Telescopes

Archive for May, 2009

I want to buy a good Telescope but I don't want to spend my college fund on it….can anyone point me to a great affordable one….? Thanks! Also one that has the remote would be the ideal one.

www.ebay.com

I have this cheap telescope that I want to manipulate to increase it's field of view/decrease magnification for an electronic eyepiece. Is there something I can do with the primary mirror? Do companies make the reverse of barlow lenses?

There are "focal reducers" that shorten the focal length of refractors. This is the opposite of the Barlow lens.
You can buy them, but they are specifically designed for particular scopes, and are expensive, probably more than what your scope costs. They come in 0.33, 0.50, and 0.63 power.
Making your own is possible. If you get two long focus objective lenses (a pair of front lenses from 7×35 binoculars) held close together, curved side almost touching curved side, that would be a good one.
You cannot use this on a mirror Telescope like a Newtonian because there is not enough space between the small diagonal mirror and focusing eyepiece to put one.
There is nothing you can do with the primary mirror to change the way it focuses light.

I'm looking online at www.telescope.com and I noticed that the 80mm telescopes are a lot more expensive then the 70mm's, is there a reason for this and if so, what? Thanks!

This is the diameter of the lens. The bigger the lens, the more light it brings in. When viewing things like stars at night, this means the more objects you will be able to see in the night sky (because some are more dim and put out less light, so you need the bigger lens to bring in enough light to see them). Perhaps an over simplification of the issues, but that's essentially the gist.

Focal length (expressed as f#) is very important too. Perhaps the telescopes you've been looking at have a better focal length too? I want to say the lower the number the better.

Something else that is harder to quantify is the quality of the lens. You can zoom the heck out of a fuzzy image, and it's still a fuzzy image. You want to go with some well know respected brand of optics.

If you are serious about viewing objects in the night sky, then you will want to get something that can correct for the earth's movement, so that while you are viewing, you don't have to keep manually correcting the angle to "stay on" an object.

Having looked into these recently, I am of the opinion that Celestron makes really good quality and is the most reasonable in price.

http://www.celestron.com/c3/home.php

Their NextStar SLT series is a good example of ones with the correction computer on it:

http://www.celestron.com/c3/category.php?CatID=8

If this is not in your price range, and you want a good quality manually adjusted telescope, their Explorascope is really good value for the money:

http://www.celestron.com/c3/product.php?ProdID=10
http://www.celestron.com/c3/product.php?ProdID=11

They have discontinued making them, however, I'm sure there are still places out there selling them. Edmund Scientific also made a similar manually aimed model (but theirs was always overpriced, IMHO, and the Celestron one has some nice features like you can mount the base on any stock standard camera tripod, etc.). For example, this place is still selling them:

http://www.telescopes.com/telescopes/reflecting-Telescopes/celestronexplorascope100.cfm