No. If you were getting the same field of view at a higher magnification,
then you'd be right. The amount of available light would be stretched out
more, lowering the surface brightness of things. But what you're getting
with the bigger eyepiece is increased field of view. The brightness of each
object in the field (determined by the scope's aperture) is still the same.

Think of it this way. The larger format allows you to see photons that
enter the scope at greater angles (and therefore form images further away
from the optical axis), but it doesn't change anything else.


"Dark Helmet" wrote in message
. net...
So, won't a 2" eyepiece spread the photons over a wider area and,
therefore,
appear less biright than a 1"?

Dark Helmet




"Bill Nunnelee" wrote in message
hlink.net...
Both formats use the entire objective, but the 2-inch eyepiece will
"see"
a
larger portion of the focal plane. If this sounds contradictory, keep
in
mind that photons from a celestial object are still traveling along
parallel
paths when they encounter the objective. The objective changes their
direction so they form an image at the focal plane. Photons that end up
near the edge of an eyepiece's field of view came from all regions of
the
objective, not just its edge.



"Bruce W...1" wrote in message
...
Does a 1.25" eyepiece not use as much of the objective lens as a 2"
eyepiece?

All tubes have a focal length at which there is a focused image. If a
smaller eyepiece captures less of this focal plane than a larger
eyepiece then there is loss.

I'm no lens expert but it seems that a larger eyepiece would capture
more of the focal plane. A smaller eyepiece wastes some of the focal
plane.

Is this true or does a smaller eyepiece use as much of the objective
lens as a larger eyepiece?

Thanks for your help.