TELESCOPE ACCESSORIES

By Chuck Hawks


The purchaser of an astronomical telescope quickly discovers that there are several additional items, not usually supplied with new (or used) telescopes, that he or she needs to enjoy amateur astronomy. This little article is intended to briefly explore the most common and useful of these.

Tripods and mounts

The mounting system is as important as the telescope itself and often costs as much. Telescope mounting systems can be alt-azimuth (trains up/down and right/left, like a camera tripod) or equatorial (traverses in an arc that matches the movement of objects in the night sky, plus up/down). The lateral arc movement of an equatorial mount is called right ascension (RA) and the up/down movement is called declination (DEC). Equatorial (EQ) mounts require more set-up effort than alt-azimuth (AZ) mounts, but they make compensating for the earth's rotation easy.

The two most common forms of EQ mounts are called "German equatorial" and "swing-through fork." A complete mounting system consists of a mount head (German equatorial, for example) and something to support it, such as a tripod or pier. Either type of mounting system can be designed for manual operation or for locating astronomical objects by means of a computerized/motorized system called "go-to" my most amateur astronomers. Go-to mounting systems are more complicated to learn how to use and usually more expensive.

Many astronomical telescopes come with a freestanding tripod/mount or portable pier for field use, but some (like most Stellarvue refractors, Tele Vue refractors, Questar Standard 3.5 and others) do not. If yours did not, chances are that the manufacturer of your telescope offers a complete mounting system (at additional cost, of course). My advice is to buy it. Table top tripods and ordinary camera tripods are not suitable telescope mounts.

If you built your telescope yourself or somehow acquired one without a mount, Celestron, Apogee, Tele Vue, Stellarvue, Vixen, Meade, Questar and Losmandy sell mounts separately. The Celestron CG-5 is a popular "go-to" German Equatorial mount suitable for use with a wide variety of telescopes, while the Vixen GPD2 is a similar size manual German equatorial mount. Both are good quality mounts and reasonably priced.

Solid and easy to use AZ mounts for telescopes of various sizes are available from Celestron, Stellarvue, Tele Vue and Vixen, among others. A good AZ mount should have some provision for accurately aiming the telescope, usually in the form of "slow motion" controls. AZ mounts are quick to set-up in the field and easy to understand and use. Many experienced amateur astronomers have both AZ and EQ mounting systems, choosing the mount most suitable for the purpose at the time.

Heavy duty, professional video tripods with fluid heads can sometimes serve as satisfactory field mounts for compact spotting scopes or very short focal length refractors, such as the Stellarvue NightHawk, Celestron C-90 and Questar 3.5. These, however, usually cost as much or more than the manufacturer's tripod/mount designed specifically for your telescope and lack slow-motion controls. Bogen and Gitzo are good sources for professional photo tripods and fluid heads.

Finder scopes

Most astronomical telescopes come with some sort of finder scope. If yours did not, you will need to purchase one. Without a good finder scope it is nearly impossible to find objects in the night sky. Even if your telescope came with a finder scope, it may not be easy to use or of sufficient quality. Don't put up with an inferior finder scope; replace it with one you like. A good finder scope is a joy to use and, once it is aligned with the optical axis of your telescope, a great help in aiming your telescope at the target. A bad finder scope is a constant source of irritation.

I prefer a right angle, correct image finder scope. The right angle eyepiece makes the finder much easier to look through when the telescope is aimed skyward. It is natural (at least for me) to move my telescope in the direction I want to go according to the finder image, rather than in the opposite direction (as required if the finder image is reversed or upside down). Whatever kind of finder you prefer, get it.

Most experienced observers recommend at least a 6x finder scope (like a 6x30mm) with a thick, easily seen crosshair that allows the telescope to be aimed at objects invisible or difficult to see with the unaided human eye. A magnifying finder scope is the most accurate way to manually aim a telescope in the field. Many prefer an 8x50, 9x50 or higher magnification finder to aid in "star hopping." I have used optical finder scopes from 4x to 9x and find that, for me, the magnification is less important than bright, sharp optics and an easily visible crosshair. Some finderscopes have an illuminated crosshair and that is a very nice feature. Celestron, Orion and Stellarvue are good sources for magnifying finderscopes.

Serving the same purpose as a finder scope, but without magnification, are red dot sights from Telrad, Celestron, Orion, Stellarvue, Tele Vue and others. These project a red circle or dot on a glass, like a "Holosight" gun sight and are easy to aim at a visible target in the night sky, since you can aim your scope with both eyes open. They can be mounted to the telescope's mount rings, rear cell, or by simply sticking them to the telescope tube with double stick tape and they can be used alone or in conjunction with a conventional (magnifying) finder scope.

