ASE logo Astronomical Society of Edinburgh


No. 48 - June 2005


The Televue Radian eyepiece

At the May meeting of the Society Gary Poyner recommended that anyone wishing to look at faint objects whether they are galaxies or stars should consider purchasing a Radian eyepiece. With this eyepiece, he said, it is possible to see objects of magnitude 14 (with a 200 mm / 8 inch telescope) even in an urban environment.

I wondered if this would be the case. I obtained an 8 mm Radian which gives a magnification of 125 with my 200 mm reflector. Using my old eyepieces, under the best conditions I could see stars of 12.6 mag. Under ordinary conditions 12.2 often seemed to be the limit.

I received the eyepiece in the middle of May. Thus I was not able to test it when the local sky was at its darkest. I, as Gary also recommended, cleaned the primary and secondary mirrors of my reflector. This had not been done for eighteen months but they were not in too bad a condition. I also re-collimated the telescope. When a clear night came along I looked at a group of stars which included one of 10 mag down to one of 14. I was just able to pick out a star of 13.4. I think that after the middle of August I may well be able to see down to 14 (particularly on a moon-less night) though I may have to wear a hood. It is possible that I may have to take steps to ensure that stray light does not get into the telescope by erecting boards to block room lights and street lights. It would also be a good idea to attach a black tube to the end of the reflector.

The Radian has other advantages. I can use it with spectacles. Previously I could only use my 10 mm and 5 mm eyepieces without spectacles. This caused some problems because I have astigmatism. Also the Radian improves all viewing of stars under magnitude 10 because of the quality of the optics and the wide field of view. It is very comfortable to use because even with the drive off it takes a little time for objects to move across the field of view.

For the full specifications see the Televue web site on and look at their section on eyepieces. The cost? Ordering an eyepiece from the UK, at the present time, cost just under £ 200 including VAT and carriage. It is possible to order one from the USA. It seems that you can save about £ 30 minus the carriage cost at current exchange rates.

Des Loughney


Cover page

From the President

Cooling the Earth

See the Sun in a different light

The 2005 Scottish Astronomy Weekend

Z Ursae Maioris

The Televue Radian eyepiece

The Society at work and the City Observatory

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