Quote Originally Posted by Jeff Cashdollar View Post
This is one of the main reasons I want to purchase 500MM (Its bigger)!!, to complement my 400MM (4s=8) (5s=25) (5/4) =25% increase. I guess as a general rule I will try and fill at least 30% of the frame to avoid a big-crop. Interesting, with a 1.4 TC applied to the 500 it really takes off - (4s=8) (7s=49) (7/4) =75% increase,... intuitive, 700 is almost twice 400 (400 X 1.75=700). Not to mention auto focus works as well on most Canon bodies.
Jeff,
You've got a couple math errors error here.
4 squared is 16, so going from 400mm to 500mm will yield a 56% increase (25/16=1.56)
in the area taken up in the frame by your subject. Going from 400mm to 700mm will give you
a 3x increase in subject area. Like Artie said, subject size increases with square of the focal length,
so doubling the focal length gives you a 4x increase in the area taken up by your subject in the frame.
Also, note that when increasing focal length, you also decrease the
field of view, better isolating the subject with less of the surrounding background showing in the frame.
For example, you can get the same subject size with a 300mm at 15 feet that you get with a 600mm at
30 feet, but the image created with the 600mm will show a smaller portion of the background, possibly
eliminating background distractions that may appear in the 300mm image. Also, the longer focal length
will cause the area outside your depth of field to blur faster so even though you have the same DOF,
the background may look very different. Just wanted to point out that increasing focal length does
more than just increase subject size at a given distance.



Artie,
Perfect portrait, but I'll agree with your "ugly as sin" description.
Any theory as to why TV images are big sellers, i.e. who uses them?
Did you ever make it to the water lilies .. would love to see what you
come up with!