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DPChallenge Forums >> Tips, Tricks, and Q&A >> Bracketing Exposures?
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 01/03/2004 05:16:03 AM · #1
I have read in many books that it is recommended to bracket the shots if the object is very light, very dark or if the light is very contrasty. Can anyone please tell me what this bracketing exposure really means? I would appreciate any help!

Thanks in advance!
 01/03/2004 05:36:24 AM · #2
Try a Google or Yahoo search! I really don't know! I SUPOSE something, but, I can't say 4 sure!:)
 01/03/2004 05:52:08 AM · #3
Hopefully this will answer your question > //www.dpreview.com/learn/Glossary/Exposure/Auto_Bracketing_01.htm
 01/03/2004 06:06:02 AM · #4
Any situation has an ideal combination of ISO, aperature (f-stop) and shutterspeed setting. The camera tries to measure the light and calculates this combination. It isn't perfect, because it uses a reference that thinks all situations average to 18% grey luminance. Faults are made for example when you photograph snow or a large crowd with dark suits on and many, many other ocassions (stuff with a lot of sky or water for example, or buildings with huge white /shiny walls or a room spotlit by a very bright window).

You use exposure bracketing to compensate for the camera's mistake. You could also do that with direct exposure compensation or a combination of bracketing and compensation.
The compensation is usually measured in EV. 1EV compensation means 1 stop of compensation and that means 1 doubling or halfing of the amount of light that hits the sensor. You can do this compensation in 1/3th EV intervals, usually to a maximum of 2EV in either direction (if you also use exposure compensation you could raise this to 2+2EV). If you use the manual setting on your camera you do this by hand and can make the maximum difference unlimited.
Exposure bracketing is a function on a camera, not all cameras have it.

So for example you shoot a bright winter landscape. The brightness fools the exposure meter, because it is brighter then its 18% reference. So the camera decides to underexpose. The result will be too dark grey snow, dark shadows and probably also a dull sky.
Here is where you either use direct exposure compensation if you know exactly what to do (in what direction to go an by how much) or rely on exosure bracketing that takes one shot in the measured exposure, one shot underexposed and one shot overexposed (in relevance to the measured exposure. You will need the overexposed shot, this one will have brighter white snow and so on.
In numbers it does this:

In shutter priority:
Measured: 1s @ F5.6
+1EV: overexpose: 2s @ F5.6
-1EV: underexpose: 1/2s @ F5.6

In aperture priority:
Measured: 1s @ F5.6
+1EV: overexpose: 1s @ F4
-1EV: underexpose: 1s @ F8

If you have set the right amount of compensation one of the three shots is usually good. This method is especially useful if you don't precisely know what a scene needs (over or underexposure) or don't know the difference between the effects of + and - compensations.
Another use for bracketing is layering and blending the over and underexposed shots to increase the dynamic range, but that's a long story.

01/03/2004 08:29:55 AM · #5
Basically, when you bracket you take (usually) three shots. One where you think the proper exposure is, and two more, one lighter, and one darker.

This technique is used more often with slide film because you can't fix your exposures as well as negative films or digital files.

I'd rather under expose a little bit to make sure I'll be able to properly finish it with Levels.
 01/03/2004 10:04:50 AM · #6
Thank you guys. That was really informative and pretty new info for me! Cheers :)
 01/03/2004 01:22:03 PM · #7
[quote=Azrifel
Another use for bracketing is layering and blending the over and underexposed shots to increase the dynamic range, but that's a long story.[/quote]

Azrifel, would you mind explaining what dynamic range is?
Thanks.
 01/03/2004 01:53:28 PM · #8
Dynamic range the degree of difference between the darkest and lightest points captured. Every film, scanner, and camera sensor has a limit on how wide a range of tones it can capture within a single set of exposure conditions.
 01/03/2004 03:08:01 PM · #9
Bracketing is also a good learning technique for beginners. It helps you learn what kind of exposures are needed for different situations. Also, bracketing can also be used in a more general term.

Other than exposures, you can also bracket for speed. For example, if you wanted light trails from cars, you can shoot several shots at a faster and lower shutter speed to make sure you have the right light trails in the picture.
 01/03/2004 06:15:00 PM · #10
....or get a camera with an in camera or "live" histogram feature. This way you can check to see if the shot has enough highlights, shadows or too much of either or.

A great feature to have when shopping for a camera.
 01/03/2004 07:06:41 PM · #11
Originally posted by GeneralE:
Dynamic range the degree of difference between the darkest and lightest points captured. Every film, scanner, and camera sensor has a limit on how wide a range of tones it can capture within a single set of exposure conditions.


Thanks GeneralE. Is this something that you would adjust with levels in PS? And how do you decide what adjustments to make, soley based on how the pictures looks?
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