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01-11-2007, 08:19 PM   #1
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Cropping by mm

I took some photos with my 43mm lens that need to be taken with a longer lens. I plan on returning to the same location this weekend and have been trying to figure out what the best focal length would be best to use. There must be a way to put a photo from a 43 mm lens in photoshop and crop it to a certain percentage so I can see what that scene would look like if shot with a 135mm lens, or any other lens.

I know I am not making myself clear. Hope one of you understands what I am trying to do.

Thanks for any ideas you could give me.

01-11-2007, 09:05 PM   #2
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u would need to crop an then enlarge.. possible but i am not sure on how to arrive at the exact size factor thow.. the enlarge is easy but getting the crop right might be awkward..

trog
01-11-2007, 09:09 PM   #3
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Trigonometry and the camera to subject distance. You can use a right triangle and approximate to a fair degree of accuracy OR use half the width/height, 1/2 the angle of view and that same right triangle for a precise answer.
01-11-2007, 11:10 PM   #4
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How about ... 43/FL (FL = focal length of other lens) X # of pixels in width of original shot. Then crop out from center 1/2 of that number each direction. Enlarge FL/43 to get back to original display size.

I have no clue what the PS commands are for that:-)

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