Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-14-2015, 07:09 AM   #1
Site Supporter
Sluggo's Avatar

Join Date: Sep 2006
Location: Ames, Iowa
Photos: Gallery | Albums
Posts: 597
Pair of K20D bodies, having trouble matching exposure settings

For a while I've been using a pair of K20D bodies for 3D photography ("crossview"- type example here).

Generally I shoot in manual mode with a pair of identical lenses, and while I've been getting satisfactory results, I'm a little frustrated with exposures not matching even when shots are made simultaneously with matched ISO, aperture and shutter speed. One camera consistently exposes about one stop lower than the other, so I have to adjust for that while processing.

The "expanded dynamic range" option is switched off on both cameras, so it's not that -- even though it would have been a tidy explanation for true ISO being off by a stop. The cameras are both on firmware version 1.04. What else could account for the difference?

Is it possible the cameras just aren't that identical, because of different production runs or something?

06-14-2015, 07:37 AM   #2
Moderator PEG Judges
Kerrowdown's Avatar

Join Date: Aug 2008
Location: Highlands of Scotland.
Photos: Gallery
Posts: 32,563
I guess there could be some small differences in production, but a stop seems like a lot.

If you exposure compensate by one stop on the guilty one, will that save you in PP?
06-14-2015, 07:41 AM   #3
Site Supporter




Join Date: Jan 2011
Posts: 2,364
slower aperture in one of the lenses?
06-14-2015, 07:45 AM   #4
Pentaxian
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 4,238
Is exposure compensation zeroed on both bodies? Did you try resetting both to factory defaults and then putting back your customizations?

Did you try swapping lenses?

If the exposure difference is consistent why not set exposure compensation on one of the bodies if nothing else works.

06-14-2015, 08:31 AM   #5
Site Supporter
Sluggo's Avatar

Join Date: Sep 2006
Location: Ames, Iowa
Photos: Gallery | Albums
Posts: 597
Original Poster
I hadn't given the lenses much thought. No reason to assume that identical-model lenses should be more identical than the bodies are. Will experiment more and post again.

Edit: Sure enough, the lenses are different. But it's not that one of them has a slower iris - they are just calibrated to stop down differently. I can set F5.6 on the aperture rings of both and visually verify that the apertures aren't nearly the same size. But stop the larger one down to F8.0 and the openings about match. I believe that's the one that is calibrated too fast, rather than the first being too slow.

These are old Vivitar 19mm F3.8 manual focus cheapies. Sharp enough for what I'm doing, and a desirable length, but I guess it's no big surprise that the aperture settings aren't very precise. At least now I know which correction to make: I should run the lenses at different apparent apertures, not change the sensitivity on one of the camera bodies.

Last edited by Sluggo; 06-14-2015 at 02:05 PM. Reason: more info
06-14-2015, 02:19 PM   #6
Site Supporter




Join Date: Jan 2011
Posts: 2,364
glad to hear you solved the mistery
06-14-2015, 05:13 PM   #7
dms
Site Supporter




Join Date: Aug 2011
Location: New York, NY
Photos: Gallery
Posts: 1,620
I have the vivitar 21mm f/3.8 (T4) lens and I find (my copy) is about 2/3-1 stop slower than indicated at f/5.6.
06-14-2015, 06:31 PM   #8
Site Supporter
Sluggo's Avatar

Join Date: Sep 2006
Location: Ames, Iowa
Photos: Gallery | Albums
Posts: 597
Original Poster
QuoteOriginally posted by dms Quote
I have the vivitar 21mm f/3.8 (T4) lens and I find (my copy) is about 2/3-1 stop slower than indicated at f/5.6.
That's interesting. And "Vivitar" is/was just a marketing entity that never really manufactured any lenses, right? I wonder if their various suppliers have bent specifications in different ways or had varying quality control.

Even though my two 19mm lenses are the same model, they might have come from different manufacturers and have little in common other than similar-looking cases and the same published specs. Maybe one is really a Cosina inside and the other a Tokina or whatever.

06-14-2015, 06:44 PM   #9
Pentaxian
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 4,238
QuoteOriginally posted by Sluggo Quote
Even though my two 19mm lenses are the same model, they might have come from different manufacturers and have little in common other than similar-looking cases and the same published specs. Maybe one is really a Cosina inside and the other a Tokina or whatever.
Vivitar indicated the manufacturer with the first two digits of the serial numbers:

https://www.cameraquest.com/VivLensManuf.htm
06-14-2015, 07:52 PM   #10
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,294
QuoteOriginally posted by Sluggo Quote
That's interesting. And "Vivitar" is/was just a marketing entity that never really manufactured any lenses, right? I wonder if their various suppliers have bent specifications in different ways or had varying quality control.

Even though my two 19mm lenses are the same model, they might have come from different manufacturers and have little in common other than similar-looking cases and the same published specs. Maybe one is really a Cosina inside and the other a Tokina or whatever.
Your lenses are old and the iris in one may be a little different than the other just from age (weak spring or some such) or there may have been a botched service attempt at one time. You might want to attempt to calibrate the lenses to each other or have a competent camera tech do it for you.


Steve
06-14-2015, 08:17 PM   #11
Site Supporter
Sluggo's Avatar

Join Date: Sep 2006
Location: Ames, Iowa
Photos: Gallery | Albums
Posts: 597
Original Poster
QuoteOriginally posted by Not a Number Quote
Vivitar indicated the manufacturer with the first two digits of the serial numbers:
Thanks for that. Both start with 9, so I guess they are Cosinas.

QuoteOriginally posted by stevebrot Quote
You might want to attempt to calibrate the lenses to each other or have a competent camera tech do it for you.
I doubt it will be necessary at this point, since I almost never use anything other than F8 or F11 for 3D shooting; if it turns out that the behavior is consistently compensatable (let's pretend that is a word) at those apertures, I can live with it. But otherwise yeah I might send them off to someone.
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!
3d, bodies, camera, cameras, dslr, exposure, iso, k20d, pair, pair of k20d, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Exposure and color matching three images StarDust Digital Processing, Software, and Printing 10 06-27-2015 11:13 AM
Fill the What? Full of What? I'm having trouble digesting this full-frame stuff... gdneil Monthly Photo Contests 22 05-16-2015 10:18 AM
Having trouble Kenny JL Visitors' Center 6 04-30-2012 10:48 AM
Having trouble with Diafine. Swift1 Film Processing, Scanning, and Darkroom 13 08-24-2010 02:58 AM
K20D+A28mm f/2.8 Exposure trouble max889 Pentax SLR Lens Discussion 2 01-03-2010 12:08 PM



All times are GMT -7. The time now is 03:04 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