A third form of finder is a small, green laser pointer that projects a laser beam into the night sky. Mounted and aligned with the optical axis of the telescope, they are perhaps the fastest and easiest to use aiming system of all, although not quite as accurate as an optical finder. I have all three types of finders on my telescope, a Stellarvue Deluxe red dot, Orion 9x50mm right angle/correct image optical finder scope and a Jasper Laser pointer.

Dew shields/ Lens hoods

Refracting and catadioptric (CAT) telescopes have a propensity to collect dew on their front lenses, which, after all, are usually pointed skyward. Dew is a serious problem at night; I have seen it form on the primary mirror at the bottom of Newtonian reflectors, which have tubes far deeper than any dew shield for refracting and CAT scopes. A lens hood, called a dew shield in astronomy, can reduce, but not eliminate, this problem. Refractors often come with a lens hood, but CAT's seldom do.

If your telescope did not come with some sort of dew shield, you must buy one. Usually they are available from the manufacturer of the telescope, but if not, they are available on the aftermarket. Kendrick, for example, offers flexible dew shields in a variety of sizes to fit telescopes from 3.5 to 14 inches. I used one of these on my Meade ETX-90 and it worked fine. Kendrick also sells a dew remover system, which is a heating system to prevent the formation of dew. It is available in sizes to fit most telescopes, oculars and even the Telrad red dot finder.

Star Charts, planispheres and electronic sky maps

In order to find your way around in the night sky, you need a map. Celestron, Orion and others publish an economical set of maps that show the night sky during each season of the year. Along with each map is a brief description of the most important and interesting objects in each visible constellation. This is very useful information, and no one should be without a set of star charts. They are printed on heavy, water resistant stock, and are intended to be taken into the field.

Star charts usually have a planisphere on the front cover. If not, a planisphere can be purchased separately. A planisphere is a handy rotating representation of the night sky placed behind a large oval window that represents your field of view (assuming a flat horizon). You rotate it to set it for the date and time you are observing; it then shows you the major visible stars, constellations and where they are in the night sky. Planispheres can be purchased for a few dollars at most book stores.

More sophisticated maps of the night sky with thousands of objects are available for notebook computers and tablets. (Also for smart phones, but the screen of these is really too small to be adequate for serious astronomy.) Celestron offers an excellent night sky program called "Sky-X First Light." I find a tablet with about an 8"x11" screen to be ideal for use in the field. If you rely exclusively on electronic map programs, make sure you don't run out of battery power!

Red lens and red LED lights

In order to read your sky maps, make adjustments to your telescope and generally find things in the dark, you need a flashlight. Because you don't want to ruin your night vision when you use it, it needs to have a red lens or use red LED's as a light source. It happens that red light affects your dark adaptation less than other colors. Your astronomical flashlight should not be too bright; this is one instance when a dim flashlight is better than a bright one.

Pelican offers the versatile "Mity Lite Mini System" flashlight. This comes as a kit with a replacement halogen bulb, two AAA alkaline batteries and both clear and red lenses, all packaged in a plastic box. It is completely waterproof and also makes an excellent travel flashlight. (Always take along a small, high quality flashlight when you travel; it will come in handy and can literally be a lifesaver in an emergency.) The price is quite reasonable. The major telescope companies, Celestron and Orion for example, offer red LED lights and batteries will last a very long time in them. Celestron offers a disposable Red Astro Lite flashlight for about half the price of a Pelican Mini system or a red LED flashlight. LED Lenser, made in Germany and distributed by Coast Products in the US, has a couple of models with switchable red or white LED's, as do several other manufacturers of "tactical" grade flashlights.

LED Lenser also offers a Headband Light with a red LED and a rheostat so you can turn down the brightness. Remington Arms, Ray-O-Vac and others also offer headband lights with switchable red and white LED's. These headband lights are very handy for field use, perhaps the most convenient of all red lights to use.

If you don't use a red LED headlamp when out telescoping, a battery powered lamp with a red filter is a useful accessory for your folding table (see below under "Portable folding table"). Stanley Tools offers a "MaxLife 369" LED lamp with a self-contained, folding 7" tripod and a set of three colored filters (inc. red) that works well. The light head tilts through an arc of about 100 degrees. You can choose to use one, three, or all 6 of the lamp's LED's. Three batteries fit in each leg of the tripod and the light will run on three, six, or a full complement of nine batteries! It runs for up to 200 hours on a set of nine AA alkaline cells. The discount retail price is around 20 bucks.

