Now what?

You have bought your first real telescope or got one as a gift. Now you consider accessories. What do you really need?

Firstly, you will need a map to find what is out there at any given time. Atlases seem to come in three varieties: big, pocket-sized, and inadequate. Big atlases like Wil Tirion's Sky Atlas 2000 are very detailed and have large scale maps that show big sections of sky. Pocket-sized guides like the Audubon Field Guide to the Night Sky are portable and best serve as reminders of what is up when in the field. They have small, constellation-specific maps that show only bright stars. Often, they also have descriptions of objects in each constellation. I try to avoid the ones with superfluous information like astronomical history or color surface photos of planets since that kind of information is not useful in the field. Inadequate books have a lot of information that you already know, are heavy on the art work, are physically big but contain only bare outlines of what is visible at any given time.

To read your map at night, you will need a red flashlight. Angle-head army flashlights come with colored filters, including red, and are indestructible. Also, many vendors offer red LED lamps that hardly ever need batteries. Any flashlight can be made red with multiple layers of tail-light repair tape.

Next, you need a workable finder. Many commercial telescopes come with a 6x30 finder scope with no focusing mechanism. I guess they work, but most observers agree that 6x30 finders are just for decoration. Far more useful is the reflex or unit finder (so called because it has 1x magnification.) These finders appear to project a red dot onto the sky. They are very easy to use. While all unit finders are superior to 6x30 finder scopes, the best project a pattern of concentric circles instead of a dot. These include the Telrad and the Rigel Quick Finder (each is less than $50.) For those who prefer traditional finder scopes, the consensus seems to be that 50mm is the minimum useful aperture. (I have seen 90mm short refractors and even 5" SCTs used as finders for big Dobs.)

What about eyepieces? Chances are that you got a couple of brand-X Plössls or some modified achromat dinosaur with your scope. Eventually, you will want to augment or even replace them. (Keep the old ones for public star parties.) You should have at least two good eyepieces. The first is your wide-field DSO ocular. This eyepiece should give you around 5 or 6mm of "exit pupil." (exit pupil = eyepiece focal length / telescope focal ratio) This will give a wide view without brightening the background sky too much. A good choice is a Plössl, usually around 32mm. (I do not recommend a 40mm Pl. in 1.25" format because the apparent field of view is restricted by the 1.25" barrel giving a true field similar to a 32, but with a brighter background.) Plössls are a four-element design (5 for modified Plössls like Ultrascopics/Ultimas). They are well corrected down to about f/5 and generally have a respectable 50 deg. apparent field of view (that is the size of the window you look through). Typically, eye relief is around 80 percent of its focal length. Consequently, it gets a bit tight around 12mm. There are many respectable Plössls available including inexpensive models from Orion and Adorama. TeleVue Plössls cost twice as much and produce slightly better results. In five years you will not miss the extra fifty bucks, so I recommend getting a TV Plössl since you will invariably be using your scope at its theoretical limit. Meade 4000 and Ultima/Ultrascopics also are highly regarded.

Your other eyepiece should be a high-power unit for planets, globular clusters and planetary nebula. Your highest theoretical magnification is 50x per inch of aperture. As a practical matter, the local atmosphere usually limits useful magnification to around 200x if seeing is good, or 100x if the air is unstable. Plössls again are a good choice due to their good contrast and lack of ghost images. Some people feel that orthoscopics (available from U.O.) offer the highest contrast and sharpest images of planets and lunar detail. Orthos are also four element oculars, but their lenses are arranged differently than Plössls. Eye relief on orthos is slightly longer than Plössls of the same focal length, but their apparent field of view is only about 43 degrees. Both designs have similar limits in performance. At lengths shorter than around 12mm, eye relief is very tight, too tight for people who use eyeglasses while observing. Also, the limited apparent fields of view (compared to more expensive designs) make it difficult to track objects at high magnification using an altazimuth or Dobsonian mount, though it is not a problem for EQ mounted scopes. To get high magnification without losing eye relief, consider a Barlow (telenegative) lens. A Barlow increases the magnification (often by 2x) of any eyepiece while preserving the original eye relief. To minimize aberrations caused by Barlow lenses, get a good quality model such as the Celestron Ultima (a.k.a. Orion Shorty Plus) or TeleVue models.

If you can afford to drop a few hundred bucks on an eyepiece, I recommend the TV 22mm Panoptic for the 1.25" format (a new 24mm is now available) for wide-angle viewing. They have long eye relief, a 68 degree apparent field of view, excellent sharpness and contrast. With the 22mm model, the true field will be similar to a 32 Plössl, but will appear larger and have better sharpness and contrast. For 2" focusers, consider the 27 or 32mm Panoptic or the U.O. Konig MK 70. For planets and other high magnification objects, $260 will get you a TV Radian. Radians have 60 deg. apparent fields of view with contrast and sharpness similar to an orthoscopic. All Radian focal lengths have 20mm of eye relief, so very short sizes will be comfortable to use.

Refractor and Cassegrain users can often immediately improve performance by upgrading the diagonal. Many commercial scopes come with generic prism diagonals. Some even come only with 45 deg. daylight diagonals. Upgrading to a quality unit such as those from TeleVue or Astro-Physics (or even a mirror model from Orion) will allow you to significantly improve performance. Also, refractors with a lot of false color can benefit from "minus violet" filters (Sirius Optics).

Speaking of filters, in today's light polluted sky, nebula filters are extremely useful. These filters suppress background glow by rejecting some wavelengths of light in favor of those emitted by nebula. They exist in several varieties. Unfortunately, the best supplier of these filters, Lumicon, has gone out of business. Consequently, users will need to look to other vendors for some of the specialized "line filters." The type of filter that is best for your scope is determined by the telescope's aperture, focal ratio and exit pupil. It is best to consult a vendor like Astronomics for advice before purchasing one. For 6"-10" Dobs, narrow band filters like Orion Ultrablock or (until recently) Lumicon UHC are highly useful in the suburbs as well as dark sites. Narrow band filters allow only a few specific wavelengths of light and enhance contrast on most nebulae (except M-1 which radiates in white light for some reason). For scopes 8" and larger, O-III (pronounced "oh-three") filters allow only the Oxygen-III wavelength to pass. This greatly enhances contrast on emission nebulae (like M-42 or the Veil) and planetary nebulae. Keep in mind that these are all "nebula filters" not "galaxy filters." Objects that radiate in white light are not generally helped by filtration. A 1.25" nebula filter will set you back about $100.

Planets and the Moon benefit from colored filters, which run about $18 each. The Moon is so bright, some sort of filtration is usually necessary to reduce glare. Neutral density filters reduce glare without affecting color. Also, I find that orange or red filters enhance contrast between light and dark features of the Moon. Venus also greatly benefits from glare reduction. I use a violet filter in my 8" Dob which stabilizes the image and allows only about 10 percent of visible light to pass. For Mars near opposition, I find orange or red filters enhance the contrast of surface features. (N.B.: #25 red is very dark and is not for small scopes.) For Jupiter, a medium blue filter (or green under dark skies) increases "surface" detail including the GRS.

Lastly, let me recommend two items that hardly anyone uses: The first is an eye patch from the drug store. The best way to avoid eye strain is to observe with both eyes open. An eye patch allows you to do that while still covering the unused eye. Second, observing while seated is easier than observing while standing or bent over. Many vendors sell special observing seats, but a common folding chair will often do just as well. The stability afforded by a chair will allow you to pay attention to what you are observing instead of maintaining your balance.