Understanding Exposure

[Tiberius]

Originally Posted by 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?

There is no exposure compensation setting in manual mode.

In S or A modes, you can set the aperture or shutter speed (and neither in the case of P mode). The camera then calculates the setting you didn't provide in order to provide what the camera thinks is the proper exposure. Adjusting the exposure compensation in A mode changes the shutter speed the camera chooses, while adjusting Exposure compensation in S mode changes the aperture the camera decides on. However, in Manual mode, the camera doesn't choose any settings, so there are no automatic settings that Exposure compensation can adjust.

Exposure bracketing in A mode will adjust the exposure by altering the shutter speed (because the camera figures you want a certain depth of field), and in S mode by altering the aperture. In Canon's, P mode bracketing is adjusted by shutter speed I think, but double check your camera's manual to be sure. On my Canon dSLR, bracketting in manual mode is done by varying the shutter speed. Again, check your own camera's manual, as it could be different for different companies.

Originally Posted by winterminute

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

There's actually no such thing as a well balanced histogram. As I said earlier, the correct exposure is the one that the Photographer feels is best for the particular shot. After all, a shot of a person at night is going to have a much lower brightness than a picture of a person in the desert during the day. Generally, try to avoid having large spikes on the far edges of the historgram, because they are indicative of "clipping". Spikes at the far left indicate areas of solid black, and spikes on the far right show solid white. In both of these areas, there is little to no detail at all. The best general advice is to use the highest exposure that DOESN'T provide clipped highlights (these often flash in the LCD review). This way, you have as much detail as possible and avoid shadows, because as baseballboy828 pointed out, you can darken an overly bright area without too much trouble, but brightening a dark area often introduces noise.

[Flippant]

thanks tiberius, that cleared it up for me. i was thinking maybe the camera was doing some voodoo with the sensor but i can see this was wrong. now where did i put my manual?

[winterminute]

Originally Posted by Tiberius

There's actually no such thing as a well balanced histogram. As I said earlier, the correct exposure is the one that the Photographer feels is best for the particular shot. After all, a shot of a person at night is going to have a much lower brightness than a picture of a person in the desert during the day. Generally, try to avoid having large spikes on the far edges of the historgram, because they are indicative of "clipping". Spikes at the far left indicate areas of solid black, and spikes on the far right show solid white. In both of these areas, there is little to no detail at all. The best general advice is to use the highest exposure that DOESN'T provide clipped highlights (these often flash in the LCD review). This way, you have as much detail as possible and avoid shadows, because as baseballboy828 pointed out, you can darken an overly bright area without too much trouble, but brightening a dark area often introduces noise.

Can the same be said for the EV? If that's the case, then why do people care what the EV is?

[inkista]

I think you're confused about what an EV is. EV (exposure value) is just "a stop", and means more or less light, irregardless of whether it comes from the aperture or the shutter speed.

It's a fast, shorthand easier way to deal with nudging an exposure up or down, without actually worrying about aperture & shutter settings. That's why it shows up when you're using a more automatic mode, but not in Manual mode (Manual Mode, you're just worried about the shutter speed or the aperture).

EV is mostly use as a relative value of adjustment, not an absolute one of the whole exposure. 0EV just means you're not adjusting the exposure from your current settings. +1EV means you want to one more stop's worth of light over your current settings. -1EV means you want one stop less of light over your current settings. How the EV is added/reduced depends on what mode you're in--in aperture priority, the shutter speed is adjusted, in shutter-priority, the aperture is adjusted.

[winterminute]

Ahh, I think that's why it is confusing me. For people shooting in manual, is just a data point - more informative than anything else. And in light of what Tiberius said, the EV reading isn't all that helpful since only the photographer knows exactly how he wants the shot to look.

And in the case of the people like me who can't remember what the whole stops are vs the partial stops, it helps us know how much to change the Shutter/Aperature.

Or am I still way off

[inkista]

Nope, that's pretty much it. As you say, in Manual mode, where the camera's metering says that exposure lies is just more information to use. Adjusting to 0EV just means you're doing what the camera would have done automatically. Whether it's the right exposure for your scene or what you want to get out of it is another matter.

