Last updated: 17 December 2005
Subject: Surplus Shed 2-Inch 38mm Erfle Sent: Friday, December 16, 2005 22:00:13 From: The Brown Family (email@example.com) Still enjoying your sight, along with my ETX90!! Here is my latest eyepiece review, with a twist! Chris Brown Surplus Shed 2-Inch 38mm Erfle. I am constantly searching for a lower power/wider field of view with my ETX-90ra. I usually employ my trusty 32mm Sirius Plossl for 39x and a little over 1.3 degrees true field. I have also tried a 42 Ultima, for 29.7x, but the eyepiece gave me a severe case of "tunnel vision", kinda like looking through a long tube to see the image! As an experiment, I held up my 2-inch Surplus Shed Erfle to the ETX-90, and in moments of steadiness, the results looked promising! Retailing for $47.50, the SS-38 is a 5 element 60 degree Erfle made of some kind of plastic mated to an un-threaded 2-inch aluminum barrel. I had an old chromed 1.25" barrel handy, so I measured, shimmed, measured again, and finally attached it to the Erfle with epoxy putty! The new barrel hangs down below the original by about .75", and does not block the light-path, therefore making it still useful in a 2-inch focuser. The result is about 33x, a wide 1.8 degree true field, and a useful 16mm eye relief, so you don't have to be in the next block to see the image! I was also surprised at the lack of "Black-out" effects! I was most concerned about clarity, and edge-of-field performance with this strange set-up, and I was not disappointed. I pointed to M42, and was able to split the 4-star trapezium easily! The nebula was obvious, even in my hazy, backyard conditions, and I was able to fit the three "sword" components into the FOV, but just barely! Edge of field was tested on M45, and while all seven sisters barely fit in the rather soft field stops, the very outer stars were still very tight, with only a slight amount of "mush" in the otherwise pinpoint field. Furthermore, moving your eye around seemed to clear up the outer stars, but by keeping a steady eye, I was rewarded with the widest FOV I have ever seen in an ETX-90, complete with a vivid "spacewalk" feeling! Achieving focus was not a problem, nor was the weight of the eyepiece, due to its lightweight construction, but it looked kinda awkward, like balancing a small pineapple on the end of my little Mak! I consider the 38mm 2-inch Erfle eyepiece to be totally usable in the ETX-90, and the experiment to be a great success! My search for the ultimate low-power eyepiece continues; I have a 1.25" Celestron Kellner (only three elements!) 40mm "Japan" eyepiece on the way, and I also noticed that The Surplus Shed sells a 41mm Erfle in 1.25" format. Hmmm... Updates pending... Chris Brown
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