Sometimes the simplest devices are the most ingenious. The week, we take a look at the astronomer’s secret weapon; the Telrad Finder. Anyone who has spent any amount of time with a telescope knows that accurate pointing is a true challenge. When you are sweeping the sky at even moderate magnifications, you may be looking at a field of view much smaller than the Full Moon, itself only the size of a fingernail at arm’s length. This gives you a “tunnel vision effect,” and finding even bright objects can be difficult. Add to this the disorienting fact that you have to look down into an eyepiece, the image may be inverted both left to right and/or upside down, you’ve got a line of impatient viewers, and well, you get the idea. What you really need is a finder that simply “paints” your aiming point in the sky-your own personnal astro bat-signal…that’s why you learned those constellations, right?
Enter the Telrad, a simple but elegant device that graces the tubes of many a telescope, both professional and private. In the late 1970’s Steve Kufeld adapted the low-tech device from early World War II bombsights and applied it to astronomy. In fact, we see a distinct similarity between the Telrad and the F-15C Eagle illuminated gun sight reticule. The Telrad simply acts as a “heads-up display” for your telescope. I first used one while working at the Flandrau observatory in Tucson, Arizona. We had one mounted on either side of the telescope for quick observer access, and they served as a good “sanity check” for the pointing software as well as a good manual backup for slinging the 16” around. I resolved to get one of my own, and now a Telrad base mount is standard on every telescope I own or build. I can attest that the Telrads work better than any stock finder, and even with many imitators on the market, the original design is pretty much unchanged.
Telrad as mounted on the trusty Astroguyz C8″…
Telrads are simple “1x” magnification finders; they place 1,2, & 5 degree field of view circles on a glass over an unmagnified sky. The reticule is a night vision-friendly red cast, and can be easily dimmed by a rotating switch. The base is attached along the axis of the scope via adhesive, and two quick release screws allow for easy removal of the device. This is true genius, as you can own one Telrad and buy separate mounting bases for each scope you own.
Telrads are quickly boresighted by tweaking the mirror alignment with three small knobs located at the back of the device. Simply aim the primary telescope at a bright target such as the Moon or Venus and then align the center of the Telrad on the same object. You’re now ready to go after faint fuzzies! In fact, more than a few celestial guide books and planetarium software programs now overlay Telrad circles on sky charts for reference. This device harkens back to the tried and true method of “star hopping” to a target, a good skill to have when the laptop battery dies, or your computer pointed scope insists on aiming at the ground. Don’t forget to check the alignment of your Telrad periodically, especially if you’ve just remounted it.
The device runs on 2xAA batteries, and accepts rechargeables just fine. Fresh batteries will last throughout the night, and I’ve often left the device turned on, only to find it still running fine days later! They also add very little by way of weight or bulk to a telescope and are very durable; I can attest to this personally as ours sat in a flood for several days! A simple clean up, and the device continues to perform admirably. Another fun fact that is often overlooked is that you can look down into the device for field orientation, handy when your telescope is oriented at neck-bending angles. This trick makes them perfect for a low to the ground Dobsonian telescope…
In closing, Telrads fall into that rare category of devices that are simple and just work. Once we started using one, we can’t imagine how we got along without it. Telrads new run for about $40, and extra base mounts run for around $10. Another good investment is a dew shield, as the glass is prone to fogging up during those humid evenings that pervade places like the US Eastern Seaboard. These run about $13 new…If you are looking to upgrade, or simply want to make a good telescope great, a Telrad is definitely the way to go!
Telrad: The view from above!