draculaz opened this issue on Sep 24, 2004 ยท 18 posts
PJF posted Fri, 24 September 2004 at 9:34 AM
Yes, sorry Drac but you've purchased a classic beginner's route into astronomy that has disappointed so many people. There ought to be a law against selling these things (figuratively speaking). Whenever you read stuff like 525x power on small telescopes, they are best avoided. That is a theoretical maximum, and will be useless when looking at the night sky. Your new scope has an objective lens (front end ;-)) of 60mm diameter, which is about two and a half inches. This is little more than the lens size on a pair of 10 x 50 binoculars, and you've only got one of them. So we're not talking about a lot of light gathering ability. With a lot of these cheap scopes, the lens quality is so poor that the outer areas are worse than useless. The manufacturers, in order to avoid allowing this to ruin the image, will place a physical 'stop down' ring inside the tube. This barrier will reduce the effective objective diameter to something like 40mm. You should check to see if there is one (look down the tube). If there's not one there, it's a good sign. The magnification power of a scope depends on its focal length and that of the eyepiece you use. This scope has a focal length of 700mm. You divide that number by the focal length of the eyepiece. So the 12.5mm eyepiece is what gives you the 56x magnification. The 20mm gives you 35x (probably the most useful magnification on this scope). To get the 525x, you have to combine the 4mm (which gives 175x by itself) with the 3x Barlow lens. That's a lot of likely low quality glass between you and the object. If you're lucky, your scope won't be too bad and you'll be able to use the 35x and 56x eyepieces for low power views of the moon and planets. It might be enough to raise a few hairs on the back of your neck, depending on your expectations. Your views of star clusters and galaxies will be disappointing, though. Forget 175x, even high quality scopes are lucky to use that power for anything beneficial, due to the usual unsteadiness of the atmosphere. Anyway, you (probably) have: An optical tube assembly (long bit ;-)) with an objective lens of 60mm diameter and 700mm focal length. This has a 'rack and pinion' focuser (in and out bit). There is probably a 'star diagonal' that should slot into the focuser, which turns the light path 90 degrees to aid viewing comfort (probably uses a cheap prism). You put your eyepieces in that, or straight into the focuser. At least three eyepieces, of 4mm, 12.5mm and 20mm focal length. Either one of those, or another eyepiece in the pack, is an 'erecting' eyepiece - this provides a 'right way up' view for looking at terrestrial objects (there is no up or down in space). A 3x Barlow lens (focal length extender). This goes into your star diagonal or focuser, and your eyepieces slot into it. Used with the 4mm eyepiece you get 525x mag; with the 12.5mm - 168x; with the 20mm - 105x. A tripod with an 'alt-azimuth' mount. This provides simple up and down movement, but won't compensate for the spin of the Earth. The higher magnification you use on astronomical objects, the quicker they will move out the field of view. Hope you get some decent views with it. BTW, you can make working telescopes in Bryce by combining lenses made of flattened spheres. Did somebody mention Bryce?