Binoculars

Right behind a Star Chart in usefulness for finding objects in the night sky is a decent binocular. Binoculars are really just two small, low power, telescopes mechanically linked together. Because they provide a wide and correctly oriented view, they are very handy for locating objects at which to aim your telescope.

Binoculars for astronomy should be standard size, hand holdable, sharp and from 6x to 10x magnification. Avoid sub-compact binoculars, they are not bright enough at night. They should have an exit pupil (the light pencil you see when you hold your binoculars at arms length and look through the eyepieces) of from five to seven millimeters. This insures that sufficient light reaches your eyes to let you see dim objects.

To determine the exit pupil, simply divide the diameter of the front (objective) lens by the magnification. For example, 7x35mm binoculars have a magnifying power of 7x and 35mm front objectives. Thus, the exit pupil is 5mm (35 / 7 = 5). 6x30, 7x35, 8x40 and 10x50 binoculars all have 5mm exit pupils. 7x50, 8x56 and 9x63 binoculars have 7mm exit pupils. All of these are standard size binoculars and all of these will serve the amateur astronomer well. Top of the line stabilized binoculars are the best of all, but very expensive.

Good binoculars are available from many manufacturers, at many price points. It is best to avoid cheap department store brands (like Jason, Bushnell and Tasco), although almost any binocular will help in a pinch. Most of the standard size binoculars from the major optical companies are quite good. These include Leupold, Nikon, Minolta, Pentax, Canon and Fujinon. Swarovski, Zeiss and Leica, from Austria and Germany, are among the very best. Some telescope companies, like Vixen and Celestron, also offer good binoculars. For more information about binoculars, I strongly suggest reading my article "Binocular Basics," which can be found on the Photography and Astronomy index page.

Oculars (eyepieces)

Your telescope probably came with one, or possibly two, eyepieces (called "oculars"). Unfortunately, you will probably find that you need at least four of these complex little magnifying lenses. A good starting array would be one short focal length/high power ocular, two medium focal length/medium power oculars and one long focal length/low power ocular. Because the actual focal lengths of the oculars you need depends on the focal length and clear aperture of your telescope, I cannot make specific recommendations here. I have written an article which does, however. Its title is "Ocular Recommendations" and you will find it on the Astronomy section of the Photography and Astronomy index page.

Filters

Filters work by subtracting, or blocking, part of the light spectrum. Most filters are designed to screw into the bottom of your star diagonal or oculars. These are the most affordable kind and perfectly suitable for most applications. Others are designed to drop into or screw onto the back of specific telescopes, or (in the case of solar filters) cover the entire front of the telescope.

The most common filter and the only one virtually everybody needs is the neutral density (ND), or "moon" filter. This is usually the kind of filter that screws into your star diagonal and oculars. Since your telescope gathers over a hundred times more light than the unaided human eye, looking at the brightly lit moon is a blinding experience, akin to staring into a halogen flashlight. The neutral density filter is a gray filter that merely reduces the total amount of light reaching your eye, so that you can look at the moon without discomfort. It is like sunglasses for your ocular. Celestron, Meade, Tiffen, Orion, Tele Vue and others offer moon filters at reasonable prices.

Another common eyepiece filter is the polarizer. It serves much the same purpose as the (cheaper) moon filter, cutting glare, reducing the total amount of light reaching your eye and is available from the same sources.

A useful filter for city dwellers is the light pollution reduction filter (LPR). These can be the type that screw into oculars, or the type that fit the visual back of certain telescopes. There are broad band and narrow spectrum LPR filters. What they do is cut down on the sky glow from certain types (frequencies) of outdoor lighting common in cities. These filters are quite a bit more expensive than the moon filter mentioned above, but worth it if you must view from a light polluted site. They are offered by Celestron, Meade, Orion, Lumicon, Tele Vue and others.

Another useful filter, and one which MUST (for safety) cover the entire front of your telescope, is the solar filter. These visually opaque filters can be made of either glass or mylar (both work well). They allow you to safely look at the sun, the only star you will ever be able to examine closely. You will be able to see sunspot and the granulation of the surface of the sun, which looks rather like an orange to me. Because of their size, solar filters are relatively expensive. Thousand Oaks Optical and Celestron, among others, offer good solar filters at fair prices.

