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The Binocular Advisor

The Scopes Advisor

The Tripod Advisor

High-end Scopes Review

For Bird Watcher's Digest, November, 2009

by Michael and Diane Porter

Best Resolution

A primary consideration of a scope is its resolution, the ability to show fine detail. We tested all the scopes for resolution at a mid-range distance of 25 yards. We set the eyepieces to the highest power they all had in common, which was 50x. Our target was the T-21-RP USAF 1951 resolution chart from Applied Image Inc., comprised of progressively smaller three-line groups labeled in cycles per mm. We then mapped the observed relative scores to a scale in which the top score was 5.

For scopes that got similar scores, we went further. We put a booster on the eyepieces and compared them at double magnification, at 100x. Only then could we see any differences in resolution between some of the top scopes. We also placed a one-dollar bill next to the chart so we could compare text, graphics, and fine engraving details to help distinguish between two scopes.

Vortex Razor
Copyright 2009 Michael & Diane Porter

The Kowa Prominar TSN-883 stood out. Each time we tested, the Kowa's better resolution was clearly visible even without a booster. It quickly became our reference scope, the one we kept going back to while testing, to rule out inconsistency due to eye fatigue or the effect of changing light conditions. If the Kowa's score stayed the same, we knew we could trust our eyes.

This scope raises the bar for spotting scopes to a new level. In our resolution tests, it surpassed every other top scope on the market in resolution.

For years, the Zeiss Diascope had bested every other scope we'd ever tested. Its resolution was so sharp that it beat out even the fabled 3.5 inch Questar in our tests at 60 power.

But optical evolution marches on, and the 88mm Kowa Prominar is now king of the hill.

How good is it?

We took the Kowa outside where we could look down at the pond. It was a fine summer afternoon. We immediately saw there was a bird perched in a willow tree beside the water.

We aimed the Kowa on the bird and saw that it was an eastern kingbird, with something in its beak. We cranked the zoom up to 60x and could easily identify the bug as a cicada, with its blunt-headed shape. The kingbird kept beating the cicada against a branch, softening it up to get it ready to eat.

We adjusted the Kowa's sensitive fine focus knob, until the image popped into sharpest focus. Wow! Suddenly we realized that we could even see the details of the veins in the transparent wings of the cicada.

Michael went and got his laser rangefinder and measured the distance to the willow tree. It was 80 yards away.

Kowa Prominar
Copyright 2009 Michael & Diane Porter

Why is the Kowa so good?

The 88mm objective lens contributes significantly to the amazing resolution of this scope. A bigger lens takes in more light and theoretically can resolve finer detail. The downside of a larger lens is usually greater expense and weight. Kowa, however, has held the weight of the scope plus 20-60x eyepiece to a modest 64.5 ounces. But the Prominar certainly is not the most expensive scope you can buy.

Another factor in the 88mm Prominar's good resolution performance is a pure fluorite crystal element in the objective lens. This improves light transmission and contrast and largely eliminates chromatic aberration. It is not a coating, and it is not fluoride ions in the glass. The lens element is made from industrially grown fluorite crystal.


Kowa knobsErgonomically, the scope has much to recommend it. Two-speed focus knobs allow for fast or fine focusing. The fast knob is fast. It takes only three finger swipes to go from close to far. Nothing has a good, faster focus knob.

The fine focus is very smooth and delicate, with no slack. The fast focus knob has a bit of slack, but it is smooth except at the initiation of the turn. It's big enough that you can easily run it fast with the underside of your straightened finger—a good feature when you want to go from close to far in short order, especially if wearing gloves.

KowaThe finish work and the design details are good. The eyepiece locks into place with a button on the left side. The rubber eyepiece twists out with three indents for differing degrees of eye relief. The extendible lens hood has a smooth, easy-to-use action. There is a sight on the hood for aiming.

The scope looks sturdy and feels like it has excellent build quality. It has a green, textured metallic finish.

The Kowa Prominar 883 is the angled version of the 88mm scope. There's also a straight-through version.

The similar, smaller Kowa Prominar 773 has the same design, but it has a 77mm objective lens, with HD glass rather than fluorite crystal. There is also a straight-through 77mm Prominar.

Comparing the Kowa's optical quality to its peers

It's worth noting that the next-highest-scoring five scopes on resolution — Zeiss, Leica, Swarovski, Vortex, and the 77mm Kowa — scored so close to each other that it required 100x magnification to rank them. We believe that the resolution differences between these scopes would not often be discernible in the field. But it's nice to know you have the sharpest spotting scope in the world.


Here is the Kowa warranty, as sent to Birdwatching Dot Com by Kowa on Sept. 11, 2012. Warranty

See price

Copyright 2010 by Michael and Diane Porter.

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