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09-19-2009, 10:23 AM   #16
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QuoteOriginally posted by rustynail925 Quote
thank you very much singlespeed and marc..

what about the sides? same measurement as the front and back?
Not sure what you mean here. When I say front and back, we mean literally how far from the camera something is, and that applies whether we are talking about the sides or some other part. If DOF is 6 feet, that means there is a six-foot-deep "zone of acceptable focus" that cuts all the way across the image. So if for example you are shooting from a stage looking out at an audience, seeing all these people sitting in rows, and a six-foot-deep "zone of acceptable focus" is enough to get two rows of people in focus, then there will be two rows of people in focus *all the way across the frame*. Might not be the *same* two rows everywhere, because the people in those rows at the sides of the frame are physically further from you than the people in the center, but there will be two rows' worth of in focus people all the way across.

QuoteQuote:
and how do you know what lense that produce a nice blur background?
"Nice" is subjective. The usual term for how the out of focus areas look is "bokeh", and if you Google that term, perhaps in conjunction with different lenses, you'll see endless debate on which lens has better bokeh than which.

But *amount* of blur- or more specifically, how much of a scene will be in focus and how much will be out of focus - is what the DOF formula tells you, and is exactly the same for any lens. As the formula shows, the way you get a shallower DOF (more things out of focus) is with a wider aperture, so if you're concerned about being able to to create those effects, you get a lens with a large maximum aperture - at least f/2.8, preferably larger (and remember, smaller f-numbers mean larger apertures).

It's also the case that the focal length of the lens affects the DOF, as the formulas will show, but in kind of an indirect way, depending on whether you are thinking of shooting from the same distance with a longer focal length, or stepping further back in order to make your subject appear the same size as it did with the shorter focal length lens.

09-20-2009, 06:34 AM   #17
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thanks again marc and singlespeed for helping out
10-06-2009, 02:50 AM   #18
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Hi

Not trying to steel the thread but seems logical to proced...

About "Hyperfocal Distance Definition" in Online Depth of Field Calculator
It seems a usefull tool because "When the lens is focused on the hyperfocal distance, the depth of field extends from half the hyperfocal distance to infinity."
Meaning that we can use a lens with F4 for instance and still get a huge depth of field ?
How do we do it? ?
10-06-2009, 05:31 AM   #19
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QuoteOriginally posted by netuser Quote
Hi

Not trying to steel the thread but seems logical to proced...

About "Hyperfocal Distance Definition" in Online Depth of Field Calculator
It seems a usefull tool because "When the lens is focused on the hyperfocal distance, the depth of field extends from half the hyperfocal distance to infinity."
Meaning that we can use a lens with F4 for instance and still get a huge depth of field ?
How do we do it? ?
You have to also realize that hyperfocal distance is a function of lenses' focal length. Essentially, the longer the focal length the farther away the hyperfocal distance is going to be.

The way you can use this, is to set the camera to manual focus, turn the focus ring on the lens to about the distance needed (say 20 feet, using a 50mm lens) (rather than focusing thru the viewfinder) and that will give you a depth of field of 16 to 24 feet. To get out to infinity, set the focus to about 100 feet.

Now, lets say you have the kit lens mounted. Set the focal length to 18mm using f4, you would want to set your focus to about 14 feet.

On the same site as the DOF Calculator, there is a link to a page that produces a table, that you can print and take with you

Depth of Field Table

hope that helps...

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