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Thread: Lens Distance Question

  1. #1
    Doughboy's Avatar
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    Bill

    Lens Distance Question

    Ok, I am about ready to go insane here as I have been searching the internet for the last 2 hours looking for the answer, and not having the luck.

    For example:

    a 500mm lens will work out to how many feet in distance.

    I just want to know how far a lens is good for, what the formula is per say.

    I hope I am making sense here.

    Any help would be great, I used to know it, but that was a while ago and I have no idea where I read it. And with google I think the problem I am having maybe is not wording ir properly.

    Thanks guys and Gals

    Bill

  2. #2
    pwnage101's Avatar
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    Troy

    Re: Lens Distance Question

    All you really need to do is some ratios/proportions. get to know your camera's sensor dimensions and draw a triangle, kind of like ken rockwell's. then just figure out the size of your subject and draw an equivalent triangle.

    For example, if the size of a sensor dimension is 1 unit and your lens is 10 units long, a distance of 50 units is needed to fill the frame with an object 5 units wide.

    edit: alright, i'll do it
    With a target composition of 1 meter on the long end, you'd need to be standing 22.5 meters away from the subject with your XTi and 500mm. 22.5 now becomes your multiplier - if you want to capture something 2 meters wide, just double it to 45. feet are overrated !
    Last edited by pwnage101; 23rd March 2010 at 06:39 AM.

  3. #3
    Doughboy's Avatar
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    Re: Lens Distance Question

    Honestly I totally blow at math, lol, but maybe i will look again when i am not as tired hehe

  4. #4
    Amberglass's Avatar
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    Re: Lens Distance Question

    Hi Bill, if you have the iphone; you can find several apps for depth of field calculations and hyper focal lengths. Or you can purchase a DOF calculator from any photography shop, for example http://www.bhphotovideo.com/bnh/cont...=REG&A=details. Online for free:http://www.dofmaster.com/dofjs.html

  5. #5

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    Re: Lens Distance Question

    Quote Originally Posted by pwnage101 View Post
    With a target composition of 1 meter on the long end, you'd need to be standing 22.5 meters away from the subject with your XTi and 500mm. 22.5 now becomes your multiplier - if you want to capture something 2 meters wide, just double it to 45. feet are overrated !
    It works with feet, too, despite the fact that they're overrated.

    As Troy said, the ratio between distance and full-frame horizontal dimension for a 1.6-crop camera and 500mm lens is 22.5. The ratio between distance and vertical dimension is about 33.5. It makes sense that the vertical number is larger, since you have to move back farther to fit the same subject into the short dimension of your sensor.

    So at 100 feet, with your camera in landscape mode, a subject 3 feet tall fills the frame top to bottom (100 / 33.5 = 3). With the 3/2 ratio of the sensor, a 4 1/2 foot subject could lie down in the frame at the same distance (100 / 22.5 = 4.5).

    And just like meters, with the same orientation, 200 feet frames 6 feet, etc. So if you think in feet, pick one of these numbers to remember, and then double out or in.

    Cheers,
    Rick

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