Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-13-2014, 02:33 AM   #1
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
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
before rushing to judgement are you using the filters included with the lens?
11-13-2014, 06:33 AM   #3
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 43,114
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's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

11-13-2014, 10:13 AM   #4
Pentaxian




Join Date: Feb 2009
Location: Arizona
Posts: 911
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
Forum Member




Join Date: Jun 2014
Posts: 73
Original Poster
QuoteOriginally posted by Adam Quote
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?

QuoteOriginally posted by Digitalis Quote
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
Veteran Member
Thomasbrowphoto's Avatar

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
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
Pentaxian




Join Date: May 2011
Location: All over the place
Posts: 2,579
I don't have this issue with my 25 and the Z...

11-14-2014, 04:04 PM   #9
Senior Member




Join Date: Nov 2010
Location: Calgary, Alberta
Posts: 270
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
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
Senior Member




Join Date: Nov 2010
Location: Calgary, Alberta
Posts: 270
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
Veteran Member
Thomasbrowphoto's Avatar

Join Date: May 2014
Location: NSW, Australia
Posts: 335
QuoteOriginally posted by rob8888 Quote
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
Forum Member




Join Date: Jun 2014
Posts: 73
Original Poster
QuoteOriginally posted by Thomasbrowphoto Quote
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
Veteran Member
Thomasbrowphoto's Avatar

Join Date: May 2014
Location: NSW, Australia
Posts: 335
QuoteOriginally posted by rob8888 Quote
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
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.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
25mm, 25mm 645 lens, 25mm da645 exposure, 25mm f4 da, 645d, 645z, aperture, camera, da645, exposure, exposure variations, f4, lens test, medium format, range, row, test
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-3 exposure issues Romeo Bravo Troubleshooting and Beginner Help 3 07-27-2014 08:19 AM
Bounce flash over exposure issues solved in latest firmwares? Lage Pentax DSLR Discussion 11 10-22-2013 08:51 AM
Hello! I have a K-30 with exposure issues elijah Troubleshooting and Beginner Help 9 08-14-2013 07:07 AM
Fix the flash exposure issues Pentax! Lage Pentax DSLR Discussion 45 11-25-2012 08:02 AM
Où trouver l'objectif DA645 25MM F/4 ? vincen General Talk 3 06-10-2012 07:53 AM



All times are GMT -7. The time now is 09:28 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top