Under exposing in Raw

[rbarry]

Originally Posted by wadooz

Hi Gang, just reading Andydo's thread about his under exposed Wedding shot. I use a Canon 450D and usually shoot in Raw. I was advised to deliberately underexpose in Raw to give me a faster shutter speed. The reason given was that it's dead easy to tweak it in Camera Raw or Lightroom 3 to bring out all the detail. Was this good advice or am I losing something by not getting it right in camera?
Cheers.
Martin.

You've had some great advice from those better qualified than I, but one point that hasn't been raised is what mode you're shooting in and what settings you've used to underexpose an image. I had a Canon 400D, and now own a 550D. I can't remember for sure if all the variables listed below applied to the 400D, but from memory they did in the main, and so will be the same for the 450D.

If you were in P (program) mode, exposure compensation will affect both shutter speed and aperture value.
If you were in AV (Aperture Value) mode, exposure compensation will affect shutter speed but not change the aperture value.
If you were in TV (Time Value) mode, exposure compensation will affect the aperture value but not the shutter speed.
If you were in M (Manual) mode, by default, exposure compensation will affect shutter speed and not aperture value.

In addition, if you set the ISO manually it will remain the same value. However, if you set ISO to Auto, the ISO will change to maintain the correct exposure up to the point where Auto ISO limits are set. Beyond that it will change either aperture or shutter value, dependant on the rules above.

So if it's shutter speed you are trying to maintain, make sure your camera is set to TV mode when invoking exposure compensation.


I can't account for how other manufacturors design their camera bodies for these methods of exposure compensation, although I imagine it would be the same.

[wadooz]

Wow! Thanks rbarry, that's a lot to take in but I'll just let you know what I've been using up to now.
I usually shoot in AV mode and have been under exposing by up to one stop by pressing the AV +/- button and scrolling with the wheel. If I up the ISO I make sure it's set where I need it, not relying on Auto mode. I haven't yet tried under exposing in any other setting.
I haven't been trying to "maintain" the shutter speed, I've been after a faster one to compensate for a shaky hand, (which I'm working on thanks to advice from jet_kit) especially when I'm at a long focal length.
However, after taking advice on this site I'll not be under exposing very often any more. I know there are times when I'll need to because of the conditions but generally speaking I'm better off getting it right in camera and fixing my shaky hands.

I went out this afternoon and practiced the shooting techniques advised by rbarry and experimented with things advised by cathus. I've yet to check 'em on my pc 'cos crickets just starting and it looks like another Indian flogging so it might have to wait a while. I'll get into it again tomorrow.
Thanks very much one and all.

[rbarry]

Hi wadooz,

The point I'm making is that you want to maintain a set shutter speed to suit your ability to hold the camera steady enough at a given focal length, to produce as clear, and shake free image as you can.

For example, in choosing TV mode you want to premeditate the shutter speed that would give you the best chance of getting a shake free sharp image.

You want to capture an image of something in the distance at a focal length (zoom rating) of 200mm, you would need to maintain a shutter speed of at least 1/200sec. Maybe it would be wise to increase that value to 1/250sec to compensate for additional camera shake. If the image you are trying to capture also has movement that you would like to freeze, you may want to increase the desired shutter speed to say 1/350sec depending on what the subject material is. Lets say with the ambient light of a summers day you chose a fixed ISO of 100, the camera meters the light with a fixed shutter speed of 1/350sec and that results in an aperture value of f14.
You then realise that the sky or reflections in the foreground water (picture the scene!) are going to get blown out. Invoke 1 stop of negative exposure comensation. If that's no good try another. Get home and look at the results: the shutter speed would have remained the same because you were in TV mode, but the aperture would have closed down by 1 stop to f16 in the first image and by 2 stops to f18 in the second. They will be under exposed but they should be sharp and crisp, with the possibilty of rescuing them in post. If you did the same in AV mode the aperture would have remained at f14 but the shutter speed would have reduced and be more likely to end up in a blurred image.

You can be more creative in AV mode with dof (depth of feild) and nice bokeh effects (soft distant backgrounds), and its possible to adjust the settings in the same way, but you would have to keep an eye on the shutter speed as that will be the first thing to reduce if you wanted to dial in negative exposure compensation.

[wadooz]

Thanks again rbarry, I can see where you're coming from now. My thinking was that by opening the aperture as wide as possible, I would achieve the faster shutter speed anyway and also blur out any distracting background. We don't have as much trouble with poor light down under as you do up top so unless I particularly want a large dof I keep the aperture fairly wide.
I will try and remember to use the rule of thumb (one over the focal length) and increase it when necessary to gain a sharper shot. I've read your post several times and it's helped me a lot. I must spend more time thinking about my shots and settings.
I'm getting there.
Cheers.
Martin.

[OldBoy]

On my Nikon I use minus 0.3 setting all the time to give me the best results.