# Auto Exposure Bracketing??



## MommyOf4Boys (Jun 27, 2006)

I have been reading about AE bracketing which is a capability on my camera.  I really like how it works, but I am confused about the numbers...how many stops are equivilant to each bracketing number?

My camera can be set at:
0.3 step
0.7 step
1.0 step
1.3 step
1.7 step

does anyone know what the EV stops are for these numbers?


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## Philip Weir (Jun 27, 2006)

I suppose whoever invented F/stops Knew what they were doing, but when you consider say F8 being exactly twice the exposure of F11, but numerically 8x2=16, so the numbers don't work to any numerical system that I can figure out. Now to answer your question a +0.3 step is plus 30% or approximately 1/3 of a stop wider open or should I say it gives not double the exposure, which would be +1.0 but 33.3% more exposure and the rest follow that principle.  Trust this makes some sense to you.


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## Tiberius (Jun 28, 2006)

Just a guess (I'll have to look this up), but last I checked Apertures were circular.  The area of a circle (and thus the 'volume' of light that passes through) is a function of the square of the radius.  8^2 = 64.  11^2 = 121, which is almost twice 64.  So perhaps the f stop number is proportional to the radius of the aperture opening.

Edit: http://en.wikipedia.org/wiki/F_stop would appear to support that Hypothesis.


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## Philip Weir (Jun 28, 2006)

Thanks "Tiberius" I've got no doubt you're right, it shows you an old dog can learn new trick.  Philip.


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## MommyOf4Boys (Jun 28, 2006)

where are my friendly math nerds to simplify this for me? LOL


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## markc (Jun 28, 2006)

I don't know what kind of camera you are using. You'd have to check the manual. What would make sense is that those numbers are how many stops each step is. Does it say how many shots it will take in each bracket? If it's 3, and you set it to 1.0 step, you should get one image at -1 EV, one at normal, and 1 at +1 EV. If you get 5 images and it's set to 0.3 step, then you should get -0.6, -0.3, 0, +0.3, and +0.6 EV. On my camera, you get all those shots from one press of the shutter button.


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## MommyOf4Boys (Jun 28, 2006)

I have the Nikon D50.  It takes 3 consecutive variated shots in the bracketing mode.  So if I set it to 1.7, then i should be fairly close to the 2EV steps that I want to be for blending the images?


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## Big Mike (Jun 28, 2006)

It's probably in F-stops, rather than EV measurements...but I don't know for sure.


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## markc (Jun 28, 2006)

MommyOf4Boys said:
			
		

> I have the Nikon D50.  It takes 3 consecutive variated shots in the bracketing mode.  So if I set it to 1.7, then i should be fairly close to the 2EV steps that I want to be for blending the images?


That's my guess, but I don't know the D50. You could just set it in AV mode and move the shutter speed yourself if you want exactly +/- 2 EV. (EV is just Exposure Value. You can change it by changing shutter, aperture, or ISO.) I'd keep the aperture the same so that the DOF doesn't change from image to image.


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## MommyOf4Boys (Jun 28, 2006)

thanks Mark.  I have learned about doing all of that..I was just trying to take a shortcut because I like the way the bracketing takes burst shots.  It really helps when you are trying to take shots of something quickly in different exposures, like a sunset that changes quickly.  I will just have to practice my "quick draw mcgraw" hand at changing the shutter speed manually lol!


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## fightheheathens (Jun 28, 2006)

if i remember right, the F stop is the diameter of the apeature divided by the distance from said aperature to the film plane, hence the wierd numbers.

or as wikipedia tells me...in photography and optics, the *f-number* or *focal ratio* of an optical system expresses the diameter of the entrance pupil in terms of the effective focal length of the lens.


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## MommyOf4Boys (Jun 28, 2006)

ok, that is getting way too technical and I think off base..i am just wondering what EV values those numbers are up top. 1 ev, 2 ev? etc  I know what my aperture and exposure settings are and how to correctly use them.  I think I am just going to manually do my exposures..2 EV stops under, right, and over exposed...ahhh and yes, I know exactly how to get my 2 EV stops lol.  I think to save time from using my brain or a calculator, I will carry my EV table along with me! lol


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## ksmattfish (Jul 16, 2006)

Tiberius said:
			
		

> So perhaps the f stop number is proportional to the radius of the aperture opening.



f/# = focal length divided by the actual diameter of the aperture

So with a 50mm lens, an aperture 25mm wide is f/2, while f/4 is only 12.5mm wide.


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