elkcub said:
Sorry to take this long in responding. I didn't notice your post.
Swift refers to the 5-element eyepiece as an Erfle ocular. I don't know the difference from a Konig design, but apparently the Erfle type is used for wide field applications. There are 6-element versions too.
I get the feeling that you may have been using one of the early large body type Audubons with 445 ft. FOV and 11-12 mm eye relief. The later small body Type 4's and the current Model 820 with 430 ft. FOV have a much nicer eye relief of about 14 mm. Could you take a look at our article on Post #15 and tell me which model you had?
The Type 4's, starting with the 804R, and Model 820 also have first class multi-coatings. They are commonly found on eBay at reasonable used prices, and will be re-collimated, if necessary, by Swift for about $60. This is one instance where I think a repair cost is very reasonable to get this kind of value.
Ed
Hi Ed,
I scanned through your fine history, and I can tell you with some certainty that I had the 804 4b2. It was definitely fully-multicoated. Maybe it technically had 14mm of eyerelief, but it still cut off a good 20% of the FOV for me. As Steve Ingrahm pointed out, this still leaves an eyeglasses wearer with a large FOV. I just really like to see the field stop when I look through binocs.
Interesting about the Erfle 5-lens design. I think that Edmund Optics still offers an Erfle-design telescope eyepiece. From what I have read, Erfles have a wide FOV but definitely lose resolution on the outer part of the field. Konigs, I think, are much more prevalent these days in lower-priced wide-field eyepieces. It too apart an inexpensive binoc once -- a Swift Plover, I think -- and saw that the eyepiece was a Konig design. Shockingly, one of the lens elements was plastic! (I really try not to take binoculars apart because I have never put one back together again).
The super-duper wide-field telescope eyepieces, the Naglers, Pan-Optics, etc., have over 8 elements, I think, and may be a variation on the Erfle design. These kind of eyepieces are huge, and would really weigh a binocular down -- not to mention, all those elements really dim the image. However, with new thinner lens designs, and an oversize objective, I am thinking you could build a dream binocular -- say an 8x56 with 8-element Nagler type eyepieces, and 80-degree FOV sharp to the edges, with the brightness of a good 8x42. Porro-design probably, to get the big prisms necessary. And with a reinforced polycarbonate body and modern thin-lens design, it wouldn't weigh much more than the Audubon 804.
At any rate, I'm no engineer. Just a dreamer.
By the way, it was indeed the Swift 825 7x35 roof-prism Audubon that I owned for a short while.