When Zeiss introduced the mid-size Victory FL binoculars, several years ago, they said this:
"Schmidt-Pechan prisms with new dielectric mirror layers as a reverse system – phase-corrected, of course, were used to economise on space and weight. Transmission of these new prisms is over 99%."
So there seems to be very little transmission advantage to Abbe-Koenig prisms. This tallies with separate claims about the efficiency of dielectric mirrors, too.
Either Abbe-Koenig prisms have another optical advantage, or their true advantage is a marketing one, or they have no advantage at all and Zeiss misjudged the market on this issue (and succeeded despite that).
However, Abbe-Koenig prisms do have one notable
disadvantage, mentioned by ronh above: they're big. You'd expect that to result in big binoculars, and the full-size Victory FLs are indeed a bit bigger than their nearest competitors.
Still, I can think of some ways to keep the overall binocular short despite using Abbe-Koenig prisms:
- Use a telephoto construction for the objective lens. That is, use a positive front component widely separated from a negative rear component (in this case the focusing element or doublet).
- Make a faster objective, i.e. of a lower f-number, like f/4 instead of f/5. This reduces the focal length for a given objective diameter. E.g. a 210 mm f/5 lens and a 168 mm f/4 lens have equal diameters (42 mm), but the latter has a shorter light path. Ronh implies Zeiss did this.
- Using a shorter focal length objective (2, above) necessitates a more elaborate ocular construction to achieve the desired magnification and eye relief. Thus this necessary sophistication is part and parcel of making a binocular simultaneously compact and practical to use.
The downside to all these techniques is that they compromise the quality of the view, particularly for off-axis subjects. And to the extent that they're nevertheless useful, they're just as applicable to binoculars with Schmidt-Pechan prisms.
The full-size Victory FL binoculars are obviously successful despite these difficulties. But to the observant, there are some signs that Zeiss struggled with these problems:
- The eye relief of around 16 mm is on the low side of generous, though Zeiss made the most of it by wasting unusually little space between the lens vertex and its mount, i.e. the last glass surface of the ocular is nearly flush with the eyecup.
- Zeiss moved to FL glass before the other alphas, presumably under pressure to offer a tangible advantage.
- In addition to FL glass in the objectives, other glasses with anomalous partial dispersion were used in the Victory FL binoculars. (I read this in a press release somewhere.) It wouldn't surprise me if special glasses were used in the ocular lens too. These glass types are generally expensive.
- Field curvature and astigmatism are present in abundance, and there's a good dose of rectilinear distortion too.
- Zeiss used a plastic body construction to keep the weight of the larger binocular manageable. This plastic wasn't met with universal approval.
- The aforementioned larger binocular size should be mentioned separately. Done!
I'm convinced the success of the Victory FL has more to do with the state of its competition (Swarovski, Leica, and Nikon could each be described as lazy a few years ago, for varying reasons) and superb design choices by Zeiss, than any inherent superiority of Abbe-Koenig prisms. The design choices I'm talking about are things like eye relief, size, materials versus weight, off-axis aberration correction, on-axis sharpness, etc. Zeiss walked a perfect tightrope with the Victory FL, making excellent judgments on what the market would accept and playing to their strengths. The designers made good use of what they had: FL glass, great coating technology, access to new plastics, a wide angle of view since a short focal length was forced by the Abbe-Koenig prisms anyway, unusually good central sharpness since low astigmatism/field curvature was always going to be tough, etc. They did a brilliant job.
But I think Zeiss will have a much harder time with the revitalised competition of Swarovision, EDG, and any eventual next-gen Leica. Banking on the trivially higher transmission of Abbe-Koenig prisms in the Victory HT doesn't bode well, in my view.
Dorian,
I'll add my kudos to the pat-on-the-back parade. I enjoyed reading your post, it had some good insights, though I can't speak to the technical suggestions you made about how to better accommodate A/K prisms; however, as you implied in your last sentence, they might be overcome by events at this point now that dielectric coatings are available on S/P prisms.
