On Mar 3, 4:48*pm, Marco Dorantes wrote:

(snip) I just bought a reflecting
telescope (snip) there
definitely is a problem because the image I see in the eyepiece is
blocked (at the center of the image) by the shape (shadow) of the
internal diagonal mirror.
Am I missing something?
Is my telescope somehow broken?
Could you please shed some light on my issue?

To provide added support to what others have already stated: You're
not missing anything other than experience with a reflecting
telescope. Your observation is *not* indicative of a broken
telescope.

Your reflecting telescope has a diagonal (often referred to as a
secondary) mirror in the middle of its optical tube assembly (OTA).
When you look *at* the eyepiece from a distance when the telescope is
pointed at any bright, daytime-illuminated object you *will* see a
bright disk of light with a smaller, dark disk in its center. This is
the telescope's "exit pupil", and this appearance is perfectly normal.

Apart from the exit pupil, when you point the telescope at the night
sky each star will take on the same appearance -- a disk of light with
a smaller, dark disk in its center -- *until the telescope's focus is
properly adjusted*. As the telescope arrives closer to a proper focus
these disks will shrink. When the telescope reaches a proper focus
the stars will take on the expected appearance of tiny, pinpoints of
light *without* dark spots in their centers.

Under most circumstances the dark central spot in the telescope's exit
pupil (when looking through the focussed telescope) will fall in the
center of your eye's pupil. The surrounding light will enter your eye
and form a more or less flawless image on your retina. The dark spot
will have no visible effect most of the time when the telescope is
used for astronomy. It's only visible effect will occur when low or
very low magnifications are used when looking at bright or daytime
objects. This is because the dark central spot increases in size as
the magnification is lowered -- *and* the eye's pupil *decreases* in
size when looking at brighter objects. At low enough magnifications,
when looking at bright enough objects the spot can block most of the
light from the eye's pupil and create an undesirable 'shadow' effect,
but under most normal circumstances, particularly when using the
telescope astronomically, this effect will be completely unnoticeable.

Bill Greer
To sketch is to see.
http://cejour.blogspot.com
http://www.rangeweb.net/~sketcher