Understanding Exposure

[winterminute]

I'm reading "Understanding Exposure" which is a pretty decent book. It feels really dated and some of the shots are pretty dated as well, but overall the content is pretty useful. I'd like to see more focus on Digital cameras, but generally the exposure triangle is the same for Digital and Film but the other tidbits of information are different. Overall, it is a helpful book.

But I'm left with a few questions around exposures...

1) Does the camera do any metering when shooting in manual mode?
2) What's the best type of metering?
3) I've read that you should set your exposure -1 or +1 (I can't remember which) if you're shooting digital, any truth to this?
4) What is EV? Is it a universal number or a relative number based on how far away you are from a correctly exposed shot? Or is this a value your camera produces that changes from camera to camera?
5) When they talk about correctly exposed shots, do they mean an EV of 0?
6) HDRs confuse me When they' talking about taking multiple shots for HDRs, they talk about taking it -1/0/+1. From what I'm reading there are only 3 factors in exposure (duh, the exposure triangle), but I don't understand how I can change any of them without changing the "feel" of shot which would create problems when I merge them into a single HDR.
-- Longer exposure would create streaks
-- Larger DOF would change what was in focus vs out of focus
7) What's a DOF calculator? When would I use one? Is this a mathematical equation I use on site or something that a camera tells you.

I'm at the stage where I want to learn the underlining theory and logic behind some of these settings and techniques, so feel free to hit me with the nitty gritty.

Thanks!

[Nicole]

Some of these answers may be opinions, but I'll try to support them with links for you You've got a lot of questions

Originally Posted by winterminute

1) Does the camera do any metering when shooting in manual mode?

It should unless it's a camera without a light meter built in. I would guess that your camera has some sort of meter that it will show you when you're in manual mode. It should look something like +....0....- or something similar to that. It seems like most people who shoot digital (me included) do not know what the proper settings for a perfect 0 are by heart. Plus there's always the use of artistic sort of things like really shallow depth of field where you'd want a faster shutter speed than a formula might say.

Originally Posted by winterminute

2) What's the best type of metering?

That depends on your personal preference and the scene that you're shooting. If you understand the various metering modes, you'll be able to better select which one you want to use for the given situation. But basically, what the camera is looking for is medium grey given the scene and the area that you've told it to look at. If you tell it to look at the whole scene (matrix / evaluative metering) you will get a different result than if you just have it look at one place (spot metering).

Originally Posted by winterminute

3) I've read that you should set your exposure -1 or +1 (I can't remember which) if you're shooting digital, any truth to this?

I think that this one depends on the camera. But I also think that those numbers seem really extreme based on my shooting habits. With my camera I tend to underexpose by 0.3 to 0.7. One thing that I have heard about exposing digital cameras is to shoot with the histogram as far to the right as possible without clipping anything. Which I can honestly say I don't fully understand yet But there are a few more articles which are helpful here and here.

Originally Posted by winterminute

4) What is EV? Is it a universal number or a relative number based on how far away you are from a correctly exposed shot? Or is this a value your camera produces that changes from camera to camera?

EV seems to be a universal number. But I'm not 100% on this one in particular.

Originally Posted by winterminute

5) When they talk about correctly exposed shots, do they mean an EV of 0?

Aside from the theory that there is no such thing as correct exposure (based on using under or overexposure in an artistic way), correct exposure is not really well defined, but it has to do with histograms and everything. It also depends a lot on what you're going for. Kind of a cop out answer, but it's true

Originally Posted by winterminute

6) HDRs confuse me When they' talking about taking multiple shots for HDRs, they talk about taking it -1/0/+1. From what I'm reading there are only 3 factors in exposure (duh, the exposure triangle), but I don't understand how I can change any of them without changing the "feel" of shot which would create problems when I merge them into a single HDR.
-- Longer exposure would create streaks
-- Larger DOF would change what was in focus vs out of focus

You would want to keep the aperture the same so that everything is still in the same focus, but change the shutter speed in increase and decrease exposure. HDR seems to work best on relatively still scenes, though clouds and stuff still seem to come out ok.

Originally Posted by winterminute

7) What's a DOF calculator? When would I use one? Is this a mathematical equation I use on site or something that a camera tells you.

Yes, it's something that's often on a website, like the ones here or here. Some cameras have the ability to do a depth of field preview, but even if your camera doesn't, you'll start getting a feel for what kind of depth of field you want with practice, and then it comes down to deciding how much of your picture you want in focus based on past experience. I'm sure there is also a mathematical formula floating around out there. But it all has to do with how much of the picture is in focus.

[baseballboy828]

The reason to overexpose as much as possible without blowing highlights is because noise is most prevalent in shadows. If you try to brighten a dark image, you'll add noise, whereas if you try to lighten an image that's overexposed but without blown highlights, you'll get a much better result.

[Nicole]

Originally Posted by baseballboy828

The reason to overexpose as much as possible without blowing highlights is because noise is most prevalent in shadows. If you try to brighten a dark image, you'll add noise, whereas if you try to lighten an image that's overexposed but without blown highlights, you'll get a much better result.

You mean darken an image? Otherwise makes sense... One of these days I'll pay attention to my histograms more.

