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09-17-2009, 03:53 AM   #1
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calculating the depth of field

i came into a site about depth of field calculator and i really dont have any clue about what it mean by this:

Subject distance 10 ft
Depth of field
Near limit 7.6 ft
Far limit 14.6 ft
Total 7.04 ft
In front of subject 2.4 ft (34%)
Behind subject 4.63 ft (66%)
Hyperfocal distance 31.2 ft
Circle of confusion 0.02 mm

is this important for a newbie to know? if it is can anybody help me out? heres the site:
Online Depth of Field Calculator

09-17-2009, 07:39 AM   #2
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So, here's the part you probably can make use of...

Subject distance - the distance that lens is focused at. If, say, you have paper target at 10ft, it will be sharp.
Near limit and far limit are limits between which the subjects will be sharp. If, say, you have two cans at 8ft and 13ft each, they both will be sharp. But, any objects out of the limit will be out of focus. So, if you have something at, say, 6ft or 16ft, that will be blurred.

The total they say is just the difference between far limit and near limit.

2.4 ft in front of subject means that everything that's within 2.4ft in front of the subject, will be in focus. Same for behind subject.

Hyperfocal distance is irrelevant in this situation. Circle of confusion is used when calculating all those distances, but you have that calculator, so you don't really have to know what that means (if I'm not mistaken, it's radius of the smallest dot that will be discernible)
09-17-2009, 09:02 AM   #3
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Also keep in mind...

that this is without regard to the quality of the lens that you're are using. Good explanation from pbo on the info that these calculators generate.

These calculators are simply looking at the physics (optics) based on focal length, aperature, and distance (from the back of the lens to the film plane & to your subject). So, your results may vary dependending on the quality of the lens.
09-17-2009, 10:12 AM   #4
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thanks for the explanation pbo, i think i have an idea of what you mean just correct me if i'm wrong here

so in order to isolate the subject from the background there are 3 things that i can adjust with. what i will do is increase the focal length , lower f/stop or increase aperture, and move near the subject ... and if i want all in focus i'll do the oppositte.

09-17-2009, 10:19 AM   #5
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QuoteOriginally posted by singlespeed Quote
These calculators are simply looking at the physics (optics) based on focal length, aperature, and distance (from the back of the lens to the film plane & to your subject). So, your results may vary dependending on the quality of the lens.
you mean lense basing on the f/stop?
09-17-2009, 10:31 AM   #6
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QuoteQuote:
so in order to isolate the subject from the background there are 3 things that i can adjust with. what i will do is increase the focal length , lower f/stop or increase aperture, and move near the subject ... and if i want all in focus i'll do the oppositte.
That sounds right! Lower f-stop and increase aperture means same thing.
09-17-2009, 10:33 AM   #7
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QuoteQuote:
you mean lense basing on the f/stop?
Calculations are based on lens focal length, and circle of confusion of the sensor. The rest are parameters that can change (like, subject distance and current aperture).
09-17-2009, 10:38 AM   #8
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Oh, by the way, the range between near and far limits is called depth of field.

09-17-2009, 11:53 PM   #9
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thanks for helping out.

QuoteOriginally posted by pbo Quote
Calculations are based on lens focal length, and circle of confusion of the sensor.
sorry i dont know this term (circle of confusion of the sensor)
09-17-2009, 11:59 PM   #10
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depth of field is use for
1. to blur background and focus the subject
2. all in focus in the picture

is there any other situation aside from what i mentioned the DOF is being use for?
09-18-2009, 05:48 AM   #11
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QuoteOriginally posted by rustynail925 Quote
you mean lense basing on the f/stop?
The calculation is based on a "perfect" lens - since no lens is perfect, your mileage may vary.
09-18-2009, 05:53 AM   #12
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QuoteOriginally posted by rustynail925 Quote
sorry i dont know this term (circle of confusion of the sensor)
If the lens was perfect, a dot (that is your subject) would focus to a dot on the film plane. Due to aberations in the lens, this dot will actually end up as a circle at the film plane. Smaller circle (of confusion) equals better resolution, or sharpness, or focus.
09-18-2009, 08:21 AM   #13
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QuoteOriginally posted by rustynail925 Quote
depth of field is use for
1. to blur background and focus the subject
2. all in focus in the picture

is there any other situation aside from what i mentioned the DOF is being use for?
Well, that's the basic idea of DOF - it measures how much of the scene is in focus, front to back. What you do with that is up to you really - you might decide you want only *part* of your subject in focus, or the entire subject and a small part of the background, or the entire subject and a large part of the background, or the subject and the foreground but none of the background, etc. Or you might have two subjects and you want to create enough DOF to get both of them in focus. Lots of possibilities for how you use it, but it means one thing and one thing only - how much of the scene is in focus.
09-19-2009, 04:52 AM   #14
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thank you very much singlespeed and marc..

what about the sides? same measurement as the front and back? and how do you know what lense that produce a nice blur background?
09-19-2009, 06:22 AM   #15
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QuoteOriginally posted by rustynail925 Quote
what about the sides? same measurement as the front and back?
Not sure what you mean by this. The Field Of View (FOV) is determined by the focal length - for a Full Frame (FF) 35mm camera, 28mm produces a wide FOV while 50mm is "normal" and 135mm would be telephoto or narrow.

QuoteOriginally posted by rustynail925 Quote
and how do you know what lense that produce a nice blur background?
Bokeh is subjective and I'm sure it's discussed in the Lens Review section as well as a ton of other threads. Some lenses are better than others and it's a matter of personal preference. see Bokeh - Wikipedia, the free encyclopedia
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