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TomCurious

Bay Area, US
2352 posts

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"RE: As I recall, Bill Claff's numbers indicate..."

TomCurious Registered since 03rd Jan 2007
Sat 10-Mar-12 04:17 AM

>
>For a given FIELD OF VIEW a cropped sensor on the same f-stop
>and focal length will have a different DOF than an FX sensor.
>
>But if it's the same distance, f-stop, focal length, the
>actual in-focus area is the same whether the light falls on
>the cropped portion of the sensor or the whole sensor. Just
>think about it in post processing -- if you crop you don't
>change DOF, you just change field of view.
>


No, if you crop, you change the DOF. This applies even to film - if you take a 35mm slide and cut out the APS frame from the center, the DOF goes down.

This concept is not well understood by many photographers, which is not surprising since it is not intuitive. You can go to an online DOF calculator to confirm it - dial in some scenario with a given f-stop, focal length and subject distance. Then change only the sensor/film frame (i.e. between FX and DX), and voila, the DOF changes. DX has less DOF than FX.

To understand what is going on, you can read up on wikipedia how DOF works. But here is a brief illustration: When you take a 35mm slide and make a print from it, say 8x12, and hang it on the wall, it will have a certain DOF. The DOF is determined from a certain viewing distance. Now cut out the center APS portion of that slide and make an 8x12 print from that. You would need to enlarge it more, so areas that just barely appeared in focus in the 35mm slide print will now appear out of focus, as tiny blur would have been enlarged more.

Tom
Bay Area Nikonian


http://www.tkphoto.me/

A general, generic topic 800 as DX crop or not [View all] , dhmiller Silver Member Donor Ribbon awarded for his support to the Fundraising Campaign 2014 , Fri 09-Mar-12 04:37 PM
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Reply message RE: 800 as DX crop or not
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Reply message RE: 800 as DX crop or not
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Reply message RE: 800 as DX crop or not
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Reply message RE: 800 as DX crop or not
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     Reply message Sure, viewfinder magnification...
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          Reply message RE: Sure, viewfinder magnification...
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               Reply message True...
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                    Reply message RE: True...
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                         Reply message Well, more or less...
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Reply message As I recall, Bill Claff's numbers indicate...
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Reply message RE: As I recall, Bill Claff's numbers indicate...
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     Reply message RE: As I recall, Bill Claff's numbers indicate...
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     Reply message No, Tom's right about that...
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     Reply message RE: As I recall, Bill Claff's numbers indicate...
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          Reply message You need to be careful here Tom...
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               Reply message RE: You need to be careful here Tom...
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                    Reply message RE: You need to be careful here Tom...
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                         Reply message Well Eric...
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     Reply message Yes, that's right Tom...
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          Reply message RE: Yes, that's right Tom...
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