Before you decide to go ahead and purchase a ZOOM binocular, please read this bit of advice:
Noted Repair Shop Caution on Zoom Binoculars

Then you can read these various posts by some owners

Zoom binoculars (at a reasonable power/aperture ratio) would be a wonderful thing to use if some manufacturer could overcome the basic design flaws of zooms: narrow FOV, dim images, and collimation problems.

My Nikon 8-16X40 XL Zoom is the best zoom I've seen, very sharp optics almost to the edge of the 5.2* FOV (wide for a zoom). However, when comparing it back to back with other good quality binoculars at 8X, 10X, and 15X, the XL Zoom is somewhat dimmer. This may be in part due to the smaller exit pupil (e.g., 2.6mm at 15X vs. 4.6mm for a 15X70), but probably mainly due to inherent light loss of the zoom lens since they are also dimmer, though less so, at 8X and 10X.

Despite this flaw, having the ability to "dial up" the right magnification for the object you want to view is a very nice feature. I'm not sure if aspherical lens technology, better coatings, etc. could overcome the inherent design flaws of zoom bins, but if they could be designed as good or even nearly as good as fixed power bins, they would surely be the most popular bins on the market.

Until then, the Nikon XL Zoom is probably the best compromise possible. The new dual power Leica Duovids look very promising, but are very pricey and heavy for handheld use. If anyone has used one of them (8+12X42) or 10+15X50), please post a review. Thanks.

Brock

See the entire discussion at
100x zoom bino's

I have a Nikon 8-16X40 XL Zoom, and it's great for astronomy, particularly from a light polluted site where smaller exit pupils are needed to increase contrast. It's also good for birding/wildlife observation (close focus 15'). Unlike many zooms it has a fairly wide true FOV (5.2*), which translates to a 83* AFOV at 16X. Of course, the exit pupil at 16X is 2.5, so the views are a little dim at the extreme. The best views are between 10 - 14X. The XL Zooms have very sharp multicoated optics, a bit sharper than my nikon 10X35E2, but with a flatter field, and sharp almost to the very edge.

The XL Zoom weighs 30 oz., less than a 10X50 Ultraview

The XL Zooms are discontinued, but a few companies (hotbuys, for example) still sell them for just under $600.

See the entire discussion at
Anybody using zoom binos?

Check out the previous thread on zooms "Anybody using zoom binos?" started by Tom Trusock. I posted comments about my Nikon 8-16X40 XL Zooms.

I've seen other zooms, and didn't like them, always cheap, dim, small FOV, and not sharp. The XLs are the exception to the rule, however, they DO suffer from miscolimation at close focus.

The alternative type of multiple power bin is the Duovid (8 + 12X42) and (10+15X50). They have two powers instead of a whole range. I haven't heard any rave reviews about them yet, but they're fairly new and VERY expensive so not many people probably have them. However, from reading about them, I think they represent a better alternative to zooms.

See the entire discussion at
Barska 12-60 X 70mm Zoom Binos

See also this thread
Zoom Binoculars for less than $150

Note these comments by various posters. The thread link follows.

note that zoom binoculars usually have a lower FOV then fixed magnifactions. They are however very helpful if these will be your main viewing tool.

Generally, zoom binoculars, although they provide a neat feature, are considered inferior to fixed mag binocs. One thing is for sure, if they go out of allignment, they are nearly impossible to get back in, even by the guys in the shops.

I've not tried the 10 -30 x 60s but although the specs may sound quite reasonable there are always severe limitations with field of view with all zooms I've tried.

See the entire discussion at this thread
Yeah, size matters... but what ELSE does?

Barska 12-36X70 zooms (mini-equipment report)