A very generous soul recently donated his telescope to my work group. Actually, his wife insisted that he get rid of it since he never used it anymore, but either way I am now in possesion of a fine-looking homemade dobsonian reflector. Based my knowledge of scopes, it appears to be complete, except that it lacks an eyepiece (it has a 2 inch focus mount) or any instructions.
Unfortunately, that is one element of telescopy about which I know nothing. How do I go about finding an appropriate eyepiece for this scope? Is there a good general purpose eyepiece, or do I need one appropriate for this scopes’ focal length and diameter? Also, once its assembled, how can I tell if all of the optical elements are properly collimated?
I only have time for a quick reply, I’m sure others here will be able to fill in with more details. A good general eyepiece to start with will have a 25mm focal length. This should give you a magnification on the order of 50 to 80 times, depending on the focal length of the primary mirror. Unfortunately, the 2" O.D. eyepieces tend to be more expensive than the 1.25" variety. You should check out either or both the magazines Sky and Telescope and Astronomy to get an idea of prices, and also to look through the classifieds to see if there’s anyone in your area who’s looking to sell what you need.
As for collimating the scope, check your local library for the Amateur Telescope Makers Handbook - a classic reference chock full of great information.
Have fun with your new scope, and if you are married, make sure you introduce your partner to the joys of astronomy so that you won’t have to give it away yourself some day!
Google for “Collimating a Doson Telescope”
Scroll down the page to find several articles applicable to your inquiry.
Much more Dobsonian informations on all phase!
Careful there. A “reducer” is a lens system that reduces the focal length of a telescope. You don’t want that. What you want is a simple 2" to 1.25" adapter.
Depending on your budget and the focal length of the telescope, you might look into a 30~35mm 2" eyepiece to get the lowest power possible. (Low power is desirable for looking at faint fuzzies. Lower the power, the higher the surface brightness.) You’d want two or three eyepieces to cover a range of magnifications. Perhaps 32mm, 20mm and 7mm, or something like that. Tell us the aperture and focal length so we can give a better informed advice.
It’s a big mother: 18" primary mirror, and when it’s fully assembled the focal length (I assume that is the distance from the primary to the eyepiece) is probably in the 5 to 6 foot range. Right now its in pieces so I can’t really tell.
Very nice. In that case you’d definitely want a big 2" eyepiece to get a reasonably low power, around 35mm. I’d also get a couple of 1.25" eyepieces - 25mm and 13mm, perhaps.
I’m afraid I don’t know much about big 2" eyepieces. You might want to hang around Cloudy Nights - it has review articles and a very good message board. There’s a huge range of eyepieces available - the Orion Deepview 34mm is $60, and the Nagler 31mm is around $620.