In article <01bc91a2$8b64cda0$9a1393cf@newmicronpc>, tonypierson@worldnet.att.net says...

>If you have a fast lens, say 1.4 set at F4 is the DOF the same as with a F4
>lens at F4? Is this variable? Isn't a lens with better glass that allows
>more light going to have slighty more DOF than a poor quality lens, all
>other things being equal?

Hmmm..., contrary to what others have posted, I will present a different
view...;-) While in theory what the other posters have said is true
(that two different-speed 50's will have the same DOF under the same
shooting conditions [among other things said]), there are exceptions
that are not uncommon. Since DOF is a perceptual thing, differences
in the optical qualities of the lenses can affect the appearance of
the DOF range. A softer lens can appear to have greater DOF, since the
area of sharp focus is less obvious. A lens with considerable field
curvature can appear to have different DOF, depending on how well
the curvature conforms with the subject shape. A lens with an incorrect
diaphragm opening for the stop marked can look different in DOF at
that stop. A lens that produces a very contrasty and "busy" out of
focus image can appear to have different DOF from one that produces
a smoother out of focus image. Maybe there are also other causes for
differences between lenses in DOF...
Hope This Helps
(David Ruether - http://www.fcinet.com/ruether )