Godfrey DiGiorgi wrote:
On Nov 4, 2005, at 2:27 PM, mike wilson wrote:
Yer a cruel man, Godders. The biggest dimension that the lens has to
cover is the _diagonal_ of the frame. Bigger than either side. As
the image from the lens is circular, the overlap of the sides is
considerable.
Apart from fisheyes (which are very wide angle but do not cover the
frame) and those lenses that have a rectangular mask, which might
affect frame size, the frame size is generated by the cutout in the
shutter. As stated above, this is excessively covered by all
"normally" designed lenses.
You've misunderstood. This has nothing to do with format coverage.
The format gate is a rectangular cutout inside the film transport
rails. It does not sit against the emulsion, it stands in front of the
film by a couple of mm. As the nodal point of the lens becomes closer
to the film rails and the light path to the film 'overshoots' by a
small amount. An exaggerated picture of how this happens is seen here:
>
http://homepage.mac.com/godders/fchange.gif
The emulsion is the black line, the edges of the gate are in red. Green
lines indicate the light path from a short lens, blue lines indicate
the light path from a long lens. As you can see, light paths from short
lenses with a nodal point close to the film tend to grow the format.
Godfrey
Precisely as I had envisioned it, but the delta must be very small, no?
keith
