Spot metering vs evaluative?

MommyOf4 · Jan 11, 2012

Hi, guys

Up til now I pretty much always keep my camera on evaluative metering but, yesterday I was messing around a little bit with spot metering. I found that a lot of my pictures were coming out over exposed when spot metering. I hear a lot of people say to meter for the subject's skin but only 50% of my pictures were correct exposures. What am I missing here? Is there certain times where spot metering is more useful then evaluative? I was shooting indoors with low light and a high ISO.

tirediron · Jan 11, 2012

Spot metering is just that; the metering of a very small spot. Read your camera's manual for the exact details, but it's usually less than a 5 degree beam, therefore, if your metering point rests on a small, dark area when the rest of the scene is very light, it will comeout overall much over-exposed. Generally, spot-metering is used when there is a small area of a scene which is lit much differently than the majority, but which needs to be correctly exposed. Most commly for heavily backlit subjects... say you have a person with the sun behind them, if you used evaluative metering, their face would most likely be very dark. To overcome that, you would spot meter the face. This would cause the rest of the scene to be blown, but the face would be correctly exposed.

MommyOf4 · Jan 11, 2012

Thanks, tirediron! That makes complete sense

......back to the manual I go.....

Big Mike · Jan 11, 2012

The big difference between spot metering and evaluative, is that spot reads one small area, and ignores the rest of the scene. So the reading you get, is entirely based on that small area.

That's the easy part. Getting proper exposure doesn't come down to which metering mode you use. It has to do with how you interpret the meter's readings with regard to what your metering off of.

In case you didn't know (most don't), a camera's meter isn't designed to give you proper exposure. (I'll let that sink in for a minute)
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.
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A camera's meter is designed to give you an exposure for middle grey. So it only gives you 'proper' exposure when you are metering off of something that is middle grey (or something that averages out to middle grey if you're metering on more than a small spot).

So if you spot meter on someone's face...you will only get 'proper' exposure, if that person's face/skin is close to middle grey (in tone, not color).

So what you need to do, to get proper exposure, it to either give the meter what it wants (meter off of a grey card, for example). How to use a Grey Card ~ Mike Hodson Photography
Or you could meter off of something and make an educated guess as to how far off of middle grey that something is. For example, you could meter off of white snow, and guess that it's about two stops brighter than middle grey. So adjust your exposure to two stops above the meter's reading. You could meter off of green grass or foliage and in many cases, it's fairly close to middle grey. There are plenty of 'rule of thumb' type things but with a bit of understanding and experience, you can meter off of just about anything and make an educated guess that should get you pretty close.

xposurepro · Jan 11, 2012

Spot is also great for creating dramatic atmospheres. Use harsh light and spot meter for those areas letting everything else fall into shadow.

MommyOf4 · Jan 11, 2012

Big Mike said:
The big difference between spot metering and evaluative, is that spot reads one small area, and ignores the rest of the scene. So the reading you get, is entirely based on that small area.

That's the easy part. Getting proper exposure doesn't come down to which metering mode you use. It has to do with how you interpret the meter's readings with regard to what your metering off of.

In case you didn't know (most don't), a camera's meter isn't designed to give you proper exposure. (I'll let that sink in for a minute)
.
.
.
A camera's meter is designed to give you an exposure for middle grey. So it only gives you 'proper' exposure when you are metering off of something that is middle grey (or something that averages out to middle grey if you're metering on more than a small spot).

So if you spot meter on someone's face...you will only get 'proper' exposure, if that person's face/skin is close to middle grey (in tone, not color).

So what you need to do, to get proper exposure, it to either give the meter what it wants (meter off of a grey card, for example). How to use a Grey Card ~ Mike Hodson Photography
Or you could meter off of something and make an educated guess as to how far off of middle grey that something is. For example, you could meter off of white snow, and guess that it's about two stops brighter than middle grey. So adjust your exposure to two stops above the meter's reading. You could meter off of green grass or foliage and in many cases, it's fairly close to middle grey. There are plenty of 'rule of thumb' type things but with a bit of understanding and experience, you can meter off of just about anything and make an educated guess that should get you pretty close.

I'm going to read this over about 100 times now until it sinks in lol. TY

MommyOf4 · Jan 11, 2012

xposurepro said:
Spot is also great for creating dramatic atmospheres. Use harsh light and spot meter for those areas letting everything else fall into shadow.

I did learn that yesterday

That picture I took of my son in my new avatar was done with spot metering. I do like that its giving me another tool to be creative!

Big Mike · Jan 11, 2012

I could go on and on...that was only a little snipit of the huge topic that is Metering.

But more than half the battle is knowing that the camera isn't designed to get proper exposure...and once you know that, you can adjust your exposure away from the camera's recommendations (the zero on your meter/scale).
If you use auto modes, you can use EC (exposure compensation) or if you use manual mode, you can just change the three exposure settings to get the 'needle' where you want it.

KmH · Jan 11, 2012

In other words, Spot metering is much more accurate than Evaluative metering is since Evaluative metering averages all the reflected light in a scene while spot metering only sample a very small portion of a scene.

Spot meteing mode can be used to measure the reflected light from several portions of the scene to be imaged. With those additional Spot mode meter readings the photographer can them make a more informed decision on how to adjust the exposure.

Note that the in-camera light meter only measures reflected light. In photogrpahy it is sometimes very beneficial to also measure incident and/or strobed light (flash).

analog.universe · Jan 11, 2012

I'll most often use spot metering in manual mode, as opposed to either of the priority modes, but there are exceptions. If I'm shooting manual, I can use spot to meter the highlights, meter my subject, meter the shadows, just get a general idea of what kind of light I'm dealing with. I can adjust settings appropriately and keep them from photo to photo. Evaluative metering I find most useful in either Av or Tv. It is a little more complex than simply averaging the scene (there are averaging modes for that), but it's capability varies from camera to camera. Evaluative allows you to use EC and allow the camera to make adjustments based on a changing scene, it doesn't matter if the subject isn't in the center where your spot meter is etc... There are of course exceptions to everything and times when spot is useful in Av and Eval is useful in M and all that.