Allbest's DOF - Why does displayed subject distance varies when zooming ? - Hello, I'm a NEWBIE - HELP!! (Newbies assistance, User Guides and thank you notes) - CHDK Forum  
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Allbest's DOF - Why does displayed subject distance varies when zooming ?

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Offline Chris710

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Allbest's DOF - Why does displayed subject distance varies when zooming ?
« on: 24 / June / 2008, 10:58:41 »
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Could some one explain me why without moving the camera and focusing a same object, the subject distance displayed by the DOF calculator in miscellaneous values changes when zooming? (I mean for a fixed distance between the camera and the subject the SD value displayed won't be the same at wide angle (35mm) and at tele (210mm).) Thanks.
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Offline fudgey

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Re: Allbest's DOF - Why does displayed subject distance varies when zooming ?
« Reply #1 on: 24 / June / 2008, 12:27:13 »
Probably because the hyperfocal distance changes and along with it the subject distance approximation changes.
http://en.wikipedia.org/wiki/Depth_of_field. Also, the camera will usually not focus to the same exact distance twice in a row.
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