Photoclubalpha

Hi there,

I'm new here, but I have been looking in the forum for quite a while, -insert generic introduction here-. You all know the drill

Anyway I have been a a700 user for quite a while now, and recently I have been noticing some strange behaviour with the camera in low light (with some backlight, I think).
I started noticing it after I installed the v4 firmware and thought it might have something to do with that, but writing this post now and processing the pictures, it also occured to me that all the pictures that show this behaviour were shot with a minolta 20mm 2.8. So it might have something to do with that as well.

So here is the problem. I was playing with my new lens in my room and i shot two, almost identical pictures. One is exposed properly and one is horribly under exposed. Note that there is a candle in the room and that the difference in the composition is only a slight movement to the right.
Both pictures were taken at iso 3200, F2.8, 20mm, DRO off, high iso nr normal, and the metering is on multi-segment. The first one exposed 1/40 of a second, the second 1/3. I know that it are bad pictures, and it is bad lighting, but still I found it very strange, and quite annoying (see later in the post). Also I was able to reproduce the problem by shifting the composition only slightly.

I think it has something to do with the multi-segment metering and perhaps the focus point. Later I did another small test with a flashlight. I don't know if it is valid test, but there the same behaviour can be seen. I these shots the focuspoint was the outermost right focuspoint near the flaslight. I locked focus and then pushed the af/mf button so the camera metering isn't locked anymore. again with the slight shift there is a completely different exposure. 1/5 against 1/25 s
(please see the second post for these pictures as 3 is the maximum number of files I can attach)

Are any of you having problems with low light exposures with firmware v4 or perhaps the 20mm 2.8? Can it be a bug in the firmware or a problem with the lens, or is this behaviour normal?
as I mentioned above, it is not only in these weird situations. the shot below is also underexposed quite a bit, and this is a situation in which a correct exposure should be possible (a few others of this series are exposed correctly, but quite a few significantly underexposed.), and in this situation it was quite frustrating. Again there's multi-segment metering, F2.8, iso 1600, focus point on the guy. You can see that again there is some backlight in the picture, but not so bad that it can't handle it, i thought? Since the behaviour is irratic, it is not possible to simply expose say a stop to the right (also the under exposure is well over a stop).
I hope you guys can shed some light on the issue, perhaps i'm missing something elementary..

regards,
ote

the flashlight pictures:

Your guess is correct - multi segment metering and focus point. Try centre weighted instead, or even use spot metering.

David

Thanks David,

for the quick reply. It is appreciated.
So I can conclude that this behaviour is normal in these situations (backlight, and low light)..

I can understand that the camera tries to expose correctly for the focus point, but in real world shots, like the shot of the guy, it still seems a bit weird. I seem to remember that the (center)focus point was on him and that I then recomposed a bit, this would mean it should try to expose for his skin, right? Instead it still exposes for the background.
I could be mistaken though, but i think that is what i usually do in those situations.

Anyway, I will try your solution. Thanks.
ote