Gear Review: Top Mammal-Watching Binoculars

About a month ago, Jon posted a gear review of the Swarovski EL 8.5×42 binoculars. I thought I would complement his review with some remarks regarding what I think are the two other top binoculars for mammal-watching, the Leica Noctivid 8×42 and the Zeiss Victory SF T* 8×42. I have quite a bit of practical experience with top-end roof prism binoculars, having owned nine pairs from three manufacturers, and my career was spent as a research scientist specializing in image quality, including optics, so one might hope that I could find something useful to say on this topic (but no guarantees). The 10×42 analog of the Zeiss model above is my current binocular, chosen more for birding.

Let me start with a few comments regarding my choice of the top three mammal-watching binoculars. An overwhelming percentage of serious birders use roof prism binoculars made by Zeiss, Leica, or Swarovski, with 8×32, 8×42 (or 8.5×42), and 10×42 being by far the most popular options. As review, the first number is the magnification, and the second the diameter of the objective lens in mm. The ratio gives the diameter of the exit pupil, e.g., 42/8 = 5.25 mm. Brightness varies with the square of the exit pupil, and ideally the exit pupil should be larger than the pupil of the human eye (to fill it and leave some margin for error in alignment). Because much mammal-watching is at night, where there is little light and the human pupil is dilated because of dark adaptation, exit pupil size is even more critical than in birding. Therefore, I believe that the 8×42 or 8.5×42 options are best for mammal-watching, and so I selected from this category the top of the line in each of the three brands, yielding the three models mentioned.

I strongly recommend that anyone planning on purchasing one of these binoculars read the excellent review article by Michael and Diane Porter of birdwatching.com (link).  Although the review actually compares the 10x models, essentially every comment and nearly every number given in the tables of comparisons are equally valid for the 8x or 8.5x models, the most notable exception being the field of view values, which I’ll give below. There are actually far more similarities between these binoculars than differences, and all exhibit superb and nearly indistinguishable image quality, so the choice between them comes down to a relatively small number of factors, often related to usability. None of these binoculars have any significant negative issue, as far as I know. Notably, all three have outstanding eye relief (maximum eye to eyepiece distance without degradation), so the full field of view can be seen while wearing eye glasses. (An eye relief of 14 mm is inadequate, whereas 16 mm is marginal; these binoculars have 18 mm (Zeiss) to 20 mm (Swarovski), which are excellent.) As the linked review covers the features and performance in detail, I will just highlight those characteristic that I feel distinguish the three models and that I believe are important in mammal-watching.

Characteristics differing more or less significantly between these models include field of view, focusing speed, weight and balance, length, close focus distance, and straps, which I will consider in turn.

• The fields of view in feet, at a distance of 1000 yards, are 444 (Zeiss), 405 (Swarovski), and 399 (Leica). Field of view is important in scanning, and in keeping track of rapidly moving subjects, and the ca. 10% wider field of view of the Zeiss design is a noticeable advantage.
• Historically, focus speed has increased in the order Swarovski – Leica – Zeiss, and these models follow that pattern according to measurements made by the Porters. They found the Zeiss to focus about 25% faster than the Leica, and about 50% faster than the Swarovski. For an application like astronomy, a slow focus speed, allowing ultra-precise focusing, is desirable. But for mammals and birds that may be in view only briefly, I believe that the fastest possible focus speed that does not result in frequent overshooting, is preferable. There is some element of personal preference in this regard, but in my opinion, the Zeiss focus speed is ideal, and the Swarovski is distinctly slower than is optimal.
• The weights of the three binoculars are 27.5 oz. (Zeiss), 29.8 oz. (Swarovski), and 30.3 oz. (Leica). I do not have the three models available for direct comparison, but the Porters and others have noted that the center of gravity of the Zeiss binoculars is closer to the eyepieces than in the other models, improving stability and reducing fatigue (as there is less weight sticking out in front of the hands). This is plausible as the Zeiss design shifts some of the optical complexity (and thus amount of glass) from the objective lens groups to the eyepieces.
• Interestingly, the trend in the lengths of the binoculars is opposite that of the weights: 5.9” (Leica), 6.3” (Swarovski), and 6.8” (Zeiss). These are all large enough binoculars for even those with large hands to grip comfortably, so I think shorter is preferred — I’d be very happy if my Zeiss were nearly an inch shorter, like the Leicas!
• The close focus distances, as measured by the Porters, are 5.0 ft. (Swarovski), 5.4 ft. (Zeiss), and 6.2 ft. (Leica). These are all good numbers and probably sufficient for mammal-watching, though if you spend much time looking at butterflies and/or odonates, or using your binoculars for botanizing (e.g., studying arctic flowers at your feet, without crawling around on all fours), there’s actually quite a difference between the Swarovski and Leica positions.
• The strap arrangement of the Swarovskis has been very carefully thought out and looks significantly advantaged, in terms of ease of adjusting length and removing/installing the strap.

These binoculars are all decidedly better than anything available one decade ago, and I think anyone purchasing any of the three would be thrilled with their performance (unless 42 mm objective binoculars were just too large and heavy for them, in which case, Swarovski EL 8×32 or Zeiss Victory FL 8×32 models would be the top choices). That said, my personal opinion is that the Zeiss 8×42 slightly edges out the others, particularly because of focus speed, field of view, and weight/balance.

Brian W. Keelan (keelan@warpmail.net)