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Celestron Erfles

Started by Inge_S, 12/09/2002 09:22AM
Posted 12/09/2002 09:22AM Opening Post
Dedicated amateur astronomer Antony Allsobrook (NZ) kindly sent me a set of four Celestron Erfle eyepieces for testing and comparison with UO-eyepieces. I was a bit sceptic in advance, since the comments I've heard about Erfles mostly have been reluctant or negative. This weekend I had the opportunity to try the eyepieces, not from a very dark site, but from my driveway (suburban conditions). I use an 8-inch f/6 Portaball Newtonian with Zambuto optics, and have only UO orthos and one Konig in my personal set of eyepieces.

The Celestron Erfles are 1.25" barrel eyepieces, and available focal lengths are 16mm, 20mm, 24mm and 28mm. I don't know the nominal field of view, but it must be something near 70 degrees. The design is classic and functional.

I was quite surprised when comparing the 16mm Erfle with my 16mm Konig. The field of view is more or less the same for these two eyepieces, and both suffer from some edge coma. However, this was much less conspicuous for the Erfle than for the Konig. I also noticed that the image brightness was excellent in the Erfle. Possibly the sharphess near the centre of the field of the Konig was slightly better.

I tried all four eyepieces, and the general impression was the same. Images were crisp and sharp, and with normal use edge coma was not noticeable. I also found the eye relief to be comfortable. Perhaps the 28mm had a slightly longer eye-relief than what I'm used to, but it was much better than e.g. the 25mm UO ortho where I find field blackout to be annoying.

I used the 28mm with an O-III filter on extended nebulae like the Veil, the North America nebula and NGC281 in Cassiopeia, and I'm very pleased with what I saw. I have never before had such a good view of the North America nebula. With the wide field of view, much of the nebulosity could be viewed simultaneously, and the "Mexico" region was very conspicuous. The two main branches of the Veil were visible without a filter, and absolutely great with the O-III. I could even easily see the Crescent nebula in Cygnus (NGC 6888). I consider this to be pretty good with an 8-inch with such an amount of ambient light.

My general impression of the Celestron Erfles is that they are great eyepieces, and I will try to obtain at least one of them for myself. I can't give any statements about how they compare with e.g. Meade wide angle or UWA's, but I can definitely recommend them for persons who can't use 2" eyepieces.

Antony Allsobrook kindly allows me to keep the eyepieces for some time, and I will also test them with our new club scope, a 12.5" f/4.5 NGT Newtonian. I will report the results as soon as they are available.
Posted 12/09/2002 02:32PM #1
In addition to the 4 eyepieces you listed, Celestron also had a 32 mm Erfle. If memory serves me correctly, the 20 mm was the first available followed by the 16 mm and the 32 mm in the early 80's and then the 24 and 28 mm eyepieces. These eyepieces are "fully coated" not "fully multi-coated". They were eventually replaced by the silver top Plossls. (Mid 80's or a little after.)

Celestron was generally fairly conservative in respect to balancing the eyepieces with field stops to preserve reasonable edge definition. Accordingly if you compare the Celestron 16 mm and the 20 mm to Meade's "Research Grade Erfles" in 15.5 mm and 20 mm the Meade's will have a larger field size, but the Celestron's will have better edge definition.

I always felt the 24 mm and the 28 mm were particularly nice as the eye lenses were well recessed. This helps with eye placement and minimizes the chance of getting gunk on the optics.

If you like these erfles it may be rewarding if you can find the short lived Celestron Ultima Wide Angles (not the regular Ultima series). These included a 15 mm, 19 mm and 23 mm. I have the 19 mm and it's field lense is a large 23 mm in clear aperture. In comparison to a TeleVue 19 mm Panoptic, the w.a. Ultima has a larger field of view. By field stop/radian/focal length/magnification calculations the apparent field of the 19 mm is a little over 70 degrees. Additionally this series is fully multi-coated.

Barry Simon