Inaccurate metering at slower shutter speeds w/ MF lenses?

[thearne3]

Hi,

I just noticed that my E-P1 does not seem to expose properly with MF lenses when the shutter speed is less that 1/15 or so. I noticed this when testing two lenses and it's the same with both.

I set up a tripod and took sequential pictures with each lens. Camera set on aperture priority. Starting at f2.8, I opened the aperture a full stop (2.8, 4, 5.6, etc) with each picture. The starting shutter speed was about 1/13 at ISO 400, then 1/10, then 1/6, etc. I believe the shutter speed should have been cut in half each time, shouldn't it? In any case, the pictures were indeed progressively underexposed.

This does not occur with AF lenses.

Can anyone explain this?

Thanks,
Tom

 

[PeterB666]

I have found that the meter becomes inaccurate with small apertures (i.e. large f numbers). Wide open and for the first couple of stops, all my MF lenses are fine.


The lenses I have are 28/2.8, 50mm/1.4, 50mm/3.5 macro, 200mm/4 OM lenses and a Schneider 40mm/1.9.

The 28mm lens seems pretty good at most stops and I have no real issues with the 50mm macro either or my 40mm Schneider lens.

The longer the focal lenght the bigger the problem but as I don't have a huge collection of lenses, that chould just be a coincidence with my kit.

 

[thearne3]

Seems to be more about shutter speed for me...

Peter,

Interesting observation. For me the phenomenon seems to be more shutter speed related, eg, using a 40mm lens (80 equiv), I'm seeing it at 5.6 and 8 - not usually considered small aperture levels. At higher light levels, I get good exposures right up to f11 (haven't tried higher).

Will continue to experiment...looks like changing from ESP metering to center weighted fixes the issue??

Best,
Tom

 

[PeterB666]

I only use centre weighted metering. I know spot metering is supposed to be a problem.

The times that I have noticed the problem have been at night when I am using the camera in M or A when I focus at wide open and then stop down.

 

[thearne3]

Peter,

Your note confirms what I had noticed: center weighted seems less sensitive to the issue. It would be nice to understand the 'why', but in the meantime, we have a decent solution.

Best,
Tom