Astronomical Society

of Long Island

 
NEW_ASLI_Home.html

The Telrad Finder & The Rigel Quikfinder

These finders, to my mind, are the best finders you can put on your telescope, no matter what kind of scope, or what size.

They cost forty bucks at your local telescope store.  So why these finders instead of other ones? “Don’t I want a telescope as my finder on my telescope?”  No you don’t and here is why:  If you were looking for the planet Jupiter, for instance, what would be the easiest way to find it in the sky - looking with both eyes, or looking with one eye through a long towel paper tube?  If you have a telescope as your finder, your view of the sky is severely limited.  The Telrad  and the Rigel are “zero power” finders - they do not magnify at all.  And they do not limit your view of the sky at all - one eye can look through the finder and the other eye looks beyond it to see the whole sky.  Jupiter or any other target will be much easier to find.


Here is the other significant feature.  The illuminated reticle that you see projected into the sky with the Telrad consists of three concentric circles.  They are calibrated thusly: the outer ring is 4 degrees in diameter, the one inside that is 2 degrees, and the inner one is 1/2 degree. The Rigel has only the two inner rings. Many of us have the Rigels. They are smaller and have blinking reticles - very useful, very convenient, especially for smaller telescopes that cannot fit the larger Telrad form factor.


This is what the illuminated Telrad reticle looks like.


Having a size reference as part of the finder adds a scale that can be used as a reference in figuring out how far one object is from another.  If you just have a dot, or a single circle, as in some finders, you have no useful “ruler” to determine distances between guide stars and objects you are looking for.

If you use paper sky charts, you can make a reticle in the same scale as your chart, using a piece of acetate as shown below:

This is the Telrad reticle, done in ink on a piece of acetate shown on a page of Sky Atlas 2000.  It is centered over M-97 in Ursa Major.  You can see that the outer ring of the reticle just touches beta Ursa Majoris, which is a helpful reference.  After placing the acetate overlay on the chart and checking the geometric relationships to nearby stars, then you go to the telescope, and place the Telrad bullseye in the same relationship to the stars in the sky, that you had on the star chart.  Your target will now be found in the eyepiece.


Many astronomy applications for computers and handheld devices include the option of displaying the Telrad reticle in the application, so you can position your target under the reticle and see the relationships to nearby stars.

The Rigel Quikfinder

The Telrad