Is there a way to mathematically figure out what focal length I need for this shot? (camera, format)

[harmonica44]

I am shooting a film project on a very low budget, and I would like to make a shot look like the camera is placed in the middle of the street, dead on.

However, I cannot afford to close the street and put the camera in the middle of it. So I thought it's probably best to shoot with a telephoto lens from the sidewalk (where I am allowed to be), and get a long enough telephoto that if I zoom in down the road enough, the POV will look like it's in the middle of the road.

But is there a way to calculate how long of a telephoto lens I would need to get in order to have that degree of angle, for the shot?

Thank you very much for any advice here!

[stephenMM]

I'm sure there is a way to calculate it, but the known parameters would be dependant on what sort of camera you're using. A 35 mm film camera would take a different focal length lens than a medium format camera. A full frame digital camera would need a different lens ratio than a 4 thirds digi camera.

You could make this much simpler by just buying a zoom lens.

[ben Shunamit]

It won't look like it's in the middle of the road. The perspective (relationship between the sizes of near objects and far objects) is a function of distance, not focal length. If you only want to get one object the right size, the mathematical function is simple: if you are twice as far from the subject as you would like to be, use twice the focal length.