I've looked pretty carefully at mine and haven't seen any construction differences in Type 4 models from the 804R (1985), which has MC optics, through the 804 HR/5 (1996), which has fully multi-coated optics. The very early Swift-Pyser HR/5 equivalent of the 804R appeared in the early 80s, and used the same MC optics. However, I seriously doubt that it differed in prism construction. Frankly, I can't see any difference in optical distortion between the specimens I own, although perceived edge performance is influenced by coating effects.
I'm just saying this to maintain historical accuracy, where possible. Of course, sample variations, or differences in condition can also influence one's conclusions. My samples, including an 820 (2000), were all serviced by Nicolas Crista, and may uniformly perform better than they did originally.
Happy Holidays,
Ed
Ed,
The two FMC 804s I sold were not the same. The first didn't have the stray light issue nor did I see the prism reflections its barrels like the second sample.
OTOH, the second sample measured higher resolution on the chart (the image scale was also larger), and it had more pincushion than the first sample.
The first sample had a bit more field curvature or astigmatism (I can't remember which) in the left EP than the right. The second sample was the same in both.
Overall, the first FMC sample had more "ease of view" like my 804 MC than did the second sample, probably due to the greater pincushion in the latter.
So each 804 FMC sample had its strong points and weak points. Why the variations, I don't know.
From comments I've read about the 804 ED, the ED sample I had wasn't as good as the two I read about on this forum. The sweet spot was smaller than the FMCs (the MC version was the best in that regard), and it was shaped like a slit (noticeably sharper on the vertical axis than the horizontal).
The 820 Audubon I bought had an obstructed path like Rick mentioned, but the degree of obstruction was different in each barrel.
The view through both MC 804s I owned looked identical. So I might have gotten lucky there. I still have one of the MC 804s. Not as sharp or bright as the FMC version, but with a noticeably wider sweet spot and very comfortable "ease of view".
I wish I had taken photos through each sample's EPs and down the barrels from the objective end to show the differences I mentioned, but at the time I didn't realize that it would be of historical importance.