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Photography Forums
GadgetGal
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Date Posted:
Mar/12/2005 7:10 AM
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Is that the correct term? When I first started I met a photographer who tried to explain this to me. I have read it in several articles and books. I realize that I am at the point now I really need to understand this. Can anyone explain the relationship between shutter and aperature? I know that there are different combinations that will achieve the same affect in lighting. Anyone care to explain or refer me to a tutorial I may actually absorb? Thanks.
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Patty
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Bratt247
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Date Posted:
Mar/12/2005 1:01 PM
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GadgetGal,
Check out THIS SITE for info on the Circle of Confusion and other Depth of Field answers.
The COC definition is about 1/3 of the way down the page.
Bob S.
My Site
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Philosophy of Life: If all else fails - read the manual!
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GadgetGal
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Date Posted:
Mar/12/2005 6:28 PM
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Thank you very much, Bob. I will get over there and check it out. Take care.
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Patty
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BobF
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Date Posted:
Mar/16/2005 11:01 AM
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GG, there are a couple ways to look at the idea of CoC. One is the absolute technical definition which is pretty meaningless for most of us. The other is to look at a more practical definition. In practical terms, the CoC is the size of the circles of the points in an image that are out of focus. CoC relates to depth of field in that it's the size of these out of focus points that determines DoF. The generally accepted standard for measuring DoF is that the CoC is 1/100" or smaller on an 8x10 print viewed from normal distance (~2-4 feet). Fairly subjective, but there you go.
In terms of shutter and aperture, the two act together to give you an exposure; obviously. If you change one, you need to change the other by a similar ratio to maintain an equivalent exposure. So if your meter tells you the correct exposure is 1/250 @ f8, then you can shoot at 1/500 @ f5.6 or 1/125 @ f11 and have the same exposure. If you're shooting a moving subject the choice of shutter speed will render that movement differently, of course. If you think of your exposure in terms of light combintation, then it might make some sense. If you change one factor by 1, then you need to change the other factor by 1 in the opposite direction to have the same result. Look at it another way, you have 2 apples and 2 oranges giving you 4 pieces of fruit. You always want to have 4 pieces of fruit. So if you take away one apple, you need to add one orange to maintain the balance. If your exposure setting of 1/250 @ f8 equals, say, 10 units of light and you add a unit of light by changing your shutter speed to 1/125, then to maintain the balance you need to take away 1 unit of light by using a smaller aperture of f11. Each halving or doubling of the shutter speed is equivalent to 1 stop. Each change in the aperture by a factor of roughly 1.4 is equal to 1 stop. Now you can think of your addition and subtraction of light by changing the shutter speed and aperture in terms of stops. Reduce your shutter speed by 1 stop (by that I mean a faster shutter speed because you're reducing the amount of light) and you need to increase your aperture (smaller number = larger aperture) by 1 stop and vice versa. It doesn't always have to be in full 1 stop increments either because most modern cameras allow intermediate changes of 1/2 or 1/3 stops.
If you shoot in Aperture Priority mode, you choose the aperture value and the camera chooses the required shutter speed based on the meter reading. If you change the aperture setting, the camera will automatically adjust the shutter speed to maintain the same exposure. The opposite is true in Shutter Priority mode. You set the shutter speed and the camera sets the required aperture and changes it automatically if you change the shutter speed.
It's the choice of aperture that determines DoF.
The points of light that are reflected from your scene don't travel to the film/digital sensor plane as straight lines but rather as cones. At wider apertures, these cones of light can be wider to travel through the diaphragm which will result in larger circles for the out of focus parts of the shot and result in shallower DoF because more of those circles are going to be larger that 1/100" in an 8x10 print. With a smaller aperture, the cones of light are smaller as they move through the diaphragm, giving smaller out of focus circles and resulting in deeper DoF because fewer of the out of focus circles will be larger than the generally accepted size.
Long winded but I hope it helps.
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RF Photography
Message edited by: BobF on 03/16/2005 12:08:48
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Zhinka
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Date Posted:
Mar/17/2005 1:29 PM
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GadgetGal,
I highly recommend the book titled "Understanding Exposure" written by Bryan Peterson. It's all about the relationship b/w shutter speed and aperture plus includes amazing colour photos on every page with details on how he made the shot. Worth every penny IMHO.
Zhinka
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GadgetGal
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Date Posted:
Mar/18/2005 6:42 PM
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Bob F
Thank you for taking the time to explain coc and dof. I really appreciate it. I am going to study this very hard. Long winded is okay for me. Bob I do the same thing, I am very detailed and it takes me a bit to get it out. I appreciate your effort. If I don't get it, I will pick up the Peterson book Zinka. I feel like I am finally ready to try to grasp this. I have nipped at it from time to time but just danced around it. Actually bounced off it, it you know what I mean. I didn't get it. LOL I will be in the city tomorrow, I may see if my bookseller has this book.
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Patty
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PhotoKathy
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Date Posted:
Mar/19/2005 1:05 PM
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Zhinka, what's the ISBN number of the book? That may help us locate it easier. I'm trying to collect a few good reference books myself. Thanks!
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Canon user (50D).
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Zhinka
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Date Posted:
Mar/19/2005 5:54 PM
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Understanding Exposure
Author: Bryan Peterson
ISBN: 0-8174-3712-6 (paperback)
While I'm at it...another book of his that I own and love...
Learning to see Creatively (Revised Edition)
ISBN: 0-8174-4181-6 (paperback)
Zhinka
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GadgetGal
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Date Posted:
Mar/24/2005 7:36 PM
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Zhinka
I just received my copy of this book. I picked it up off Amazon for 16$. It is very helpful. Thank you!!!
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Patty
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