Telescope help

[johnjohn320]

I found my sister's old telescope in the basement, my friend and I have decided to dust it off and take it for a spin. Other than one little screw that holds the lens steadier, everything still appears to be there. However, we can't seem to get a good shot of the moon, and I remember when my sister using it seeing some VERY clear images of the moon, so I know the telescope's capable of it. But right now, at the most focused, we can see a hell of a lot of white with some darkish dashes.

Anywho, we'll start with a dumb question. There's a 5 mm, 10 mm, and 15 mm lens. Which of these is them most powerful? (Does 15 zoom more than 5 or vice-versa?) In addition, there are 2 long tubes, one labeled "2x Barlow Lens" and the other "1.5x Erector Lens." What in the heck are these for?

Yes, we're telescope-retarded. Neither of us have any experience with this stuff. Little help for some n00bs?

 

[nativesunshine]

can't help you..but since it's somewhat on topic..

i looked at mars last night!!! And I saw the craters on the moon. Telescopes are fun!!! 😀

 

[Hayabusa Rider]

First, is it a telescope that has a mirror, or does it have a lens in front or both? About how large is the mirror/lens? When you say old, how old? Where exactly is this screw?


As far as the 5, 10 and 15 mm lenses go, they are called eyepieces.

Each telescope has a "focal length", that is how long the light path is between the lens or mirror and where the image focuses, usually at the eyepiece.

How this works...

Take the focal length (which should be marked somewhere on the scope) and divide by the mm's of the eyepiece to get the magnification.
Example- Assume a 1000mm focal length. If you were to us the 5 mm eyepiece, you would get 1000/5 = 200 times magnification. Likewise the others give 100 and 67 times magnification.

You want to use the lowest magnification that works, because a given lens or mirror fails to show more detail beyond a certain point. You reach the limit of resolution, just as if you were to enlarge a 640x480 image to huge size.
You also magnify the distortion caused by moving air/atmospheric temperature differences etc.


The barlow lens doubles the magnification, making the 10 mm work like the 5. They are usually cheaply made and in any event add some distortion to the image. I never use them.

Lastly, if you were to look at a terrestrial object through the telescope, you would find the image upside down and reversed left to right. The erector lens corrects this, and acts as a Barlow lens by increasing the magnification of a given eyepiece by 1.5 times. They also suck. When you look at a celestial object, who cares if it is inverted or not? Using one though adds extra optical defects and cuts down on the light absorbed. Not a good thing.