Exposure shooting RAW

[mivy00]

Ive been having some problems with my camera when I shoot in full auto mode I get a good exposure. but when I shoot in AV mode and bring the F stop down to 2.8 the picture is over exposed. Same on Program mode when i take the F Stop down I get an over exposed picture. I thought the purpose of AV mode was to allow me to set the Aperture then the camera would auto select a shutter speed to gain correct exposure.

I'm not sure but maybe I should set the camera to be using center weighted metering instead of average metering for my shots " would this help "?

[engstrom]

Originally Posted by mivy00

Ive been having some problems with my camera when I shoot in full auto mode I get a good exposure. but when I shoot in AV mode and bring the F stop down to 2.8 the picture is over exposed. Same on Program mode when i take the F Stop down I get an over exposed picture. I thought the purpose of AV mode was to allow me to set the Aperture then the camera would auto select a shutter speed to gain correct exposure.

I'm not sure but maybe I should set the camera to be using center weighted metering instead of average metering for my shots " would this help "?

Aperture priority should select an appropriate shutter speed to properly expose the image. What ISO are you shooting at? If you have a high ISO and are shooting in daylight the camera's fastest shutter speed might not be fast enough to properly expose.

[mivy00]

At first I thought that was the problem I was shooting at the highest ISO 1600 but I changed it to 400 yesterday and had the same result ....a over exposed picture should i try going lower ? I was shooting outside at about 4pm both days.

[engstrom]

Originally Posted by mivy00

At first I thought that was the problem I was shooting at the highest ISO 1600 but I changed it to 400 yesterday and had the same result ....a over exposed picture should i try going lower ? I was shooting outside at about 4pm both days.

Sunny 16 rule - at f16 you should have 1/ISO shutter speed. So, at f2.8 thats...5 stops more light then f16 so 5 stops more than 1/400 is....1/12800. Yeah, I'd say you need to drop the ISO down to 100 or even 50 for shooting at f2.8 on a bright sunny day.

[mivy00]

I wish there was an easy way to understand and remember how this all works .... I know my camera does 100 but i dont think it goes down to 50

[cmalana]

If it's still too bright, you can use a neutral density filter. When it is very bright out and I need to shoot with large apertures to create a shallow depth of field, you have to have at least 1 if not more ND filters.

Your camera manual will state your maximum shutter speed. If you go to Av and it's blinking, then you need the ISO lower. If you have ISO already at 100, then you have no choice but to close down the aperture.

[d2frette]

Originally Posted by mivy00

Ive been having some problems with my camera when I shoot in full auto mode I get a good exposure. but when I shoot in AV mode and bring the F stop down to 2.8 the picture is over exposed. Same on Program mode when i take the F Stop down I get an over exposed picture. I thought the purpose of AV mode was to allow me to set the Aperture then the camera would auto select a shutter speed to gain correct exposure.

I'm not sure but maybe I should set the camera to be using center weighted metering instead of average metering for my shots " would this help "?

Are we talking a few pixels getting overexposed? Is the whole luminance histogram moving right? If so, by how far of a shift are we talking about? Can you tell if it occurs in just 1 channel, or all three?

Here comes my theory:

Remember, we're using SLRs here. An SLR can't truely know the *exact* exposure for every pixel. So, a little clipping at EV0 is not uncommon.

To explain the shift, then, is just one step further. Not every pixel is the same at f16 as f8 for a given shot. Even more are different from f16 to f2.8. So the fact that you sometimes get a shift would not bother me. If you always get a shift, then maybe we should do some experimenting. And if the shift is slight, that's understandable. Shooting wide open could be causing enough blur to occasionally shift the histogram right, and thus cause some clipping.

[DEMDeepEllumMusic]

Why shooting wide open during the day? take the lens down to 5.6 or 8. If you are worrying about depth of field in focus seperate your subject from the background a bit further to get the effect (also overfocus on your subject just a bit to shift the in focus range of the depth of field to in front of and just back of the subject and not to where the subject is in the middle of the in focus range). Now if you are not worried about depth of field in focus take that lense and turn the F stop to 16 (generally in the best part of the lenses abilities).

Your variables-ISO setting (full sun turn down to 100 range), F-stop (smaller number means more light gets in 2.8 vs 16 vs 22+), exposure time (some cameras have a fastest exposure time in the 1/2000th of a second range).

So shooting in the Sahara at high noon on a cloudless day may have you at 100 ISO, F-16 and a 500th of a second while shooting on a snow covered mountain top the same day may have you even at 1,000th of a second (more reflected sunlight).