[winterminute]

Originally Posted by Nicole

That depends on your personal preference and the scene that you're shooting. If you understand the various metering modes, you'll be able to better select which one you want to use for the given situation. But basically, what the camera is looking for is medium grey given the scene and the area that you've told it to look at. If you tell it to look at the whole scene (matrix / evaluative metering) you will get a different result than if you just have it look at one place (spot metering).

I'm not at the point where I'm changing my metering every single shot. Is there a metering mode that works best for all around shooting?

[Tiberius]

Nicole seems to have covered things quite well, but I'd like to add my own, if that's okay.

Originally Posted by winterminute

1) Does the camera do any metering when shooting in manual mode?

The camera will meter in the sense that it will give you a guide as to whether the camera thinks the image will be under or over exposed. However, it will not adjust any settings. I use a 350D (Digital Rebel XT), and it has a "match needle" display in the LCD screen and viewfinder. Basically, it looks like this:

-2..1..V..1..+2

It has a little pointer underneath which is underneath the V when the camera thinks it is properly exposed.

However, in manual mode the camera doesn't adjust any settings at all, it's completely up to you. Metering in manual mode is only to give you a guide to the proper exposure.

2) What's the best type of metering?

Depends on what you are shooting.

My camera has three kinds of metering: Evaluative, partial and center-weighted.

Evaluative metering considers the brightness of the entire image in order to get an exposure that gets as much of the picture properly exposed as possible.

Partial metering covers only the center of the viewfinder. You can use this to determine the exact exposure needed for the subject (such as a person's face), but the exposure may be off for other parts of the picture.

Center-weighted is kinda like a cross between the two. It looks at the entire picture, but it places more emphasis on the center of the image.

3) I've read that you should set your exposure -1 or +1 (I can't remember which) if you're shooting digital, any truth to this?

You should aim for the proper exposure, not slightly over or under exposed. But there's really no such thing as the "correct" exposure. The camera may say there is, but that's based on the camera assuming that 18% of the light falling on the scene is being reflected back. Certain conditions (like a beach or snow) don't behave like this, and the camera is fooled and gives a wrong exposure. So feel free to use the camera's metering as a guide, but ultimately the "right" exposure is what you think is best. it can be very different to what someone else thinks is the correct exposure, because photography is art, not science.

4) What is EV? Is it a universal number or a relative number based on how far away you are from a correctly exposed shot? Or is this a value your camera produces that changes from camera to camera?

EV stands for Exposure Value. The Wiki article explains it much better than I could.

5) When they talk about correctly exposed shots, do they mean an EV of 0?

As I said before, there's really no such thing as "correct exposure", but only what is the exposure that you feel is best for a particular shot.

6) HDRs confuse me When they' talking about taking multiple shots for HDRs, they talk about taking it -1/0/+1. From what I'm reading there are only 3 factors in exposure (duh, the exposure triangle), but I don't understand how I can change any of them without changing the "feel" of shot which would create problems when I merge them into a single HDR.
-- Longer exposure would create streaks
-- Larger DOF would change what was in focus vs out of focus

I'm not really up on HDR. I'd go with what Nicole said.

7) What's a DOF calculator? When would I use one? Is this a mathematical equation I use on site or something that a camera tells you.

Depth of Field is simply how far in front and behind the point of focus things can be while still being acceptably sharp. For example, if you take a picture of someone, you'd focus on their eyes. However, this wouldn't mean that the tip of their nose is out of focus. The point of focus is the subject's eyes, but something just in front or just behind (like the nose and ears) could still be in focus. The depth of field is changed by the aperture. A narrow aperture (high f number) has a deeper depth of field - something can be further behind or in front before becoming blurry. A wider aperture (low f number) has a shallower depth of field, so things become blurry faster as they move away from the point of focus.

As for depth of field calculators, I'd ignore them. They work, sure enough, but it's rather clumsy to sit down in the middle of a shoot and use them. It's much easier to either use the Depth of field preview button which lets you see the effect through the viewfinder, or simply take the photo and check it on the LCD display. make sure you zoom in though!

I'm at the stage where I want to learn the underlining theory and logic behind some of these settings and techniques, so feel free to hit me with the nitty gritty.

Thanks!

Have a look at the tutorials in my signature, hopefully they'll be able to help you out.

[Nicole]

Originally Posted by winterminute

I'm not at the point where I'm changing my metering every single shot. Is there a metering mode that works best for all around shooting?

If it were me, for now I'd probably stick with matrix/evaluative metering unless you're doing a lot where you want specific parts of the image to be exposed in a certain way. It gives you an overall reading of the image.

Originally Posted by Tiberius

Nicole seems to have covered things quite well, but I'd like to add my own, if that's okay.

Of course I'm definitely not the be all and end all of information (though it would be really, really handy ). Plus I think you've got some extra stuff in there that I didn't include.

[velvet4269]

I also have to wonder if needing to change the EV setting is camera-dependent, as well. I also frequently find myself shooting at a -.3 to -.7 EV, with my white balance set to daylight. Every so often, I'll need to drop it more, but I've yet to need to go + on anything.

Or maybe I'm just not playing enough

[Flippant]

i don't touch ev compensation, normally, becuase i don't know what the camera is doing to acheive it. when you shoot in full manual mode, is there any purpose to adjusting ev compensation rather than shutter/aperture? when the camera set in manual mode, and bracket mode is used, let's say +/-1EV, what does the camera do to change the exposure?

[winterminute]

Should a well-balanced histogram come very close to EV 0?