| Follow up to this: Many telescopes come with one or two eyepieces, and you may want to get a few more in various focal lengths. Generally, the tradeoff is long focal length: everything is small and bright, short focal length: every thing is small and dim. So, generally you start out with a long focal length to find the thing you're looking for, and switch to short when you find it and want a closer look (assuming it's something small and bright like a planet). There are also barlow lenses, which are sort of an adapter with lenses that increases the magnification of whatever eyepiece you're using. They're occasionally useful. Most mid-range telescopes have standardized on 1-1/4" diameter. Cheap/older telescopes sometimes use 0.96" and big telescopes sometimes go with 2". Adapters are available to mount DSLR camera bodies to the telescope without using any lenses at all, which is a great way to go on a Dobsonian because there aren't any lenses at all in the whole optical path to introduce chromatic aberration, only mirrors. (I don't have a DSLR camera, but in the past I've had a bit of fun taking the lenses off of old USB webcams and adhering them to the focusser shaft with poster putty. I was able to get some decent low-resolution footage of an extreme-close-up of the moon that way.) Another thing that might be useful sometimes is something you can use to cover most of the telescope aperture, for cases where you want maximum image clarity and are willing to sacrifice light-gathering. That can be handy for looking at the moon. I haven't tried using filters, but those can also be used to bring out contrast in certain things. |