light-weight long lenses for 8x10greenspun.com : LUSENET : Large format photography : One Thread
Does anyone know if lenses have ever been made with focal lengths in excess of 600mm (24") with a maximum apeture less than 2" or so? Most modern lenses in the range of 30-35" are F/9-12, which makes them too heavy for field work.
-- Jack Straton (email@example.com), February 13, 1998
When you recall that the f number of a lens is the ratio between its diameter and its focal length, you begin to see why a 16" f/4.5 lens would have to be considerably bigger, heavier and bulkier than a f/4.5 8" lens.
For the first case, 4.5 diameters would have to fit in 16". For the second, 4.5 diameters would have to fit in 8". Much smaller piece of glass.
This doesnt even start to touch on the correction needed for such a big glass.
-- Tony Brent (firstname.lastname@example.org), September 08, 1998.
Tony: interesting answer, but Jack wants a small lens, not a large one. An aperture less than 2" on a 24" lens means an aperture smaller than f/12. I'm afraid it looks as if no-one knows. Perhaps the answer, as with so much of LF, is "hire a pack mule".
-- Alan Gibson (email@example.com), September 08, 1998.