Problems using aperture ring

robbie_d · 2010-02-22T21:50:05+0000

Hi all, Just having a play with my Pentax-A 28mm f2.8, using the aperture ring to select aperture rather than using the camera on 'A' setting (doing it to get some practice in advance of receiving a Pentax-M 135mm f3.5 I've purchased off the classifieds). Firstly, using the aperture ring set at 'A', and in Av mode I lined up a shot at f2.8 and made a note of the shutter speed (and other settings) the camera suggested. I then went to M mode, used the settings I had noticed and took a picture. Picture looked good, all exposed properly. Then, changing the aperture ring to 2.8, I used the same settings as previous, but the shot looked very different, not necessarily underexposed, but just more yellow. Here are the pictures (don't judge me :D, they are very quick and rough for testing only!): I then tried a longer exposure on the second picture but it began to look a bit glarey and overexposed. Does anyone have any idea what is wrong/what I'm doing wrong?

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Canada_Rockie... Canada_Rockies

36 posts
17 years
Canadian Rocky Mountains

Posted 25/02/2010 - 20:18 Link

Kris, that was the problem I was having, and what we are discussingin this thread. Others on another forum of which I am a member (PentaxForums.com) suggested that substituting the screen from an *ist D would resolve the problem with wonky metering on my K10D. I tried the LL-60 *ist D grid screen (I use grid screens in all my cameras), and it did resolve the problems with my two M lenses, the 100/4 macro and 400/5.6 telephoto. They now meter as expected across the entire range.

There was some discussion that the problem was not with the metering but with the mechanicals that stop the lens down not being linear with the older lenses and linear with the DA series. I took a series of shots with the 400 using "Sunny 16" exposures, and all were the same. They are here

Flickr 400 exposure test

Albert in the Canadian Rocky Mountains
K3, M 400/5.6, M 100/4 macro, DA 12-24, DA* 16-50, DA L 55-300
FA 24-90, 1.7X AFA, 1.4X-S
AF 540 FGZ flash