"Brian Tung" wrote in message
...
Richard Jarnagin wrote:
It is my understanding that the area of the objective primarily
determines
the *amount* of light collected by a given instrument. You do not have
"more light" or "less light" available due to strictly a difference in
focal
ratio, unless you want to take into account the effects of increased
scattering along the longer focal length of the higher focal ratio
scope.
Understand that I am not questioning your assertion of the dependency of
image intensity upon focal ratio, only your implication of the
dependency of
the amount of available light (i.e. "more light" "less light").

Right--I was unclear. I do mean a higher (or lower) collected light
to image area ratio, which essentially reduces to image intensity.

I'm sure the increased scattering due to a longer focal length is
quite negligible. What would be there to scatter the light, aside
from the air?

I agree that the effect would be quite negligible, and that was my point...
there is essentially no difference in the amount of light delivered to the
focal plane by scopes of like aperture and design but of different focal
ratios. Only the image scale and the resultant intensity are affected. I
know you already know this, Brian. I just didn't want someone to become
confused by the "more light" "less light" thing.

Richard