Inconsistent exposure of a A-modified K24/2,8

klaus123 · 06-03-2013, 10:52 AM

Hello

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 http://klaus-takes-pictures.blogspot.de/

Last edited by klaus123; 06-03-2013 at 10:57 AM.

demp10 · 06-03-2013, 11:11 AM

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 that’s where the discrepancy exists.

klaus123 · 06-03-2013, 11:15 AM

@demp10: Your explanation fits the K7 behavior (which I expected) but not the K01 results

carrrlangas · 06-03-2013, 12:39 PM

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 won´t 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"

06-03-2013, 10:52 AM	#1
klaus123 Senior Member Join Date: Apr 2011 Location: Germany Posts: 238	Inconsistent exposure of a A-modified K24/2,8 Hello 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 http://klaus-takes-pictures.blogspot.de/ Last edited by klaus123; 06-03-2013 at 10:57 AM.

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06-03-2013, 11:11 AM	#2
demp10 Veteran Member 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 that’s where the discrepancy exists.

06-03-2013, 11:15 AM	#3
klaus123 Senior Member Join Date: Apr 2011 Location: Germany Posts: 238 Original Poster	@demp10: Your explanation fits the K7 behavior (which I expected) but not the K01 results

06-03-2013, 12:39 PM	#4
carrrlangas Veteran Member 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 won´t 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"