telescope question?

Question

I've just got my first reflector telescope today. when I look through it, I see a black spot in the middle. can anyone tell me I am suppose to be seeing this because its blocking a third of my view.

I posted what I see on this site. I did my best to take the picture with a digital camera so sorry if the image is messed up.

http://img105.imageshack.us/my.php?image=hpim0243qa6.jpg

Answer 1

That "black spot" is actually the secondary mirror for your telescope. It has to be there. If you focus your telescope properly on the stars, you won't notice it at all.

Answer 2

The black spot is the secondary mirror. This is visible when looking down the tube from the front or down the focuser tube without an eyepiece.

Once you put an eyepiece in you won't notice it for two reasons. First of all, the secondary mirror bounces light from the primary mirror into the eyepiece. Second of all, try this...when looking at something with your telescope (and a low powered eyepiece), such as the moom, slowly move your hand in front of the opening of the telescope up front.

You will not see your hand but the view will eventually start to become dimmer. The reason is, you are focused on the moon, not your hand, and the light from the moon is actually bending around your hand somewhat. This is called diffraction. The light from what you are looking at bends around the secondary mirror obstruction to some degree when it is entering the telescope, and strikes the primary mirror in the back. The portion of the primary mirror where the shadow of the secondary mirror actually falls, is right in the middle of the primary mirror. This portion of the mirror is not used. There could be a hole in the very center and you wouldn't notice. Telescopes with folded designs have just this, and the light is reflected from the primary, to the secondary, and out the back through the hole in the primary.

Interesting no?

Answer 3

Kris is right---that's the secondary mirror and it's supposed to be there. Blocking part of the aperture is not desirable, but it is unavoidable in (most) reflecting telescope designs. You won't notice it in the properly-focused image. If you look at a star and then de-focus the telescope, the presence of the secondary blockage will become apparent because the out-of-focus image of the star will be a little donut instead of a disk. This is all perfectly normal.

Answer 4

That's a picture of your secondary mirror, mounted on a 3 vane spider. It's supposed to be there, but I'm not sure how it's blocking your view - that looks like a picture taken straight down the tube. If you look through the focuser, without an eyepiece, you should see the secondary as a circle.

Answer 5

Yes, the "central obstruction" is a necessary part of a Newtonian telescope. You are seeing what you should see - without an eyepiece. Put in an eyepiece and focus it and you won't see the obstruction.

Answer 6

well have u seen sumthing at the front it may be sumthing black dat is covering it!
check out the front stuff there may be the problem!