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TomCurious

Bay Area, US
2352 posts

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"RE: You need to be careful here Tom..."

TomCurious Registered since 03rd Jan 2007
Sat 10-Mar-12 05:00 AM

>"DX has less DOF than FX."
>
>You were doing well, until you said this Tom. In fact, one of
>the key limitations of DX is that an f2.8 lens acts like an f4
>lens on FX. You can never obtain the same shallow DOF you can
>with FX. The corollary to this is that with DX you get the
>same DOF for the same scene with an aperture one stop larger.
>
>
>This is quite consistent, however, with a crop having less DOF
>than the file from which it is cropped.
>


You may want to read the post first. For the same focal length, subject distance and f-stop, indeed DX has less DOF than FX. It will be so much simpler if you simply go to a DOF calculator like this one and try it out yourself. This will save us endless arguments in this thread:

http://www.dofmaster.com/dofjs.html

Once you've done the homework , here is the reason for why what you said is also true: An f/2.8 lens on DX will act like a f/4 lens on FX, because, in order to achieve the same framing and composition, one will either need to shoot DX at a wider angle, or get farther away from the subject. Both will increase the DOF dramatically, and more than make up for the smaller CoC (Circle of Confusion) that the DX sensor has.

Alas, this is not the scenario discussed in this thread. The topic was cropping (in camera or in post), while not changing focal length or subject distance.

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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ID
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...
9
          Reply message RE: Yes, that's right Tom...
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