As the stickers plastered all over your new telescope warned, NEVER attempt to look at the sun without a solar filter which covers the entire front of your telescope. The sun is not something to toy with; it is a mainline star undergoing nuclear fusion. Your telescope gathers over a hundred times more light than the unaided human eye and if you look through it when it is pointed at the sun, you will be instantly and permanently blinded. The light and heat of the sun will melt the inside of your finder scope, if it is not covered while your telescope is pointed at the sun. Ultimately, the build up of heat from the sun will melt the inside of your telescope. Eyepiece solar filters are not sold by reputable manufacturers because they are not safe!

There are also colored filters, often sold in sets, much like those available for camera lenses, which screw into your eyepieces. Various colors are supposed to enhance your view of certain planets. I have tried these filter sets, but not found them to be very useful. Some observers, however, like them. Celestron, Meade, Tiffen, Orion and others offer colored filters.

Distributors like Lumicon, Celestron, Orion, Stellarvue and Tele Vue offer specialized filters for exotic purposes that cut or pass very specific frequencies of light. These tend to be expensive filters, but they are necessary for observing certain phenomena, such as faint planetary nebula, that are otherwise invisible to the human eye. Try the Oxygen III (O-III) filter for observing dim planetary nebulas.

Accessory cases

A plastic or aluminum hard shell travel case lined with closed cell polyfoam is an excellent place to carry your oculars, filters, red flashlight and other small accessories. It will also serve to keep them organized while in the field. Doskill, Winchester, Pelican, Zero-Halliburton and others offer such cases at prices ranging from low to substantial. These can be purchased at discount sporting goods stores (check out the multiple pistol cases), camera stores and astronomy dealers.

Hard cases and soft Cordura Nylon cases lined with closed cell foam are normally used for transporting and storing portable telescopes. Either type can work well to protect your telescope. I prefer the padded, Cordura type soft cases, as they generally take less space. Hard cases for specific models of telescope are generally available from the manufacturer.

Some manufacturers, such as Vixen, offer fitted hard cases for their equatorial mount heads. There are also cases, usually the Cordura Nylon type, for tripod legs. Orion Telescope is a good after market source for hard and soft cases for accessories, telescopes and mounts at reasonable prices.

Collimators for Newtonian reflectors

These are devices to aid in the optical alignment of Newtonian reflector telescopes. If you have a Newtonian telescope, you would be well advised to purchase a collimation aid, since these telescopes usually need to be collimated every time they are used. These devices allow the user to align a Newtonian reflector much more accurately than is possible by the "eyeball" method. Celestron sells an inexpensive tool which will help you get close and Tectron sells a (much more expensive) three tool set including a Sight Tube, Cheshire and Autocollimator, plus a booklet explaining collimation. This set will really let you dial in a reflecting telescope and is the way to go if you are serious about your astronomy.

Portable chair or stool

Standing up half the night gets tiring and bending over to look through a telescope eyepiece for an extended time is hard on the back. A portable, folding chair or stool will be much appreciated when you are out telescoping. Folding, three-leg camp stools are very economical and can be purchased in most sporting goods stores. They are not optimum, but they are better than nothing. A three leg stool works better than a four-leg stool on uneven ground. Another possibility is a two-step, folding kitchen ladder. These provide two seating heights, but are not as comfortable as a real stool.

Star Bound sells a well-made, steel frame, four-leg Viewing Chair designed expressly for use with a telescope. Its padded seat is easily adjustable in height from 9 to 32 inches and the four-tube steel frame serves as a backrest. This is the best and most versatile observing chair that I have encountered, but unfortunately it is not cheap. It took me a good many years to decide to order mine, but I'm glad I did.

Even more expensive than the Starbound is the three-leg Tele Vue Air Chair, which resembles a short, padded, bar stool. This chair's seat rotates through 360 degrees (a good feature) and height adjustment is easy, but limited in range to between 21-28".

Orion sells a folding, three leg camp stool and two models (standard and deluxe) of their three-leg, adjustable height, padded stools that loosely resemble the Tele Vue Air Chair. These do not appear as well made as the Tele Vue Air Chair and they don't adjust as easily, but they sell for about 1/4 and 1/3 the price, respectively.

Portable folding table

Surprisingly convenient in the field is some sort of folding camp table to hold your star chart, note pad, ocular case, etc. One type is canvas and usually has a couple of built-in cup holders. One of these cost me $5.95 on sale at the sporting goods department of my local Bi-Mart department store. Orion offers a better "Roll-Up" folding table with a wooden slat top specifically for astronomers. Bi-Mart and other department stores carry similar roll-up tables among their camping supplies. It is convenient to have a folding camp stool of appropriate height (not your viewing chair) specifically for use at the folding table.




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Copyright 1999, 2011 by Chuck Hawks. All rights reserved.


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