Hitting the bull’s eye with a Telrad
Have you purchased your favourite astronomical magazine for this month yet? I am sure you are familiar with the vast amount of pages devoted to telescope accessories and have made a mental list of all the gear you would like to purchase in the future to compliment your astronomical observing which brings me to the ‘point’ of this article. Having a good telescope is one thing however being able to point it swiftly and accurately to a star or galaxy in the night sky is another matter entirely.
All telescopes must have a finderscope attached to its body. These finderscopes are like miniature refracting telescopes often with a magnification of 8x and an aperture of 50mm with a cross hair at one end. This set up is very much like a scope on a hunter’s rifle. Assuming the finder is lined up with the main telescope it should be a simple matter for the observer to peep through the finder, align the centre of the cross hairs on their target and return to the eyepiece with their desired target at the centre of the telescope’s low power field of View (FOV). Simple and elegant but unfortunately life is not so easy especially for the beginning observer. The process of extracting a galaxy from the sky using a finderscope is a bit of an art form which requires many hours of practice and moreover these finderscopes tend to have an upside down FOV confusing the observer again. If you are cross checking a star atlas illuminated by your faint red torch with the inverted finder’s view, one is often left feeling defeated and agitated. The solution? Get yourself a Telrad!
The Telrad is a 1x type reflex sight which offers no magnification at all. This black plastic box attaches anywhere on your telescope via the supplied base plate using adhesive strips or screws and is powered by two AA batteries which could last you a year without replacement. The Telrad projects a red illuminated bull’s eye pattern onto a glass plate which can be seen against the starry background with the naked eye. The illumination can be adjusted by a switch located on the right hand side for various kinds of observing. The very dim and almost invisible setting is favourable for preserving dark adaptation under very dark skies when hunting down faint galaxies and nebula while the brighter setting can be used under a strong moonlit or light polluted sky.
Aligning the Telrad is easy. Once mounted with e.g. Polaris in the FOV the bull’s eye pattern can be shifted in any direction using three knobs mounted at the rear of the box below the glass aperture. The bull’s eye itself is made of three separate circles with angular sizes of ½, 2 and 4 degrees which will assist users in measuring the angular diameter and separation of naked eye subjects such as star clusters to size estimates of the comas and tails of bright comets. With a little practice the user will become very proficient often finding faint targets invisible to the naked eye like M81 within seconds.
The Telrad is a very versatile accessory which has stood the test of time even beating today’s modern new kids on the block. The Telrad is more than just a fancy finder as it offers the chance for beginners to pursue more advanced forms of observing as it will show exactly where your telescope is pointing to within an accuracy of 30 min’s of arc. Anyone who undertakes the serious study of the deep sky, variable stars and comets etc. will find the Telrad a gift sent from heaven.
With a Telrad you form an instant communion with the sky. Light, versatile, accurate and fun, let the Telrad point the way. I never observe without one so acquire one for yourself and experience a new and refreshing way to observe the night sky!
Martin McKenna
