The only review of them that I have seen is in thread 11 here:
http://www.birdforum.net/showthread.php?t=99815
Bob
Thanks for the link, Bob.
From that thread:
I first tried zoom binoculars about 40 years ago. (I forget the brand). I thought they were actually fairly good, and really thought zoom was a neat and potentially useful feature. I have been disappointed that more progress has not been made along these lines, and am hoping that Leupold will succeed in bringing this into the mainstream. These are not technically zoom binoculars of course, but the effect is almost the same.
Precisely!
I think the typical initial response is the birder reflex that "zoom bins are bad". Well, they are. But these aren't zoom bins, AFAICT. Zoom bins use a zoom lens in the eyepiece so all the zoom lens compromises come along with it including size, weight, poor(er) AFOV and poor eye relief.
I suspect Leupold are inserting a Barlow Lens (or similar divergent) optical assembly
http://en.wikipedia.org/wiki/Barlow_lens
to increase the effective focal length of the objective keeping the same (non-zoom) eyepiece. Another route is the switch replaces a + (convergent) lens assembly with a - (divergent) lens assembly but keeping the focal point the same. I suspect the former would be "cleaner" at low magnification (which would be most used) and so might be preferred. Though I'm pretty sure it's not quite that simple given both the objective and the eyepiece are in fixed positions
Or perhaps they're adding a teleconverter.
http://en.wikipedia.org/wiki/Teleconverter
Or perhaps they are modifying the eyepiece slightly - the specs do say the eye relief changes. Not by a lot but by 3mm.
This gets rid of all the regular zoom eyepiece issues and the problem comes down to how do you do this reliably without adding too much weight or compromising other features (CA, acuity, sharpness, contrast, stray light, ... it is at least two probably more glass-air transitions though good multi-layer coatings make this possible today).
The product seems to match how users actually use the product too. Most of the time at low mag but on those occasions that need it (is that a eyering?) they can use the higher magnification.
I suspect they might sell more (or even have people experiment with them) if they tried this in a lower price point glass (say $500, as many people seem to have that as an upper bound) then migrate it up. Of course there would be some compromises (e.g. perhaps I would expect something like a Katmai or Mohave class bin).
Still it's nice to see them innovate at any price point.
One other issue I guess is that bin buyers are even less technical than other hobbies I'm involved in (e.g. amateur radio, astronomy) where the internal details of the designs of products are discussed in technical detail, admittedly by a small minority. With bins the internal designs (and design issues) are never revealed so people don't talk about the design and it's compromises directly. The reviewing is either by precise measurement (by a few) or by "black box" testing (looking through it and describing the outcome of various ad hoc tests, or, in the worst case, by just listing specs.
This state of affairs reminds me of amateur radio in the 1960s and 1970s where fashions and biases ruled the roost and important parameters (strong signal behavior) were ignored for pointless increases in sensitivity. When hams started looking for better strong signal behavior the manufacturers started to respond and build better radios.
OK, enough rambling ... need to write the rest of that review.