There are a lot of accessories that you can buy or make to augment your astronomical adventures. Before you go buy a bunch of things you may not use, gain some experience first and then you will have a better idea of what you will need. Some of these accessories can run into the hundreds of dollars or more, so try to borrow them from someone for a bit to see if it would help. This is a list of just some of the accessories available. We aren’t advocating any as necessary nor are we promoting any brand names (where mentioned). We are focusing on accessories for visual astronomy and not on astrophotography. Many first time telescope buyers will buy a kit that includes everything you need to get started including some accessories.
Filters can significantly enhance what you see through an eye piece by blocking out unwanted light increasing contrast with the light waves, or colors, you are interested in. Filters help a great deal with deep space objects (DSOs) that emit light and as emission and planetary nebulas and are less useful for other DSOs like galaxies and star clusters. The reason is because emission and planetary nebula emit light in specific ranges of light while other DSO emit across a broader spectrum. The benefit of a narrow band filter will depend on a number of factors like how dark a site you are in, the seeing, and so forth. Agena Astro Products has an extensive article on filter types and uses that is worth reading. Broadband filters like so-called light pollution filters can help somewhat in suburban skies because they filter out wavelengths generated by common street lamps like low sodium bulbs, both with the proliferation of LED lights, the benefits of light pollution filters are somewhat reduced.
Polarizing filters that are either at a set light reduction or a variable polarizing filter can help bring out details on bright objects like the moon and planets. Anytime the moon is more than 1/4 it can be blinding to look at in a telescope and a polarizing filter knocks down the light levels and also removes light waves that are no parallel which enhances contrast and detail. The benefit of a variable polarizer is that you can get the benefits of polarization while reducing the loss of light which is useful with planets.
Solar filters can be used to use your telescope to look at the sun. Be sure to follow the instructions and if they are damaged in anyway, do use them. Looking at the sun through a scope with a damaged filter can lead to immediate retinal damage or blindness.
Viewing aids help us see objects in the sky and are often only needed for specific uses or requirements.
A Barlow lens is used to multiply the magnification of an existing eye piece. Using a special set of lens, a Barlow can double or triple the magnification of an eye piece. For example, a 2x Barlow can turn a 22mm EP into an 11mm. There will be some loss of image quality but its usually not noticeable. It’s a lower cost alternative to having EP’s at focal lengths you don’t often use such as short one for high magnification.
Focal reducers are the opposite of Barlows. Focal reducers use a series of lenses to artificially shorten the focal length of a telescope allowing for faster focal ratios which brightens objects and produces a wider field of view. Focal reducers are often used for astrophotography but with the growth of electronically assisted astronomy (EAA), focal reducers speed up image capture. For example, a 6.3 focal reducer can turn a F10 SCT into a F6.3. Focal reducers tend to be specific to a model of telescope.
Camera adapters are used to attach a DSLR to a telescope for astrophotography or EAA. Adapters usually have a tube that fits into the focuser and then an adapter that fits a specific type of camera such as a Canon or Nikon. You can also buy adapter kits that can be used with smartphones with some success.
Dew shields are heated or unheated tubes that are attach on the objective end of a telescope and help reduce the formation of dew by shielding the objective from cooling air currents. Dew shields can also increase contrast through the eye piece by blocking ambient light from entering the optical system. Because the rays entering the telescope from celestial objects are parallel, a dew shield won’t impact field of view.
Dew heaters are bands that are wrapped around an optical instrument like the objective, EP, or finder scope, or attached to the mirror assembly of Newtonian mirrors. Dew heaters should warm the instrument to just above ambient temperature so they don’t dew or frost over. Some dew heater systems come up controllers that manage the heat output based on ambient temperature while lower cost, USB powered ones have no temperature control or only low, medium, and high.
Collimation tools help you to collimate, or align, telescopes that have adjustable mirrors like reflectors and catadioptrics. Collimation tools include lasers that insert into the eye piece and you have to center the beam or visual tools like Cheshire eye pieces.
Setting circles are used primarily astronomers that have manual telescopes and want a way to easily point their scope at a target. Like computerized and motorized mounts, setting circles have to be polar aligned for each session. You do need a way to convert declination and right ascension coordinates to altitude and azimuth.
Digital setting circles (DSC) use encoders attached to the altitude and azimuth axes of the mount, and a small computer to keep track of where the telescope is pointing by counting steps from the encoder. The higher the number of steps, often measured in the tens of thousands of steps, means better accuracy and resolution. Then, the controller or a tablet or laptop attached to the DSC shows you the difference between where your scope is pointing and the object you want to see. By moving the telescope, you can land on the target. Some controllers have a small data base of objects but you’re going to want to use a tablet or laptop with planetarium software installed because it will be easier and more versatile to use.
Standing out over a telescope for hours is a lot of fun but it can also be uncomfortable especially if your cold, leaning over to peer through an eye piece, or can’t readily find your tools and other items you bring with you. Some basics will make your time under the stars much more enjoyable.
An observing chair is an adjustable, light weight chair/stool that lets you sit comfortably at your eye piece for long periods but can also be adjusted and moved quickly and reliably. There are many types to buy or make, if you like DIY, but make sure it is light weight, adjustable, stable, and painted a light color so you can find it at night.
A diagonal is a piece of optical equipment that bends the light path 45 to 90 degrees so you an position the EP at a more comfortable viewing position. Some diagonals will also correct the oritntation of the view at the EP so that you don’t have to mentally flip the image left/right or up/down when comparing to a star map.
Cases hold all of you bits and bobs that you’re carrying out into the field. There are numerous types of cases available–too many types to list–but you want a case that you can customize for your needs, will securely hold your eye pieces and other optical components like filers, and helps keep your organized. Cases that open like luggage are good because they provide easy access to everything.
Red light or a red flashlight so you can illuminate your area without impacting your night vision too much. Be wary of the LED red flashlights that are sold by big retailers. They can be extremely bright which will blow out your night vision. Celestron makes a variable brightness red light that works well, but cover the lens with a piece of matte tape so even out the light a bit.
Laser pointers are useful when you are with others and you want to show them a constellation or other object. They project a red or green light into the sky which can be seen from those near by. Just be careful not to point it at people or airplanes. Also, be mindful if there are astrophotographers in the area as laser lights can ruin long exposures.
Warm clothes, of course, but just remember you are spending much of your time standing still so add on extra layers especially for your feet and hands. One of our members, Jeff Higgins, recommends buying cheap, thick soled boots 2-3 sizes too large, and then layering wool and cotton socks to insulate your feed, wick away moisture, and keep your feet toasty. Might be worth getting battery powered hand and foot warmers.
Mike Fratto is an amateur astronomer who can be found in his backyard or at Darling Hill Observatory on the rare nights its clear in Central New York.