DA645 25mm AL - please let me know your experience.

rob8888 · 05-13-2015, 07:15 PM

Recently had my (almost virgin) 25mmDA return from repair. The lens had a 2-3 stop exposure divergence from f4-f32 (becoming consistently more overexposed).

Just tested it again and it's still happening.

If you own this lens, could you please report your experience by setting your 645 (z or d) to manual.

Start at f4 (select relevant shutter) and take a frame. Then go up an aperture and down a shutter speed, all the way to f32. Then report how even yr exposures are throughout the range.

Thanks, Rob

Adam · 05-13-2015, 07:47 PM

When I tested the lens it was consistent, except the wider apertures were a bit darker due to vignetting, of course. Definitely no overexposure.

I've had it happen with a few K-mount lenses, though. Could be that the fault in the aperture mechanism wasn't actually repaired...

Thomasbrowphoto · 05-13-2015, 08:13 PM

Originally posted by rob8888

Recently had my (almost virgin) 25mmDA return from repair. The lens had a 2-3 stop exposure divergence from f4-f32 (becoming consistently more overexposed).

Just tested it again and it's still happening.

If you own this lens, could you please report your experience by setting your 645 (z or d) to manual.

Start at f4 (select relevant shutter) and take a frame. Then go up an aperture and down a shutter speed, all the way to f32. Then report how even yr exposures are throughout the range.

Thanks, Rob

Hi Rob,

Did they say exactly what they repaired? I have the lens also recently back from repair for Severe Barrel Movement , which was fixed but then returned with non working AF. Now I have it again and all is good. I haven't checked as finely as you for exposure variances with the lens, but from general shooting its all working okay. If I get a chance through the week ill have a look at it.

rob8888 · 05-14-2015, 06:09 AM

Hi Thomas. Yes, they said they replaced the PC board in it. Nothing about the aperture itself. Rob

algrove · 05-14-2015, 10:16 AM

Mine seems fine, however I have not done detailed analyses like you request.

rob8888 · 05-14-2015, 01:43 PM

I forgot to say that it takes about 1minute to do. Just flick through the images on the playback screen and you will immediately see the issue.

Also, just saying your lens seems fine without trying doesn't really help. I had no idea either until I tried it.

rob8888 · 05-17-2015, 12:42 PM

Disappointed I can't get anyone's help on this quick request - it's literally 1 minute of your time and would cast light onto a problem potentially affecting others.

Lacunapratum · 05-17-2015, 01:03 PM

I have two and none has an issue of that sort that you describe.

rob8888 · 05-17-2015, 01:04 PM

Thank you for trying it out.

Lacunapratum · 05-17-2015, 01:04 PM

One of mine has more play in the manual focus ring than I would like though.

mikeSF · 05-17-2015, 03:32 PM

i'll play. gimme a bit to go pull out gear and will get back to you

mikeSF · 05-17-2015, 04:50 PM

ok, i did the test (D FA version) and it maintains exposure with no detectable deviation except at f/4 which shows some vignetting.
I did the test your way...starting at f/4 and increasing shutter one stop for every aperture stop closed, up to f/22.
Then I started at f/8, established proper exposure then used AE-L and worked up and down the aperture settings...the camera also maintained proper exposure throughout.
Something is definitely wrong with your equipment.
good luck.

rob8888 · 05-18-2015, 12:15 AM

Thank you very much Mike, that's very kind of you. Yes, the vignetting wide open is real, but the exposure wander of several stops is not. I wonder what they did in Japan for 3 months? Not happy, I've only used it a few times since new. Thanks, Rob

mikeSF · 05-18-2015, 08:38 AM

Originally posted by rob8888

Thank you very much Mike, that's very kind of you. Yes, the vignetting wide open is real, but the exposure wander of several stops is not. I wonder what they did in Japan for 3 months? Not happy, I've only used it a few times since new. Thanks, Rob

you should ask for a warranty replacement.

rob8888 · 05-18-2015, 11:46 PM

Originally posted by mikeSF

you should ask for a warranty replacement.

Problem is they're a discontinued line now. The suggestion is a 28-45mm, but it's a major commitment for wilderness photography (which may involve 10 days or more lugging). That would push me back my old Canon kit which I don't want to do!

