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31mm Televue Nagler versus 32mm Edmund Erfle.

Posted by Mark Swanson   08/29/2010 12:00AM

31mm Televue Nagler versus 32mm Edmund Erfle.
Hello, On a night of good seeing at a star party in Ft. Griffin State park near Albany, Tx, I compared these 2 fine eyepieces. I looked at various open clusters and dense star fields for the comparison. My telescope was a well collimated 8" f10 Celestron SCT with starbright coatings and a William Optic 2" star diagonal with 97% reflectivity.

Both of these eyepieces had 42mm field stops, 6 elements, around 18 mm of eye relief, 2" diameter. The Televue weighing 35.2 ounces and the Edmund 10.5 ounces.

It became clear pretty quickly that the 31 Nagler was much better corrected in the outer 35% of the field. The Edmund started to show the Plus + signs of astigmatism. The whole field of the 31 Nagler was pretty sharp. The Edmund had a usable field of up to 80%. The rest would be useful for finding objects on the edge and for framing purposes.

It also was equally clear to me that in the centerfield position the Edmund was unmistakably sharper and had noticeably better contrast than the 31mm Nagler.

I believe that the only area that the 31mm Nagler beats this Edmund 32mm is in the outer 35% of the field. The Edmund was sharper in the central area of the field and the contrast better in the Edmund.

The 31mm Nagler had blackout problems. More difficulty getting the eye in the best viewing position. Eye placement on the Edmund was not as critical. It was an easier view requiring much less work to find an ideal view with no blackout effect.

I have compared this Edmund 32mm Erfle to many eyepieces over the last 20 years. It is sharper on axis than any plossl, 1RPD, Proxima,etc. It comprises 3 achromats and is tack sharp.

There are many different eyepiece designs and I guess it depends to some extent what people are looking for. I have noticed that all Televue eyepieces are sharp on edge, but there is little else positive that I have to say about them. I personally do not like pincushion distortion and would rather have the flat fields.Companies like Nikon and Pentax and Meade do not have to list pupil guidelines. Televue has to because their design has blackout and eye relief problems and all of them seem to have pincushion distortion.

Some of the best eyepieces I have used are made by Harry Siebert. In particular the Ultra series. I also highly recommend the Celestron Ultimas, Antares Elite plossl, Orion Ultrascopics. The sharpest eyepieces I have ever used in scopes that are f7 and over is the Brandon by Vernonscope.

There is a place for all of these designs. It depends on what you want out of your set of eyepieces.