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rob8888 · 11-13-2014, 02:33 AM

Just did 2 exposure tests on a brand new 25mm DA645.

1) Ran through full aperture range, dropping -1 shutterspeed to +1 aperture increase. Difference between f4 and f32 is several stops?! (top row)
2) surprised, I then ran same through on Av, Increasing aperture and leaving camera to choose shutter (bottom row).

Not sure what to make of this yet, but test 2 is indicating the lens is not f4, but more like f4.5. And the non-linear relationship in test 1 concerns me - either the aperture values are way out, or the aperture itself is sticky?

Has anyone else struck this? What do you think? (FYI, I repeated with a 35mm 'A' and a 55mm D-FA and got very little variation across the aperture range).

Many thanks, Rob

**Digitalis** · 11-13-2014, 04:18 AM

before rushing to judgement are you using the filters included with the lens?

Adam · 11-13-2014, 06:33 AM

I think vignetting might be to blame. It's fairly pronounced wide-open.

desertscape · 11-13-2014, 10:13 AM

It's as if your metering system is reading your shutter speed but your diaphragm settings are not being read. An electrical connection?

rob8888 · 11-13-2014, 02:01 PM

Originally posted by Adam

I think vignetting might be to blame. It's fairly pronounced wide-open.

Hi Adam. It's way too pronounced for that and it's right across the frame. Haven't measured but it could be 2-3 stops off the centreline?

Originally posted by Digitalis

before rushing to judgement are you using the filters included with the lens?

Hi Digitalis. Yes, I had the factory clear/uv in. Ps, our digitalis is just coming into flower here. Shame it's a significant weed as it's a beautiful plant.

Rob

Thomasbrowphoto · 11-13-2014, 03:53 PM

This is very interesting. I had similar issues when I first got the DA25mm lens on my 645Z. But my encounter was a lot worse... and it turned out to be the aperture leaver getting jammed in the camera body. Not sure if its the same problem. I now have the same lens but on a new replacement body no problems so far... Just keep an eye on it. My differences were about 5-6 stops and inconsistent.

rob8888 · 11-13-2014, 04:10 PM

Thanks mate, that's interesting to know. Did it just happen with the 25mm or all lenses? I'm assuming all lenses if it was the body? I didn't see it with the 55DFA. Rob

itshimitis · 11-13-2014, 06:47 PM

I don't have this issue with my 25 and the Z...

Royce Howland · 11-14-2014, 04:04 PM

For what it's worth, I too have not seen anything like this with my 645D / 645Z and the DA 25mm. Some of those test results might be attributable to small metering variances. But the manual sequence in particular looks like the whole series was not exposing properly, after the first exposure. Possibly the aperture indeed is not getting stopped down properly beyond f/4. This would be easy enough to test using an extreme near/far composition focused on either the foreground or background, and shot at f/4 and then again at f/32. It could be double-checked in Live View with the DOF-preview button as well.

What version of firmware is on the 645Z? There were a number of bugs in the first firmware that shipped with the camera, that were fixed in the update put out a few weeks ago. If your Z isn't running the newest firmware, I highly recommend updating it right away. I found a number of the initial firmware bugs but most were merely annoyances that could be worked around, but still... Also, do you have any camera settings / custom functions enabled that could be monkeying with exposure? I normally disable all of these automagic functions, and shoot in full manual mode most of the time. As I said, I haven't seen a series like your series #1 come out of my D or Z.

When you repeated the test with the D-FA 55mm this should have indicated if there was a problem with the camera body (e.g. an aperture lever failure like Thomas experienced). The 55mm has a similar 100% camera-controlled aperture mechanism, lacking any physical aperture ring on the lens. Since the 55mm lens worked, all other things being equal, I'm suspecting a problem with your DA 25mm...

rob8888 · 11-14-2014, 06:15 PM

Hi Royce

Thanks for taking the time. Lots to think about. And yes, it is the latest firmware I've updated to.

Agree regarding the 55mm. It definitely seems like a lens thing.

I accept that there could be some exposure differences attributable to the Z 'monkeying' around with the exposure, and I also agree that vignetting has a role, but it's looking like a 2-3 stop deviation in the centre.

I'll try to find some time to do more tests in the next couple of days.

