Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
06-03-2013, 10:52 AM   #1
Senior Member
klaus123's Avatar

Join Date: Apr 2011
Location: Germany
Posts: 234
Inconsistent exposure of a A-modified K24/2,8


This is a x-posting from the lens section, but because of the specific K0-issues

During the last day I modified a manual K24 to Auto-Mode

Using a K7 it can be adjusted from 2,8 to 22 (as it should) and exposure is quite OK, BUT the results on my K01 are surprisingly inconsistent..........

More Details at

Last edited by klaus123; 06-03-2013 at 10:57 AM.
06-03-2013, 11:11 AM   #2
Veteran Member
demp10's Avatar

Join Date: Jun 2011
Location: Atlanta
Photos: Albums
Posts: 602
With modified K and M lenses you can get correct exposure metering only wide open (at F2.8 in your case) or closed down (at F22).Anything in between will be off. The reason is that the camera moves the aperture lever in linear steps to set the F-stop. On pre-A lenses the lever movement is linear to the diameter of the iris. For A and later lenses it is linear to the area of the iris which is the correct relationship.

Essentially the camera meters wide open, and knows the range from the contacts on the lens. When you set an F-stop in the body, the camera will calculate the position of the level (in linear steps) to close down the lens to the selected F-stop and thats where the discrepancy exists.
06-03-2013, 11:15 AM   #3
Senior Member
klaus123's Avatar

Join Date: Apr 2011
Location: Germany
Posts: 234
Original Poster
@demp10: Your explanation fits the K7 behavior (which I expected) but not the K01 results
06-03-2013, 12:39 PM   #4
Veteran Member
carrrlangas's Avatar

Join Date: Mar 2012
Location: Joensuu (Finland)
Photos: Gallery
Posts: 1,761
K-01 works in liveview mode full time and in order to protect the sensor from too strong light, the camera closes the lens aperture as needed. So when you "cheat" saying the lens is A type, the camera meters with the lens aperture closed to a value that has nothing to do with the actual settings. The metering will always be off becouse the aperture lever on K or M lenses is not linear as in A and newer type lenses.
Also, the error wont be consistent as the camera will choose different "metering aperture value" according to the light value (LV) of the scene. You could try shooting in dark conditions, so the camera chooses f/2.8 as the "metering aperture value" and see if in that case the overexposure is consistent for your "chosen aperture value"


  • 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!
exposure, k-01, k01, mirrorless, pentax k-01
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Modification of a K24/2,8 to "A" klaus123 Pentax SLR Lens Discussion 7 06-03-2013 04:10 PM
For Sale - Sold: The ultimate Macro Set:Pentax A 100mm 2.8 and A 50mm 2.8 jjdgti Sold Items 4 09-27-2012 07:19 AM
A modified FA 100mm f/2.8 macro Asahiflex Pentax SLR Lens Discussion 5 08-05-2008 02:05 PM

All times are GMT -7. The time now is 09:53 AM. | See also:, 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?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]