About Eyepieces & Accessories
 Eyepieces
A small number of good ones is better than a large number of bad ones. You will need a low-power, wide-field eyepiece, both for finding things and for low-power views of big, diffuse objects. It might give a magnification equal to five or six times the telescope clear aperture, in inches.
The next power you will likely reach for is medium to medium high, for a good look at detail in the object in view 20 to 30 times the telescope clear aperture, in inches.
Your next choices will depend on what you like to look at. If you are not sure, hold off buying more eyepieces till you find out.
Fast Dobson-mounted Newtonians, require fancy, expensive eyepieces to give good views, because the steeply converging light cones. Slower instruments can use simpler eyepiece designs. Inexpensive telescopes like f/5 Dobinsons need expensive eyepieces, but expensive telescopes like most Refractors and Schmidt-Cassegrains, with f/8 to f/15 numbers can use cheap eyepieces.
"Zoom" eyepieces, which change focal length at the twist of a knurled ring, tend not to be very good. Barlow lenses, also called telex tenders, multiply the focal length of the telescope with which they are used: It used to be that they generally worked well only with telescopes with large f-numbers, where they were not needed -- another "Catch-22". Yet I have heard that there are now Barlow lenses that work with fast telescopes, where they are indeed needed, but I urge a try-before-you-buy approach to selecting one.
Note what high-tech eyepieces can and cannot do. The best give wider fields of view, with fewer eyepiece aberrations near the edges, than older types. The improvement is most noticeable at fast f numbers. If that's important to you, you might want some. But eyepieces are not aperture stretchers. They can neither increase image detail beyond the theoretical limit for the aperture, nor increase the number of photons that make it to the focal plane.
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Finders
What kind of finder you get depends on how you use it. If you plan on looking mostly at fine details in bright objects, then you might buy a big finder, in the hope that most of what you look at in the main telescope will be visible in it, too. This will not be applicable if you push your telescope to its faint-object limits, you would need a finder as big as the main telescope. Consider a finder that will show stars exactly as faint as those visable on your star charts. It helps a lot in identifying what you are looking at through the finder, if every star you see is charted, and vice-versa. Once the right pattern of stars is in the finder, you can put the crosshair where the object lies, even if it is too faint to see. |
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Red-Dot Non-Magnified Finders
The Telrad or Red-Dot, allows you to stare at the sky with both eyes open and see a dot, circle or crosshair of light where your telescope is pointing. A peep sight, made by taping bits of cardboard to your telescope tube, may work as well, and will be much cheaper, and any magnifying "straight-through" finder (in which you look in the direction the finder is pointing) can be used with both eyes open -- let your brain fuse the images, so you can use the finder's crosshair with the other eye. I do not use these units, personally I prefer a finder. |
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Planisphere
Preferably a plastic one that won't SOG out with dew and that may survive being sat upon. It's a fast way to find out whether a particular object is up before observing, or to determine how long it takes to wait before it is well-placed.
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Pocket Atlas
I like Sky & Telescope's Pocket Sky Atlas or the Philip's Pocket Star Atlas . |
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Table Atlas
Aa book that will lie reasonably flat, showing stars to the naked-eye limit and lots of deep-sky objects to boot, Norton's Star Atlas; there are lots of others. |
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Deep Sky Atlas
Uranometria_2000_ or the AAVSO atlas, with a stellar magnitude limit of 9 or 9.5 and a vast number of objects. |
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Planetarium Program
If you are a beginning astronomer, I do *not* suggest you rush out and buy a computer, but if you already own one, you might bear in mind that there are programs that will turn your console into a window onto the simulated heavens, with features for finding, displaying, and identifying things.
Some folks run such a program on a laptop, at the telescope. Please put red cellophane over your console. |
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Red Flashlight
You can read your charts and notes without ruining your night vision, or that of people near you. The kinds that have a red light-emitting diode (LED) instead of a flashlight bulb are particularly good. If other observers scream and throw things, your light is probably too bright.
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