Thanks, Rob

Royce Howland · 11-14-2014, 07:06 PM

Yes, from the way your sample set looks it's a deviation of at least 2 - 3 stops and I can't think of a way to consider it "normal" unless the ambient light itself really was changing to that degree. Thinking about other things like firmware, automagic exposure settings and whatever is just a way to rule out the obvious. But my gut says there's something with your lens...

Thomasbrowphoto · 11-17-2014, 03:30 PM

Originally posted by rob8888

Thanks mate, that's interesting to know. Did it just happen with the 25mm or all lenses? I'm assuming all lenses if it was the body? I didn't see it with the 55DFA. Rob

Hi sorry on the late reply! Initially it was only with the DA25mm but then happened with any lens I tried to use. Could be a completely different issue though.

rob8888 · 12-17-2014, 10:12 PM

Originally posted by Thomasbrowphoto

Hi sorry on the late reply! Initially it was only with the DA25mm but then happened with any lens I tried to use. Could be a completely different issue though.

Interesting. Tried out my DA25mm lens on another new 645z and it did it on that camera also (has done it on all firmware versions too). About a 3 stop difference from wide open to closed aperture on the same Ev value through the range and it's only taken about 50 frames to date. Didn't happen with the 28-45. Hence it's gone back for checking.
Rob

Thomasbrowphoto · 03-31-2015, 10:12 PM

Originally posted by rob8888

Interesting. Tried out my DA25mm lens on another new 645z and it did it on that camera also (has done it on all firmware versions too). About a 3 stop difference from wide open to closed aperture on the same Ev value through the range and it's only taken about 50 frames to date. Didn't happen with the 28-45. Hence it's gone back for checking.
Rob

How did you go with the lens getting sent off mate, was it corrected or replaced? I hope it was a good outcome.

rob8888 · 03-31-2015, 10:14 PM

Hi there. Good timing. Just arrived back from Japan yesterday. PC board replaced. Haven't tried it yet.

11-13-2014, 06:33 AM	#3
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,608	I think vignetting might be to blame. It's fairly pronounced wide-open. 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:

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11-13-2014, 02:33 AM	#1
rob8888 Forum Member Join Date: Jun 2014 Posts: 73	25mm DA645 exposure issues? Just did 2 exposure tests on a brand new 25mm DA645. 1) Ran through full aperture range, dropping -1 shutterspeed to +1 aperture increase. Difference between f4 and f32 is several stops?! (top row) 2) surprised, I then ran same through on Av, Increasing aperture and leaving camera to choose shutter (bottom row). Not sure what to make of this yet, but test 2 is indicating the lens is not f4, but more like f4.5. And the non-linear relationship in test 1 concerns me - either the aperture values are way out, or the aperture itself is sticky? Has anyone else struck this? What do you think? (FYI, I repeated with a 35mm 'A' and a 55mm D-FA and got very little variation across the aperture range). Many thanks, Rob

11-13-2014, 04:18 AM	#2
Digitalis Site Supporter Join Date: Mar 2009 Location: Melbourne, Victoria Photos: Gallery Posts: 11,695	before rushing to judgement are you using the filters included with the lens?

11-13-2014, 10:13 AM	#4
desertscape Pentaxian Join Date: Feb 2009 Location: Arizona Posts: 1,272	It's as if your metering system is reading your shutter speed but your diaphragm settings are not being read. An electrical connection?

11-13-2014, 02:01 PM	#5
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Originally posted by Adam I think vignetting might be to blame. It's fairly pronounced wide-open. Hi Adam. It's way too pronounced for that and it's right across the frame. Haven't measured but it could be 2-3 stops off the centreline? Originally posted by Digitalis before rushing to judgement are you using the filters included with the lens? Hi Digitalis. Yes, I had the factory clear/uv in. Ps, our digitalis is just coming into flower here. Shame it's a significant weed as it's a beautiful plant. Rob

11-13-2014, 03:53 PM	#6
Thomasbrowphoto Veteran Member Join Date: May 2014 Location: NSW, Australia Posts: 335	This is very interesting. I had similar issues when I first got the DA25mm lens on my 645Z. But my encounter was a lot worse... and it turned out to be the aperture leaver getting jammed in the camera body. Not sure if its the same problem. I now have the same lens but on a new replacement body no problems so far... Just keep an eye on it. My differences were about 5-6 stops and inconsistent.

11-13-2014, 04:10 PM	#7
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Thanks mate, that's interesting to know. Did it just happen with the 25mm or all lenses? I'm assuming all lenses if it was the body? I didn't see it with the 55DFA. Rob

11-13-2014, 06:47 PM	#8
itshimitis Pentaxian Join Date: May 2011 Location: All over the place Posts: 3,535	I don't have this issue with my 25 and the Z...

