At 00:09 11/24/02, you wrote:
Quiz:
What focal length is effectively half-way between 100mm and
200mm?
AG-Schnozz
Half-way in what manner? Depth of field for same focus distance? Change
in absolute aperture diameter for same f-number? Linear dimensions (height
and width) of field of view for same focus distance?
[Q: What is the air speed velocity of an unladen swallow? A: African or
European?]
I will dangerously presume you are asking about field of view at same
distance from front lens node to subject:
In that case it's simple geometry/trigonometry and the answer is
150mm. Horizontal and vertical angles of view, and therefore their linear
height and width dimensions at a given front-lens-node -> subject-distance
and specific film size are inversely proportional to the focal length. In
other words, if you fill the frame with a 8 foot wide subject at 100mm and
want to fill it with a 4 foot wide subject at the same distance, then
double the focal length to 200mm. To fill it with a 6 foot wide subject
then use 150mm focal length.
-- John
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|