05-13-2015, 07:15 PM	#1
rob8888 Forum Member Join Date: Jun 2014 Posts: 73	DA645 25mm AL - please let me know your experience. Recently had my (almost virgin) 25mmDA return from repair. The lens had a 2-3 stop exposure divergence from f4-f32 (becoming consistently more overexposed). Just tested it again and it's still happening. If you own this lens, could you please report your experience by setting your 645 (z or d) to manual. Start at f4 (select relevant shutter) and take a frame. Then go up an aperture and down a shutter speed, all the way to f32. Then report how even yr exposures are throughout the range. Thanks, Rob

05-13-2015, 07:47 PM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	When I tested the lens it was consistent, except the wider apertures were a bit darker due to vignetting, of course. Definitely no overexposure. I've had it happen with a few K-mount lenses, though. Could be that the fault in the aperture mechanism wasn't actually repaired... Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

05-17-2015, 01:04 PM	#10
Lacunapratum Senior Member Join Date: Mar 2012 Posts: 164	One of mine has more play in the manual focus ring than I would like though. Last edited by Lacunapratum; 05-17-2015 at 05:49 PM.

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05-13-2015, 08:13 PM	#3
Thomasbrowphoto Veteran Member Join Date: May 2014 Location: NSW, Australia Posts: 335	Originally posted by rob8888 Recently had my (almost virgin) 25mmDA return from repair. The lens had a 2-3 stop exposure divergence from f4-f32 (becoming consistently more overexposed). Just tested it again and it's still happening. If you own this lens, could you please report your experience by setting your 645 (z or d) to manual. Start at f4 (select relevant shutter) and take a frame. Then go up an aperture and down a shutter speed, all the way to f32. Then report how even yr exposures are throughout the range. Thanks, Rob Hi Rob, Did they say exactly what they repaired? I have the lens also recently back from repair for Severe Barrel Movement , which was fixed but then returned with non working AF. Now I have it again and all is good. I haven't checked as finely as you for exposure variances with the lens, but from general shooting its all working okay. If I get a chance through the week ill have a look at it.

05-14-2015, 06:09 AM	#4
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Hi Thomas. Yes, they said they replaced the PC board in it. Nothing about the aperture itself. Rob

05-14-2015, 10:16 AM	#5
algrove Senior Member Join Date: Mar 2015 Posts: 160	Mine seems fine, however I have not done detailed analyses like you request.

05-14-2015, 01:43 PM	#6
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	I forgot to say that it takes about 1minute to do. Just flick through the images on the playback screen and you will immediately see the issue. Also, just saying your lens seems fine without trying doesn't really help. I had no idea either until I tried it.

05-17-2015, 12:42 PM	#7
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Disappointed I can't get anyone's help on this quick request - it's literally 1 minute of your time and would cast light onto a problem potentially affecting others.

05-17-2015, 01:03 PM	#8
Lacunapratum Senior Member Join Date: Mar 2012 Posts: 164	I have two and none has an issue of that sort that you describe.

05-17-2015, 03:32 PM	#11
mikeSF Pentaxian Join Date: Jan 2009 Location: East Bay Area, CA Photos: Gallery Posts: 6,620	i'll play. gimme a bit to go pull out gear and will get back to you

05-17-2015, 04:50 PM	#12
mikeSF Pentaxian Join Date: Jan 2009 Location: East Bay Area, CA Photos: Gallery Posts: 6,620	ok, i did the test (D FA version) and it maintains exposure with no detectable deviation except at f/4 which shows some vignetting. I did the test your way...starting at f/4 and increasing shutter one stop for every aperture stop closed, up to f/22. Then I started at f/8, established proper exposure then used AE-L and worked up and down the aperture settings...the camera also maintained proper exposure throughout. Something is definitely wrong with your equipment. good luck.

05-18-2015, 12:15 AM	#13
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Thank you very much Mike, that's very kind of you. Yes, the vignetting wide open is real, but the exposure wander of several stops is not. I wonder what they did in Japan for 3 months? Not happy, I've only used it a few times since new. Thanks, Rob

05-18-2015, 08:38 AM	#14
mikeSF Pentaxian Join Date: Jan 2009 Location: East Bay Area, CA Photos: Gallery Posts: 6,620	Originally posted by rob8888 Thank you very much Mike, that's very kind of you. Yes, the vignetting wide open is real, but the exposure wander of several stops is not. I wonder what they did in Japan for 3 months? Not happy, I've only used it a few times since new. Thanks, Rob you should ask for a warranty replacement.

05-18-2015, 11:46 PM	#15
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Originally posted by mikeSF you should ask for a warranty replacement. Problem is they're a discontinued line now. The suggestion is a 28-45mm, but it's a major commitment for wilderness photography (which may involve 10 days or more lugging). That would push me back my old Canon kit which I don't want to do!