11-14-2014, 04:04 PM	#9
Royce Howland Senior Member Join Date: Nov 2010 Location: Calgary, Alberta Posts: 275	For what it's worth, I too have not seen anything like this with my 645D / 645Z and the DA 25mm. Some of those test results might be attributable to small metering variances. But the manual sequence in particular looks like the whole series was not exposing properly, after the first exposure. Possibly the aperture indeed is not getting stopped down properly beyond f/4. This would be easy enough to test using an extreme near/far composition focused on either the foreground or background, and shot at f/4 and then again at f/32. It could be double-checked in Live View with the DOF-preview button as well. What version of firmware is on the 645Z? There were a number of bugs in the first firmware that shipped with the camera, that were fixed in the update put out a few weeks ago. If your Z isn't running the newest firmware, I highly recommend updating it right away. I found a number of the initial firmware bugs but most were merely annoyances that could be worked around, but still... Also, do you have any camera settings / custom functions enabled that could be monkeying with exposure? I normally disable all of these automagic functions, and shoot in full manual mode most of the time. As I said, I haven't seen a series like your series #1 come out of my D or Z. When you repeated the test with the D-FA 55mm this should have indicated if there was a problem with the camera body (e.g. an aperture lever failure like Thomas experienced). The 55mm has a similar 100% camera-controlled aperture mechanism, lacking any physical aperture ring on the lens. Since the 55mm lens worked, all other things being equal, I'm suspecting a problem with your DA 25mm...

11-14-2014, 06:15 PM	#10
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Hi Royce Thanks for taking the time. Lots to think about. And yes, it is the latest firmware I've updated to. Agree regarding the 55mm. It definitely seems like a lens thing. I accept that there could be some exposure differences attributable to the Z 'monkeying' around with the exposure, and I also agree that vignetting has a role, but it's looking like a 2-3 stop deviation in the centre. I'll try to find some time to do more tests in the next couple of days. Thanks, Rob

11-14-2014, 07:06 PM	#11
Royce Howland Senior Member Join Date: Nov 2010 Location: Calgary, Alberta Posts: 275	Yes, from the way your sample set looks it's a deviation of at least 2 - 3 stops and I can't think of a way to consider it "normal" unless the ambient light itself really was changing to that degree. Thinking about other things like firmware, automagic exposure settings and whatever is just a way to rule out the obvious. But my gut says there's something with your lens...

11-17-2014, 03:30 PM	#12
Thomasbrowphoto Veteran Member Join Date: May 2014 Location: NSW, Australia Posts: 335	Originally posted by rob8888 Thanks mate, that's interesting to know. Did it just happen with the 25mm or all lenses? I'm assuming all lenses if it was the body? I didn't see it with the 55DFA. Rob Hi sorry on the late reply! Initially it was only with the DA25mm but then happened with any lens I tried to use. Could be a completely different issue though.

12-17-2014, 10:12 PM	#13
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Originally posted by Thomasbrowphoto Hi sorry on the late reply! Initially it was only with the DA25mm but then happened with any lens I tried to use. Could be a completely different issue though. Interesting. Tried out my DA25mm lens on another new 645z and it did it on that camera also (has done it on all firmware versions too). About a 3 stop difference from wide open to closed aperture on the same Ev value through the range and it's only taken about 50 frames to date. Didn't happen with the 28-45. Hence it's gone back for checking. Rob

03-31-2015, 10:12 PM	#14
Thomasbrowphoto Veteran Member Join Date: May 2014 Location: NSW, Australia Posts: 335	Originally posted by rob8888 Interesting. Tried out my DA25mm lens on another new 645z and it did it on that camera also (has done it on all firmware versions too). About a 3 stop difference from wide open to closed aperture on the same Ev value through the range and it's only taken about 50 frames to date. Didn't happen with the 28-45. Hence it's gone back for checking. Rob How did you go with the lens getting sent off mate, was it corrected or replaced? I hope it was a good outcome.

03-31-2015, 10:14 PM	#15
rob8888 Forum Member Join Date: Jun 2014 Posts: 73 Original Poster	Hi there. Good timing. Just arrived back from Japan yesterday. PC board replaced. Haven't tried it yet.

25mm DA645 exposure issues?

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