I think Zeiss getting out ahead has been what's expected from the company after its introduction of phase coatings. But we should keep in mind that even though they have made the classic roof of all times it seems, as Arthur pointed out, when you add up the number of roof models they have offered over the past three decades, it hasn't exactly been an avalanche of products like say, Nikon, which probably has had more versions of the Monarch than Zeiss has had total roof model (hyperbole, but a point well taken, I think, being that Zeiss has rode on a wave of success with just a few excellent roofs).
Zeiss initially developed its good reputation for its excellent porros, though only the 7x50 B/GAs still lives on. I've wondered which demographic/hobbyist buys these IF 7x50 porros in enough quantities as to justify continued production while other great porros from Zeiss, Nikon, B&L/Bushnell, Swift, etc. have gone the way of the dinosaur? How did this lone species survive the onslaught of the roof invasion?
Hunters? That's the group apparently sustaining the lone Zeiss ClassiC - 8x56 B/GA. I'd like to see the 7x42 B/GA resurrected and updated but would there be as many birders who would buy it as there are hunters who buy the 8x56s? I would have to guess not, or Zeiss would have already brought it back.
Zeiss took a risk making an alpha with a fiber reinforced polycarbonate body. "Lidder is bedder," but the FLs have had their share of critics because of the "plasticy" body, not just because of the feel but also a lack of confidence in its durability and robustness. What Zeiss needed was for the guys who ran over the Steiners to rip some rubber on the FLs.
I know there were complaints about the Night Owls' weight but they went from one extreme to the other. That was a bold move and despite the critics, most people seemed to accept the change over to polycarbonate once they got used to it.
Still, an FL "run over video" might have quickened the FL's acceptance, particularly in the hunting community, where "ruggedness is next to Godliness". Perhaps this might be why Zeiss went out of its way to market the HT to hunters.
The "brilliant" design choice" I have always questioned in the FL is Zeiss' postulate that you need to sacrifice edge performance to get better centerfield performance. I've never seen that claim substantiated, and as an adherer to the scientific method uber alles I'm surprised that Ed would swallow that potential malarkey without hard evidence to back it up. Yet, not a peep about that.
If a miracle occurred <here>, I might be able to afford an HT, but from what I've read so far, I don't know if I would like it even if I did hit the Power Ball.
When I first saw the photos, I really didn't know what to make of it. It was as if ZR had shrunken the double open bridge of its 7x36 ED2 into one bridge. And what about that half on, half off rubber armoring? Sort of like the EDG I.
Then again, I didn't know what to make of the original Victory, with it's odd triangular shape. It still looks a bit odd to me, but I'm already warming up to the HT body design.
After Steve Ingraham's comment about the Victory I's "rubber tire" smell and "meat hook" strap lugs," I lost some enthusiasm. Then came the reports of excessive CA, and it never made my Wish List though the 7x42 ClassiC remains on it.
It will be interesting to see if Zeiss retains the optical characteristics of the FL or goes another way. Sometimes "progress for progress sake" isn't the best path. Sometimes in moving ahead too quickly, you leave something good behind.
I'm hoping that the HT's optical design will be more like the Classic than the FLs, that is, ample sweet spot with gradual fall off at the edges and low astigmatism and just a bit of field curvature, less than the Classics.
One thing about Zeiss that you rarely see from Leica and Swarovski is some really nice discounts, not half price discounts like Nikon, but there have been some nice prices on FLs, particularly the 8x32 and 10x32 models.
If the HT does depart from the FL optical design, I think you will see some division btwn the FL crowd and the new adopters initially, and if stores offer trade-ins for HTs like they are doing for the SV ELs, I can imagine some FL owner uttering those famous words: "You'll have to pry it from my cold, dead hands!"
Well, I think we can at least be glad for one thing, alphas don't change designs every four years like automakers.
Brock
