View Full Version : test questions for beginners

07-09-2001, 01:08 PM
Struggling with basic math:

The focal length of a camera lens is the distance from the center of the lens to the point at which parallel rays of light will all be focused. For a pinhole camera, the focal length is the distance from the pinhole to the film plane. The dimensions of a frame of 35-mm film are about 24mm x 36mm. Assuming thatm the human visual system has an angle of view of 90 degrees, what focal length should be used with 35mm film to achieve a natural view?

07-09-2001, 01:51 PM
Well, im buggered if i know?

The way i would work this out is by supposing the height of the film is 24mm.
if the view is 90 degrees, then 45 above and 45 below.
But if this angle is 45, i get f=12mm????

i wish i could draw it for you.

It makes no sense to me

Rob The Bloke
07-09-2001, 03:30 PM
dunno, but heres my thoughts...

human eyes have a camera angle of 53 degrees. As for focal length, I dont know, my only other question would be that humans have two eyes, so would steroscopic vison have an impact when trying to compare it to a single view camera?

07-09-2001, 11:38 PM
Would that be 90 degrees vertical or horizontal FOV? It seems like just basic trig, you know the height of the triangle (half the film heigh or width), and two of the angles (one is half the FOV, i.e. 45 deg. and the other is 90 deg) so you should be able to get the length of the bottom side.

a / | b
/ |

Where b is the top half of the film, a is the hypotenuse and f is the focal length. The angle af is half of 90 degress beacuse this is a (inaccurate) view of the top half of the film.

[This message has been edited by harsman (edited 07-10-2001).]

Tim Stirling
07-10-2001, 12:54 AM
The full FOV for a Human is about 160 degrees, however, there is only a small section that is fully in focus- i think maybe about 35 degrees. Working out the exact FOV needed would be impossible, especialy since you are looking at a monitor and not directly into your eyes. The only solution is to find what FOV feels most natural, somewhere between 45-60 degees in for the half FOV that is usualy used with computers and the glu function.


07-10-2001, 01:51 PM
50 mm lenses are considered the "normal" length for 35 mm cameras (anything less is wide angle, anything more is telephoto).

07-10-2001, 03:37 PM
I think you should keep an artistic frame of mind when doing 'scenes', no matter what the math works out to. When you go to the movies you subconciously seek out the best seat from which it looks most 'real.' (which in most theatres is about half way back). Too close and you're not getting the big picture -- nosebleed, and you don't feel 'part' of that picture.. For special effects and accented 'movement' in the scene the math can, of course, be fudged to accentuate.. -- MikeH