UPDATE
This thread has been inactive for some time, but several people have read our article and made purchase decisions based on its contents. This post will attempt to clarify a few ambiguous matters:
1. The issue concerning cemented doublets in some 804EDs has been explained by an equally qualified Swift technician in the US. According to him, some repair technicians lost or damaged the thin .6mm air-spacing shim and simply cemented the two lens elements. This, of course, would degrade the image,
since the optical design was based on air-spacing.
2. The same expert has assured us that the current 820ED does
NOT use
air-spaced objectives ..., although so far no one has verified that the view is noticeably different than the standard model. Testimonials are encouraged.
3. A previous side-by-side comparison of my Type 4a 804R (ca. 1987) and a Type 4b(1) HR/5 found no difference in coatings or view. They were both marked "Fully-Coated Optics." A more recent comparison of the same two types revealed that there is a coating difference, evidenced by a uniform light green reflection of the newer model (ca. 1995) vs. the 804R, which is pale purple or green depending on orientation. I am now convinced that the 804R, and perhaps the original Type 4b(1) HR/5, only had partial multi-coatings.
Unfortunately, I have not been able to compare the coatings of the more recent Type 4b(1) with my 804ED (ca. 1997) or a Type 4b(2), both of which are marked "Fully Multi-Coated." So, rather than speculate on the number of coating variations used for Type 4a,b,c Audubons, I would simply suggest that the buyer look for light green coatings.
There is some evidence that an early Type 4b(1) was sold in Europe by Swift-Pyser, which had the same MC optics as the 804R. It is also possible that cover plates on some 804Rs were changed during repair, which would make it appear that way. Unfortunately, hybridization can never be discounded.
The 10x50 Kestrel (ca. 1998) I own is fairly dark green, but not as dark as the current issue Model 820s. Renze just acquired a somewhat older 10x50 that is actually marked "Audubon," and he may wish to comment on the color of his pair.
4. Some time back someone mentioned that Swift 804s were getting rare on eBay. I poo-poo'd that, but at this point I'd have to agree. Nothing much has showed up in the US for months. I've haven't seen an ED version since I bought mine.
As of this date we did purchase a 1994 804ED for Renze on eBay which was overhauled by Nicolas Crista, the chief opticalman for Swift when they were located in Boston. He did a beautiful job, — including installing new cover plates. See what I mean?
5. I purchased a pair of Fully Coated Swift Model 766 7x35 Holiday Mark II (ca. 1978) on eBay to evaluate its 80.15 deg., super-wide 600 ft. FOV. Unfortunately, they were quite dirty inside and in need of collimation, which made the economics a bit iffy. The super-wide FOV is interesting, although frankly I don't know what to make of it. The 1968 catalog said: "The Holiday delivers an incredibly wide field, equal to that of the human eye, without distortion..." This will take some time to understand. In 1971 they sold the same model with a 630 ft. field of view.
Although the 1974 catalog refers to the "... fabulous Mark II features" of Model 766, it turns out that it
does not have BaK-4 prisms. Four-sided edge dimming of the exit pupil clearly shows the use of lower cost crown glass. So, unless someone replaced the prisms over the years with different glass, the Mark II quality illusion is shattered. Is nothing sacred? Curiously, this model sold for exactly the same price as the Type 1 and 2 Audubons in their day, but unlike the latter it displays
serious prism reflections that are very distracting.
6. Ending on a better note, tethered rubber objective covers for the Type 4 804 and 820 Audubons are made by Eagle Optics and sold by them as well as B&H. They are very similar to Swaro covers and work great!
Regards to all,
ED