Why is a SLR camera's auto mode so bad at proper exposure when it uses the same light meter as me in manual?

Question

Why is a SLR camera's auto mode so bad at proper exposure when it uses the same light meter as me in manual mode?

Answer 1

You might have a malfunctioning sensor somewhere in your camera. Has it always done this, or did it just start? How old is your camera? Has it been bumped around lately?

Take it to the store where you bought it and have them look it over. If it's still new enough, you can have it serviced under the warranty.

Answer 2

Hi,

it may not indicate a faulty camera. When a camera sets its own exposure (auto modes) it uses very complex algorithms to do so.

SLRs also tend to use specific points in the scene to determine exposure, they don't measure the scene as a whole.

Most common is "centre weighted" exposure. The camera assumes your subject is in the centre of the scene and places more emphasis on this area than the surrounding area.

But, these can be fooled by the prevailing lighting conditions.

As an example, bright conditions (such as snow, or on the beach) end up notoriously underexposed by cameras. This is because the camera is measuring the light at the centre of the scene, sees it is bright, and a fast shutter speed/small aperture is the result. This ends up in an underexposed photo.

The usual practice is to bracket scenes with tricky lighting - take three shots, one slightly over exposed, one in the middle, and one slightly underexposed. Your SLR manual will tell you how to do this.

Also check the manual for your camera's metering modes. They usually have an "overall scene" mode (uses a lot of points to measure light), a centre weighted mode, and a "spot" mode - this concentrates right inthe middle of the scene.

You might well ask why camera manufacturers have these centre weighted modes? It's useful because it means you can meter for your main subject in a scene, ensuring this is properly exposed, at the expense of the brightness of the scene as a whole.

If you want to find out more about exposure there's a good page here;
http://www.digital-photography-tips.net/understanding-exposure.html

There are also some links there to understanding shutter speed and aperture.

Finally (sorry to go on!), I'm assuming your SLR is digital? If so, take some test shots in different lighting conditions and vary the over/underexposure setting on your camera to see what works best.

Answer 3

I agree with Terisu. Something must be off. Frankly, all of my SLR's do just about as well in either Manual or Auto as far as metering accuracy goes. I mean, I can always finesse a reading and zero in on exactly the exposure I want, but I would never describe the Auto mode as "so bad" the way you have.

Answer 4

You have to take into account that it's not only the same light meter that the camera is using. You have to think about color termpature, ISO speed, white balance, and other things. The auto mode does not take into account all these things like a professional photographer can.

Answer 5

Depends what your metering on. Do you have examples? Take test shots of the same picture in manuel and in auto and meter the SAME SPOT. Dont meter a totally different spot and do it around the same time. Manuel you have more control over the shutter speed so that might be a factor in why its not properly exposing. If you have examples it might be nice.

Answer 6

I agree with Terisu & Dr Sam. Your exposure should be very close on auto, unless you're always shooting dark horses against white snow or something. Maybe get it checked out.