Light Metering and Auto Focus

[flaclick]

Hi
I've searched the forum for my answer, but frankly it got me more confused, so I'm going to ask it anyway.

When you are trying to establish the correct exposure, it may be necessary to trick the light meter by pointing the camera to a different light source or object, like the sky. You then hold down halfway the shutter button and recompose. This where i get confused......if you point the camera to one object to get a meter reading the lens also at that time will focus (via autofocus)....if you then have to move the camera slightly down or sideways to get the main subject in view, won't you loose that sharp focus on the main subject. By holding the shutter button halfway, you lock focus. What if after recomposing, you need to re-focus? Letting up on the shutter button will loose the light meter settings you feel are correct? Am I making sense? Probably not....help! Does anyone understand what I"m trying to say?

Ruth

[OdiN1701]

You don't have to trick the light meter if you understand how much it might need to be "over" or "under" exposed for a particular shot. Example - when shooting in the snow you may have to have the meter at a +1 setting instead of at 0 because at 0 the snow will end up grey. Metering off of another area is just a matter of setting the shutter/aperture/ISO so that your meter reads what you want. You can then recompose and refocus and you don't need to worry about the meter because the exposure is already set. Maybe I'm not getting what you are asking but there shouldn't be a need to do what you are doing there.

Though, if you do AF somewhere else and recompose, your focus may be off. If your lenses are USM then you have full-time manual focusing, whether it's in auto or not and you can manually focus after recomposing (still holding shutter release halfway).

[TheSteveMadden]

That's what the Exposure Lock (*) button is for. This works easiest if you have partial metering set as you can really pinpoint the light you want to expose for.

If you've reassigned it to do focusing using C.Fn 04-1, then you can do the half shutter press to lock exposure and recompose. If you use C.Fn 04-3, then the exposure settings are determined at the point that the shutter is released and the half-press does nothing.

[flaclick]

Hi Guys
I'm still a little confused. If I want to take a pic of a sunset, I don't point the camera directly at the sun and click. To get a good exposure, I have read that you can get a meter reading from either the scene besides the sun or the light reflecting off the water. I guess I'm getting confused between exposure lock and exposure compensation. And I read that there are situations where you go +1 stop on EC, like snow. Is that the same thing as opening the aperature one full stop?

Does this make sense, cause I don't even understand what I just wrote :confused:

Thanks.

[OdiN1701]

Well for exposure lock, take this example. If you wanted a silhouette (sp?) of two people standing against a bright background, you wouldn't want to meter off of the people. So you meter the brighter background, lock that in, and then recompose on the people. If you expose for the people in that shot, the background will be completely blown out. In order to get the people and the background visible and exposed, you'd need flash for fill light.

You are right in snow you would want to adjust the exposure compensation. However, I personally don't use that. I know that a balanced meter reading is going to be off so I just shoot with the meter reading at +1 and don't bother with EC at all. It just depends on how comfortable you are. Sometimes I tend to just ignore the cameras meter completely or use a handheld meter to get what I want.

[flaclick]

When you say:

So you meter the brighter background, lock that in, and then recompose on the people.

what exactly do you do when you recompose? Do you refocus or just get what you want in the frame?

And how do you shoot a +1 meter reading without messing with EC?

Ruth

[OdiN1701]

Recompose means just that...compose the scene with the elements how you want them placed, and refocus as necessary.

Are you shooting in manual mode?

Basically what I mean is instead of getting the light meter right in the center, I adjust my settings (slower shutter speed, whatever) so that the light meter reads +1 in the viewfinder, and then take the shot.

[flaclick]

Thanks for defining 'recompose'. I had a feeling that's what it meant, but didn't want to assume.

The meter reading of +1 in the viewfinder must be a feature in the 20D, as in my 350D, I have to set the exposure comp manually to set it to +1. I usually shoot in Av or Tv or a few times P.

What got me started on all of this questioning is I"m reading the book Understanding Exposure by Bryan Peterson. It's a great book, but sometimes I need a little more clarification. Thanks for helping.

Ruth

[PhotosGuy]

Are you shooting in manual mode? Let me change that to read, "You should be shooting in manual mode." Then you only have to think about focus & composition.

[OdiN1701]

Thanks for defining 'recompose'. I had a feeling that's what it meant, but didn't want to assume.

The meter reading of +1 in the viewfinder must be a feature in the 20D, as in my 350D, I have to set the exposure comp manually to set it to +1. I usually shoot in Av or Tv or a few times P.

What got me started on all of this questioning is I"m reading the book Understanding Exposure by Bryan Peterson. It's a great book, but sometimes I need a little more clarification. Thanks for helping.

Ruth

Ahh! Okay if you are in Av/Tv modes then you will have to use exposure compensation because the camera will automatically select the Aperture/Shutter Speed (depending on which mode) in order to get the light meter to 0. In manual mode you have total control over the exposure, and if you know a scene needs say f/4 @ 1/125th, then you can just set it and take the shot, regardless of what the meter says if you know it's right.

In order to understand exposure, you should really shoot in manual mode as you then have full control. I still shoot in Av mode once and awhile at a wedding, depending on conditions, but mostly I use full manual for everything.

It might be a bit confusing, but you'll get it!

[flaclick]

Thank you so much for your help.

R

[Evy&Gaby]

OMG! This is EXACTLY what answers I was looking for! I too am reading UE and couldn't figure out what my "light meter" was supposed to be. I assumed it was what it is, but wanted to be sure, just like Ruth :) And the recompose question too! THANKS for asking this question! Now I "get" it :)

[gateruner]

Best thing for me was to take the exposure and the focal operations and make them separate buttons on the camera like Steve stated above. Back * button for focus and the shutter button to lock exposure. Takes a little getting used to but now it would bug me if it was any other way.

[ericgtr]

Let me change that to read, "You should be shooting in manual mode." Then you only have to think about focus & composition.
This is what I will sometimes do also. If needed I will use P mode to get a reading and exposure setting for the area I want to expose on, get all the readings, change it to Manual and utilize those settings freeing me up to compose and focus all I want without worrying about the rest. However, I have CF# 4-1 setup to keep my focus separate from my exposure in any other mode.