Metering on 20D?!?!?!

[RbrtPtikLeoSeny]

Hello everyone, I'm having some trouble understanding this selective metering thing.... There's evaluative metering, partial metering, and centerweighted average metering, but what do they all do? When should each be used and why?

Thanks for any help!:lol:

[tim]

Have you read the manual? It's brief but helpful. Here's my 30 second explaination:
- Evaluative - tries to get everything you see in the viewfinder in the shot well exposed. If there's a single bright light source it will expose for that and everything else will come out dark.
- Partial - makes sure the centre 9% of the photo is exposed correctly. Useful if there's a significant difference between the main subject of the photo and the rest of the frame.
- Centre weighted: partial with a bit of attention paid to what's outside the frame.

Have a play, the best way to learn is to do :)

[tim]

btw once you start using a flash all bets are off and everything changes. I haven't fully worked that out yet, it's more difficult to master flash photography.

[RbrtPtikLeoSeny]

Yea, the manual didn't really help me all that much. I just don't understand what type of situations each should be used for. That's all.

[tim]

Evaluative should be your default, and partial if there's a particularly bright or dark background behind the main subject, or naked lights in the viewfinder. Centre weighted I don't use much.

[robertwgross]

Yea, the manual didn't really help me all that much. I just don't understand what type of situations each should be used for. That's all.

Get over into the flash section of the forum and read the stuff written by scottbergerphoto.

I think he is getting ready to teach the summer session in advanced flashography.

---Bob Gross---

[robertwgross]

I can think of one case when I use center-weighted metering.

Sometimes I am going after wildlife that is way out there. It's so far out that I am using my longest lens, and even then it is not filling up the frame at all. I'm going to have to shoot and then crop the wildlife subject in the computer. Well, I really don't care about the exposure values for the stuff around the outside of the frame. All I care about is the exposure around the center. So, I stick the metering to center-weighted, and that works.

---Bob Gross---

[PacAce]

I can think of one case when I use center-weighted metering.

Sometimes I am going after wildlife that is way out there. It's so far out that I am using my longest lens, and even then it is not filling up the frame at all. I'm going to have to shoot and then crop the wildlife subject in the computer. Well, I really don't care about the exposure values for the stuff around the outside of the frame. All I care about is the exposure around the center. So, I stick the metering to center-weighted, and that works.

---Bob Gross---
I think what you really need, then, is to shoot in partial metering mode, Bob, so that everything but the center of the frame (9 degree FOV) is ignored. With CWA metering, although the central part of the frame is giving more importance to the metering, reading from the whole frame is still taken and considered in determining the exposure to be used for the shot.

[RbrtPtikLeoSeny]

Alright, this is starting to make some more sense..... thanks for the specific examples! Very helpful. Keep em comming.

[aam1234]

What about AEL (the "*" button) and metering. Does it use partial.

[CyberDyneSystems]

On the 20D "Partial" is the smallest pattern available, I find that partial is best ofr anbout 90% of what I shoot,.

[RbrtPtikLeoSeny]

So confused. o_O

[aam1234]

Why are you confused. Look at it this way.

Evaluative metering: The camera meters the whole frame.

Center weighted average metering: Same as above but with a bias towards the center.

Partial metering: Meters a small part of the frame.

[PacAce]

Why are you confused. Look at it this way.

Evaluative metering: The camera meters the whole frame.

Center weighted average metering: Same as above but with a bias towards the center.

Partial metering: Meters a small part of the frame.
For Evaluative metering, I would add that after the camera meters the whole frame, it analysises the frame to determine where the main subject is (indicated by the AF point). It then checks a database to try to determine what type of a scene the camera is actually looking at and then comes up with a exposure solution the camera thinks is suitable for the scene at hand. There's a little bit of intelligence built into the evaluative metering mode and hence, for most scenarios, is the most suitable mode to use.

The other metering modes have no intelligence built in at all.

[RbrtPtikLeoSeny]

I understand what each does.... I'm just confused about when to use each one.... I'm just looking for some examples of when to use each setting. That would really help, like what RobertwGross posted. That's what I'm looking for. Thanks.

[tim]

I understand what each does.... I'm just confused about when to use each one.... I'm just looking for some examples of when to use each setting. That would really help, like what RobertwGross posted. That's what I'm looking for. Thanks.

I suggest you read this thread again, from the start, things are explained in terms about as simple as you'll find anywhere. If we have to resort to giving you pictures and telling you which metering mode to use you'll be operating from memory not from understanding, which means you'll not be able to adapt to new situations easily.

[robertwgross]

Here is a quiz:

Guess which metering mode should be used for best results.

1. You have a wide stage, and you are shooting from row twenty with a wide angle lens. Only one spotlighted star performer is on stage, so he fills up only a small part of the frame.
2. You have a wide stage, still row twenty, still a wide angle lens. Now there are ten spotlighted performers running around, and there is some interesting stage lighting on the backdrop.
3. You have the same wide stage, still row twenty, still a wide angle lens. This time, there is a concert orchestra of about 75 members wearing black and white with shiny brass instruments visible.

---Bob Gross---

[tim]

4. You have a wide stage, still row twenty, still a wide angle lens. Now there are ten performers sitting down on the stage, wearing dark suits, and there's a naked bulb visible through the viewfinder.

[pvonk]

There's a little bit of intelligence built into the evaluative metering mode and hence, for most scenarios, is the most suitable mode to use.

The other metering modes have no intelligence built in at all.

I've been reading John Shaw's Nature Photography Field Guide on landscape photography and he has some interesting comments on metering (his book is aimed at film, not digital, but his film camera has the same types of metering).

Anyway, his discussion is on understanding exposure and using exposure compensation to get neutral objects to come out neutral. He does not suggest evaluative metering, since the camera makes all the decisions and thus you have no idea how to compensate to correct potential incorrect exposures. An example is taking a snow shot - spot meter the snow and lighten it 2 stops. If you don't compensate, the meter system makes the snow neutral (dull gray).

I would recommend this book to anyone having a hard time understanding exposure. Shaw really presents things in a clear way.

[robertwgross]

John Shaw has some good books. I have a couple, but they are fairly old, and they are purely film-related.

Film metering and digital metering can seem very similar, but when you get into flash metering, lots of it changes.

I should probably check out Shaw's newer stuff.

---Bob Gross---