A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Amateur Astronomy
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Help with reflecting telescope



 
 
Thread Tools Display Modes
  #1  
Old March 4th 08, 12:48 AM posted to sci.astro.amateur
Marco Dorantes
external usenet poster
 
Posts: 1
Default Help with reflecting telescope

Hi,
I am complete newbie to telescopes, I just bought a reflecting
telescope (Astro-Nova 100 Telescope 300x) by Edu Science at Toy'r'us
shop.
I have done a very careful handling and setup, nevertheless, 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?

Thank you very much in advance for any help.
  #2  
Old March 4th 08, 03:31 AM posted to sci.astro.amateur
Curtis Croulet
external usenet poster
 
Posts: 337
Default Help with reflecting telescope

I have done a very careful handling and setup, nevertheless, 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?


You should only see this effect during the day. If you look at night, the
shadow of the secondary will disappear. To put you at ease: no, you haven't
done anything wrong, and this is not a defect of the scope.
--
Curtis Croulet
Temecula, California
33°27'59"N, 117°05'53"W


  #3  
Old March 4th 08, 03:38 AM posted to sci.astro.amateur
lal_truckee
external usenet poster
 
Posts: 409
Default Help with reflecting telescope

Curtis Croulet wrote:
I have done a very careful handling and setup, nevertheless, 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?


You should only see this effect during the day. If you look at night, the
shadow of the secondary will disappear. To put you at ease: no, you haven't
done anything wrong, and this is not a defect of the scope.


The original poster may be wondering how that could be.

For him: it has to do with the size of your pupils - small in daylight,
large in the dark.
  #4  
Old March 4th 08, 06:27 AM posted to sci.astro.amateur
alp
external usenet poster
 
Posts: 6
Default Help with reflecting telescope

Marco Dorantes wrote:

Hi,
I am complete newbie to telescopes, I just bought a reflecting
telescope (Astro-Nova 100 Telescope 300x) by Edu Science at Toy'r'us
shop.
I have done a very careful handling and setup, nevertheless, 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?

Thank you very much in advance for any help.


Perhaps you are not using an eyepiece in the telescope. I will assume you
have a newtonian reflector (cold be wrong). small inch or 2 inch (ok,
0.96x", 1.25" or 2" for the purists). If you have no eyepiece then the
scope will be useless. Make sure you have an eyepiece.

Second thing that could be wrong is that you are looking at a star and the
focus is way off. Out of focus stars look like fuzzy donuts.

Somehow I suspect the first scenario.


  #5  
Old March 4th 08, 04:24 PM posted to sci.astro.amateur
Jax[_2_]
external usenet poster
 
Posts: 133
Default Help with reflecting telescope

lal_truckee wrote:
Curtis Croulet wrote:
I have done a very careful handling and setup, nevertheless, 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?


You should only see this effect during the day. If you look at night,
the shadow of the secondary will disappear. To put you at ease: no,
you haven't done anything wrong, and this is not a defect of the scope.


The original poster may be wondering how that could be.

For him: it has to do with the size of your pupils - small in daylight,
large in the dark.


looking at a bright moon may show the secondary mirror for the same
reason given for daylight. Not a defect.
  #6  
Old March 5th 08, 05:11 AM posted to sci.astro.amateur
[email protected]
external usenet poster
 
Posts: 185
Default Help with reflecting telescope

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
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Please Need Help about 114mm Reflecting telescope duke Amateur Astronomy 5 July 26th 06 01:17 AM
A reflecting film for heating planets OlegMGoryunov Solar 1 January 14th 06 11:37 AM
non-reflecting coating Jimcat Amateur Astronomy 1 November 29th 04 04:38 AM
Help collimating a "classic" Tasco 11T-R 4.5" reflecting telescope Fu Manchu Amateur Astronomy 6 August 12th 04 11:44 PM
reflecting sunlight onto the Moon? Joe Strout Policy 69 May 21st 04 10:23 PM


All times are GMT +1. The time now is 01:34 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.