. If it doesn't change it may be a problem with the lense...

Cheers
Shang
04-23-2009, 10:37 PM   #3
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Shang looks to be onto something; it does look like the lens is staying open on the 16-50 even when it was stopped down to 5.6 on the K10d. I can see you used the same form of metering (multi-segment) for all three shots. Also, all 3 shots were taken within a few minutes of each other, so lighting changes are not likely the cause either. No ev compensation used in any of the shots.

And the 2.8 exposure for the 16-50 clearly compares like it should to the 50-135. The overexposed image, 1st one, is the odd ball out. I do not own the Da 16-50mm--can it be manually stopped down? Does the 50-135 appear to stop down on the K10d?
04-23-2009, 11:56 PM   #4
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QuoteOriginally posted by aleonx3 Quote
I am afraid that I might have submitted two entries for the same topic but I can't seem to find the one I previously submitted. Adam, please help delete if it is.


No you hadn't submitted this twice. If you want to find threads you have started or posts you have made, look on your profile page unders 'statistics'.

If you want to contact an administrator or moderator (moderators should be your first port of call), PM one of them. Hiding a message within a post isn't going to get a response unless we stumble upon it by accident as I have just done.

04-24-2009, 08:49 AM   #5
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QuoteOriginally posted by sychen Quote
Does your aperture blades close correctly? does it move freely?

Check the shots in M mode... set aperture to the same values and change the aperture... does the picture in f2.8 look brighter than f5.6? if it works correctly it will and the problem may be a contact/camera issue reading the correct values. If it doesn't change it may be a problem with the lense...

Cheers
Shang
Thanks, Shang, I should have tested it before I took it to Pentax Canada repair this morning. I will find out from them if it is just the contact. I forgot to include anothe image I took with the DA* 50-135mm stopping down to f5.6 1/320. Here it is (quite different from the DA* 16-50mm)

See below the image.
4) DA* 50-135mm f5.6 1/320 iso320

QuoteOriginally posted by Jewelltrail Quote
Shang looks to be onto something; it does look like the lens is staying open on the 16-50 even when it was stopped down to 5.6 on the K10d. I can see you used the same form of metering (multi-segment) for all three shots. Also, all 3 shots were taken within a few minutes of each other, so lighting changes are not likely the cause either. No ev compensation used in any of the shots.

And the 2.8 exposure for the 16-50 clearly compares like it should to the 50-135. The overexposed image, 1st one, is the odd ball out. I do not own the Da 16-50mm--can it be manually stopped down? Does the 50-135 appear to stop down on the K10d?
Thanks, Jewelltrail, I think the over-exposure problem rather obvious, but the images are also soft (though I am not using good examples here). I also tried other shots, CA is quite pronounced in high contrast areas. OTOH, I don't believe that there is a BF/FF issue although I am not so sure. My DA* 50-135mm works perfectly fine on my K10D. I am hoping that Pentax Canada repair shop can give me a correct assessment.

QuoteOriginally posted by Damn Brit Quote
No you hadn't submitted this twice. If you want to find threads you have started or posts you have made, look on your profile page unders 'statistics'.

If you want to contact an administrator or moderator (moderators should be your first port of call), PM one of them. Hiding a message within a post isn't going to get a response unless we stumble upon it by accident as I have just done.
Gary, thanks for your great advice, I will make sure I do that in the future.

I want to thank you all for helping me out. I am troubled by how this is handled by Pentax US repair center. In the meantime, I want to give them a chance to sort this out and I just want to get this lens to work properly.

Last edited by aleonx3; 10-08-2010 at 11:02 AM.
04-24-2009, 09:21 AM   #6
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I see you already sent the lens for service, which was the right solution as there seems to be something wrong... One thing that can cause this is an aperture diaphragm which sticks open, not stopping down the aperture when the shot is taken. My Tamron 70-200 started doing this and it's in for warranty work right now - Tamron has confirmed that they're replacing the aperture mechanism.
04-24-2009, 09:45 AM   #7
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QuoteOriginally posted by heliphoto Quote
I see you already sent the lens for service, which was the right solution as there seems to be something wrong... One thing that can cause this is an aperture diaphragm which sticks open, not stopping down the aperture when the shot is taken. My Tamron 70-200 started doing this and it's in for warranty work right now - Tamron has confirmed that they're replacing the aperture mechanism.
Josh, thanks for your response.

What you have just described make sense to me. Without the aperture ring on the lens, it is difficult to see if the diaphragm gets stuck or not (can only change on the camera). So, even if I stopped down the aperture in the camera, the diaphragm remains wide open. Could this be caused by faulty contact as well?
Anyway, I am waiting for Pentax Canada repair shop to provide the verdict.

Thanks, Alfred
04-24-2009, 10:14 AM   #8
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Well, I don't really know how the electronics work with the lens so I can't answer that question. A way to see if the aperture is getting stuck is set the camera to M with something like f/22 and a 1 sec. exposure, and then to look into the lens and watch the diaphragm do it's thing. It'll be quite obvious if it stops down or not.

04-24-2009, 11:57 AM   #9
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QuoteOriginally posted by heliphoto Quote
Well, I don't really know how the electronics work with the lens so I can't answer that question. A way to see if the aperture is getting stuck is set the camera to M with something like f/22 and a 1 sec. exposure, and then to look into the lens and watch the diaphragm do it's thing. It'll be quite obvious if it stops down or not.
Josh, thanks for the tips, I will try that again and hopefully learn a few more things.

Alfred
05-07-2009, 04:50 PM   #10
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Have you updated your firmware. Just a thought. Here is what I pulled off Pentax site. 1.3 helps with SDM lenses. Just a thought.

PENTAX K10D FIRMWARE UPDATE VERSION 1.30



VERSION HISTORY



Version 1.30

* Added compatibility with the supersonic motor drive of Pentax SDM lenses.

Version 1.20

* Added the required programming for compatability with the Pentax Remote Assistant 3 software.

Version 1.11

* Improved multiple exposure function when shooting in RAW.
* Corrected an issue with luminescence control and trailing shutter curtain sync when using the built-in flash.
05-07-2009, 05:19 PM   #11
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Interesting. Almost like the way a K or an M lens behaves on K10/K20.

Jer
05-07-2009, 06:03 PM   #12
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It has been almost 2 weeks since I took the 16-50mm lens and the K10D to Pentax Canada support. What I have been told is that there is something wrong with my K10D (a surprise to me). My other DA* 50-135mm lens does not have the same problem (go figure).

Thanks to all for your comments and suggestions. I will provide an update once I get the lens and camera back from Pentax Canada. I am still puzzled.
05-11-2009, 03:21 PM   #13
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Just received a replacement lens from Pentax Canada customer service today. It turns out that this is another replacement copy of the same lens I received from Pentax US (purchased from kuau).

I will do more testing on this lens and provide samples when I get a chance.

Thanks to everyone on this forum for their valuable input and suggestions.
Alfred
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