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What focal length would I need to... (1 Viewer)

imagedude

Well-known member
allow me to fill the frame (Canon 300D) with a 12 inch high bird that is about 30 feet away?

Are there any charts that help with matching lens selection to subject size and distance?
 
imagedude said:
allow me to fill the frame (Canon 300D) with a 12 inch high bird that is about 30 feet away?

Are there any charts that help with matching lens selection to subject size and distance?

First thing is to calculate the vertical field of view required - about 1º.

Then use the Field of View Calculator on this site. And you'll find that an 800mm lens on a 1.6x crop camera (like the 300D) will give you a vertical field of view of 1.1º.

At 30 feet distance that will fill the frame with a 14" high bird.
 
Hi imagedude
This is what I do if I need to work out what lens I would need for say a ship or far off subject.
First I find out the size of the object.
Then, I find out the angle of view of the lens in degrees.
Then I change the degrees to Mils - about 17 mils to the degree.
THEN it's simple as 1 Mil subtends 1 metre in a thousand!

easy peasy!!
Mind you I've never done it for a small object but I guess it's still works.
But surely at a close distance you could set up a dummy object.
Cheers,

madmike
 
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