[Tiberius]

Originally Posted by winterminute

Can the same be said for the EV? If that's the case, then why do people care what the EV is?

When you take a photo in anything but Manual mode, the camera is going to adjust certain settings to ensure the brightness of the photo is what the camera thinks is correct (based on the scene reflecting about 18% of the light that is falling on it). However, as I said before, the camera figures this out by running algorithms during the metering process, and it can be fooled by dark subjects or bright subjects. EV is a way of altering the exposure that the camera sets. You can use EV to make it darker or lighter, because changing the EV setting alters the overall exposure that the camera calculates.

For example, if you dial in an EV setting of -0.3, the result will be a third of a stop darker than what the camera would normally give you. Dialling in -0.7 will give two thirds of a stop darker, and dialling in -1.0 will give a full stop darker. Likewise, dialling in a positive value will give the image a higher exposure, making it brighter.

An example of how you'd use this...

You go for a holiday to the snow and take a picture. When you look at the view, the snow is dazzlingly white. You take a photo, but you're disappointed because the snow comes out looking grey. This is because the camera expects the snow to be reflecting only 18% of the light that is falling on it, but it is actually reflecting a whole lot more. So, the camera turns down the exposure because it thinks the image is over-exposed. However, this leaves the snow looking the colour of concrete. So, turn the EV value up a stop, and it will increase the exposure, making the picture brighter and the snow look white - exactly the way it's meant to.

So EV is just a way of giving you control over how bright the camera thinks the photo should be.

There's no EV in manual mode, however. This is because EV adjustments are designed to alter the settings that the camera calculates. However, in manual mode, there are no camera-calculated settings, so EV adjustments are handled by the photographer, not the camera.

Originally Posted by winterminute

Ahh, I think that's why it is confusing me. For people shooting in manual, is just a data point - more informative than anything else. And in light of what Tiberius said, the EV reading isn't all that helpful since only the photographer knows exactly how he wants the shot to look.

I wouldn't say that the metering indicator is useless, even in manual mode. It provides a basis from which to base your metering choice off. For example, just a few days ago I took a photo of some objects on a table under a lamp at night. I knew that the camera would expose it slightly brighter than i'd want for that picture (I wanted it to look warm and cosy), so I shot in manual mode and set my shutter and aperture so it was underexposed by two thirds of a stop. Exposure was perfect, first time. But it was only looking at the metering indicator that I was able to get it right. The exposure indicator is a valuable tool to use to let you determine what exposure to set, whatever mode you are shooting in.

[winterminute]

Originally Posted by Tiberius

You go for a holiday to the snow and take a picture. When you look at the view, the snow is dazzlingly white. You take a photo, but you're disappointed because the snow comes out looking grey. This is because the camera expects the snow to be reflecting only 18% of the light that is falling on it, but it is actually reflecting a whole lot more. So, the camera turns down the exposure because it thinks the image is over-exposed. However, this leaves the snow looking the colour of concrete. So, turn the EV value up a stop, and it will increase the exposure, making the picture brighter and the snow look white - exactly the way it's meant to.

Would this still happen if I did a custom white balance using the snow as my WHITE and an EV0? Many cameras has a scene mode for SNOW, I assume that one of the things it does it is exactly what you just described, correct?

[Tiberius]

Originally Posted by winterminute

Would this still happen if I did a custom white balance using the snow as my WHITE and an EV0? Many cameras has a scene mode for SNOW, I assume that one of the things it does it is exactly what you just described, correct?

Yes, it would still happen. White balance controls the tint of the image (different light sources create different coloured lights - lightbulbs are often orange, sunlight is white and shade can be blue), but it doesn't control the brightness of the image. Creating a white balance for snow will only ensure that the snow doesn't have a colour cast.

I suggest that you do create a white balance for snow (to stop it getting a colour cast), but you'll still need to adjust your exposure to create bright looking snow.

[winterminute]

Sounds good - You've been very helpful -- Thanks for all your replies.