The Telrad is a one power (1X) sight that was originally designed for installation onto astronomical telescopes as an aid to locating deep sky wonders at night. While it was not developed as a tool for daytime use some of our customers have adapted the Telrad sight for uses we never anticipated, for example many stage lighting technicians adopted the Telrad to help them point spot lights in the theatre.
The Telrad can be employed as the sole or primary sight of a telescope to help you "star hop" using visible stars to find and center objects that would be invisible to the naked eye or in other small finder telescopes. Or, you may choose to use a Telrad in combination with a second conventional magnifying finder telescope. The Telrad is the innovative, dominant choice of finder sights by the amateur astronomy community, and it is not uncommon to find a Telrad on professional observatory telescopes too! It is a particular favorite among experienced amateurs using deep sky telescopes (particularly our larger "Dobson" style telescopes) where aperture and the ability to find faint deep sky objects are concerns; these include our Astro-Systems and other fine Dobsonians by Obsession and Star Master. The Telrad is often the choice to replace economical finders sights provided on telescopes such as the Orion model XT-10, XT-8, and XT-6. Most of the big telescopes found at any star party get-together will probably have a Telrad on it.
However, because of the Telrad's ungainly appearance and moderate bulk the Telrad is not generally selected for use on smaller, fork mounted telescopes.
The Telrad sight is composed of two components: 1) Sight, and 2) Base. The Sight houses the power supply (two "AA" batteries), an on off rotary switch which also can vary the brightness of the display, a red L.E.D. lamp, the Telrad reticle, a mirror to divert the light up towards the 45 degree inclined display window, and a lens to bring the image of the reticle to focus on the window.
Above: Telrad sight reticle pattern projection arrangement (not to scale):
1. Red L.E.D., 2. Telrad reticle, 3. Adjustable tilt flat mirror, 4. focusing lens, 5. display window inclined at 45 degrees shown with simulated projected reticle. (6,999 bytes).
The Telrad optical arrangement is simple, and yet reliable. It provides that the Telrad's distinct pattern, adjustable in brightness, will be projected by a long life red Light Emitting Diode onto the display window. When the window is viewed from the observers vantage point then the pattern will appear to float, apparently suspended in front of the stars or other objects in the background. The Telrad sight is delivered from Company Seven with the reticle pattern focused onto the window. The focus is factory set by the adjusting the spacing between the L.E.D./reticle assembly and the focusing lens. The L.E.D. and reticle assembly are cemented into place within the Telrad housing. One must use care when installing or removing the two "AA" batteries (optional - not included with the Telrad) not to dislodge the L.E.D. reticle assembly.
Telrad Sight Reticle Pattern — display set to near maximum brightness to show up better in photograph.
The reticle pattern is scaled so that each one of the three circles appears to cover a set area of sky: 4 degrees for the outer circle, 2 degrees for the middle circle, and 1/2 degree for the circle in the center. And so Star hopping (moving from one star to another) with the sight is very easy:
* the view through the window is "normal" and not reversed left to right, and up side down as is common in many telescope finderscopes,
* one may clearly see the area of sky around the Telrad window,
* the three projected circles help one to learn how to judge angular distances from one object to another.
* the intensity of the reticle can be varied, and with the optional Telrad Pulser blinking circuit kit it can be pulsed on and off repeatedly.
Each Telrad sight is sold furnished with one sight Base. The Base must be installed onto a telescope at a position that will assure:
* the Telrad will not interfere with movement of a telescope - such as in a fork mount.
* the display window will be positioned at a point behind which the observer can easily view the window.
* the sight display axis will be close in line with the optical axis of the telescope, this is to facilitate the alignment of the displayed reticle pattern with the target seen in the telescope.
The Base is best left attached on to a telescope by any one of several ways, this is usually either by double sided adhesive foam provided with the base or by attaching the base with mounting screws through the provided holes in the base. The Base could be strapped onto a telescope, or attached to an accessory plate by those who do not wish to risk marring the expensive finish of a fine telescope. Once the Base is attached to a telescope then the Telrad can be positioned onto and then secured to the Base by the two furnished metal thumb screws. Extra bases are available so that one may move the Telrad sight from one telescope to another.
The center of the window is about 3-½ inches (89 mm) above the platform (telescope, stage light, etc.) upon which the Telrad is installed, and so seeing into the distance through the sight depends on being able to have the Telrad window remain above obstructions that might be in the way. The optional Telrad Riser is an accessory for the Telrad sight which elevates the Telrad from the Base by either 2 or by 4 inches. The Riser can be installed quickly and with no tools by the user. The Riser is available in either 2 inch or 4 inch heights, these are installed onto the Telrad Quick Release Base and the Telrad sight is installed onto the Riser. The upper platform of the Riser resembles the Telrad Base and accepts the Telrad Sight, while the bottom of the Riser matches the arrangement on the bottom of the Telrad Sight and thus fits perfectly into a Base. These Risers can even be stacked if desired to attain greater elevation.
Once the Telrad sight is installed onto the Base then then the reticle pattern must be aligned so that both the telescope and sight are centered onto a distant target. This adjustment my be made during the day or evening. The adjustment is easily managed by the three focus dials located at the rear of the sight housing. These three dials permit the user to tip or tilt the internal flat mirror to shift the position of the pattern on the display window.
Use of the Telrad
To locate an object with the aid of the Telrad, simply move the telescope so that a bright star or other object near the desired object comes into the display window of the Telrad. if the desired object is bright enough to see in the Telrad sight, then simply center the object in the center circle of the Telrad, and then move to the main telescope for detailed look. If the object to be viewed is fainter than what can be seen with the naked eye, then use the Telrad to navigate onto the target by "star hopping".
Some examples of "Star Hopping":
1) To find the "Rosette Nebula" in the constellation "Monoceros": Move the telescope to center the Telrad onto the bright star Betelgeuse (in Orion). Move the telescope to the left (west) about 2-1/2 Reticle diameters. This should put the telescope just about centered onto the Rosette Nebula.
2) To find the "Ring Nebula" in the constellation "Lyra": Center the Telrad onto the bright star "Vega". Next move the telescope about two Reticle diameters (about 8 degrees) south east over to the two brightest stars nearest to Vega; these will be the stars "Sulafat" and "Sheliak". Move the telescope to position the stars "Sulafat" and "Sheliak" on the middle ring of the reticle at 9 and at 3 o'clock positions. The "Ring Nebula" should be just about centered in the Reticle.
The more you practice this skill, the easier it becomes to use the Telrad. And a side benefit will be that you improve your own ability to judge angular separations.
You may find it helpful to plan your first several observing sessions by using a star chart, with a properly scaled transparent "template" which shows the Telrad Reticle pattern. The template may be placed over the chart to help one navigate across the sky. You may purchase any of a number of commercial star charts which include a Telrad sight pattern overlay.
One mounting base is included.
|Window dimension (from observers vantage):
||1-5/8 x 1-3/8 inch (41.3 x 35 mm)
||1x (zero power)
||Black finish, ABS plastic construction
|Retaining thumbscrews (two on the Base):
||6-32, ½ inch long
|Length overall length:
||8-3/8 inch (21.3 cm)
|Height overall (on Base):
||5 inch (12.7 cm)
|Weight with Base and batteries:
||10.9 oz. / 308 g
||Two "AA" 1.5 Volt, in series
|Packing box dimensions:
||10-1/4 x 6-1/2 x 4 inches (26 x 16.5 x 10 cm)
||14.9 oz. (0.42 kg)