In article <33141A77.2A86@ra.msstate.edu>, sgr1@ra.msstate.edu says...

>How long of a lens would be required to "fill the frame" of a 35mm
>camera when taking a picture of a subject 4 foot tall from a distance of
>600 feet? Is there a simple formula for this? Thanks for any info.

Lessee...., 5400mm!
Simple proportions: 4' is approximately = 25 x 48" = 1200mm; 1200mm
subject is to be reduced to 36mm long film frame, so 1200/36 = 33 1/3;
600' is approximately equal to 25 x 12 x 600 = 180000mm; 180000/33.333
= 5400mm (one VERY long lens!). Since 1000mm's are practically nearly
useless (air currents, dust, and all that...), I would expect a very
poor image from even the best 5400mm lens, except maybe on the very
best viewing days (and I would expect that 5400mm lens to be mighty
slow, raising other problems... - perhaps moving to within 100' and
using a high-quality 1000mm lens would work better....).
(BTW, the above calculation can be done more simply: 4/600 = 36/X,
so 21600 = 4X, X = 5400mm... [gee, I guess one CAN remember grade-school
stuff! ;-].)
Hope This Helps