exposure compensation

I've read in a few places about Exposure Compensation (EC), and have experimented with it a few times, but I don't understand the need.

I may be missing the point, but if you shoot in manual mode you can stop down or open up aperture, or speed up or slow down shutter.

If you are using a program mode and have to press buttons to adjust EC, wouldn't you be better off using manual?

Is there something (else) I don't understand here?

Thanks for you help.

A light meter, including the one built into a camera, integrates the reading it makes to make an average overall grey (18% reflectance). In other words, it assumes that the scene will, on average, be overall grey.

Suppose you have a grey wall filling the viewfinder. The picture will indeed be grey and will turn out grey.

If the wall was white the camera would think it was too bright and would reduce the exposure so the wall truned out grey. But you want it white, so you use exposure compensation to increase the exposure given.

If the wall was black the camera would think it was too dark and would increse the exposure to make it grey. You want it black, so you use esposure compensattion to reduce the exposure and render the wall black.

A real world example is snow, and we have seen a few examples of this on this forum recently. If you meter as normal the snow turns out grey for the reason given above. So you need to use exposure compensation to render the snow white by increasing exposure.

You can experiment with different subjects and see the outcome on the histogram. With experience, you will know hoe much to compensate by to obtain perfect exposure.

Whole books have been written about this. The classic way to approach it is via the Zone System, but I will spare you an explanation of that for now.

Hope that helps!

True, shooting manual means you would never need to use exposure comp.
That's why I always shot in manual when I used slides, it was quicker than fiddling with buttons.
But a lot of people shoot in Av mode for quicker work... you just point, frame focus shoot, and meter does it's own work. Hence the need to override the meters readings at times, as John described.
Some situations happen fast and using manual metering will sometimes cost you the shot while you are busy making adjustments.
But if you are doing something like landscape, you have the time to do detailed metering and manual would work great here.
But lets say you are shooting snow leopards in the mountains... you need to work fast! So you can preset the meter to Av and add a +1.5 exposure setting (to compensate for snow) and shoot away as the action unfolds, and the meter will make any fine adjustments on its own. If you were in manual mode you may need to adjust constantly if the leopard is moving in and out of shade and sunlight.
We've all been there before eh!

Bloody snow leopards! They keep harrasing my goats!

Thanks peeps,

So, for slow, leisurely work, I can carry on and use manual and adjust as needed.

For faster changing conditions use Av (or most suitable program mode) and alter EC to suit.

There is no need for any of this faffing about, just take an incident reading IE the light falling on the subject rather than reflected by it and a perfect exposure every time is guaranteed!!!

Ken

of course the snow leopard will either be several miles away or have decided you look tasty by the time the shot is set up.....

Yeers... There is no way I'm going to wave my arm about just in front of a snow leopard, or any other wild animal in fact!

And by the time I've trudged from my shooting spot to the other side of the valley to take a landscape shot, someone will have nicked me camera!

I honestly cant see any problems shooting snow leopards, the people across the road from me keep two in their house - true, no kidding - but thats footballers and their wives for you. Just come to Glasgow and it'll be easy as shooting fish in a barrel so long as you get the exposure right

Ken

mmm I always have trouble with the reflections off the surface of the water when I try shooting fish in a barrel, perhaps I need to invest in a polariser

Some lenses require a permanent EV correction of say 0.3 ... 0.7.
It is easier to dial this in only once and then work with the automatics than to use M all the time.

Its not polar bears we're talking about now is it?
Ken

no, I tried using a Polar Bear as a substitute for a Polariser. He proceeded to splash around in the barrel making it even harder to see through the surface and then are all the fish