Binoculars and Spotting Telescopes for Birders: Companion to the Executive Synopsis

by Pete Webb

This is a text intended as a clarifying companion to the executive synopsis. It explains what that extra money for higher classes of optics is actually buying, and fills in some gaps.

See the main article for the meaning of specs like field of view, eye relief, exit pupil, etc. and why they can really matter quite a bit with binoculars. Also in the main article are these spec's for some recommended models.

The manufacturers' sales literature makes much of the anti-reflective coatings on the lenses, which can help make the image brighter, but other factors also contribute to that, and the steps up in image quality among price classes are primarily due, not to the coatings, but to the types of lenses used.

The economy class uses a two-element "achromatic" lens for the objective lens, and single element lenses for the eye piece lenses. This overall grouping splits in two sub-groups, depending on type of prism used. Roof prism binoculars in this group, costing less than $90, won't measure up in performance to their porro prism counterparts; it costs money to "fix" roof prisms with a phase-correction coating on the "roof" surfaces which give them their name. So in binoculars costing under $90, the porro prism models will out-perform the roof prism models. Some of the porro prism models can cost well over $150 and still belong in this group, with single element eye piece lenses.

The group I call "mid-grade" steps up by using two-element "achromatic" lenses for the eye piece lenses in addition to the objective lens, producing a sharper, clearer image. A few binocular models with porro prisms are in this group, but the majority are sealed roof prism models (which are more durable and less heavy or bulky).

The groups I call "premium" and "elite" step up further in two ways: they use eye piece lenses with special "aspheric" curved shapes, sometimes also called "field flattener" lenses. These make the focus uniformly clear and sharp across the whole field of view. The other major step up is a THREE-element "Apochromatic" objective lens. These two expensive improvements make a noticeable improvement in clarity of small details in the image, and reduce eye strain in long periods of use. With spotting telescopes, these refinements also extend the range of the 'scopes, resolving finer details at greater distances.

The step-up from "premium" class to "elite" class optics is in the use of expensive fluoride formula glass in the lenses, making colors a bit more intense and a very small improvement in resolving tiny details. (See color dispersion in main article.)

Having said all this, one can get roughly the same view of a fairly close-by bird in good light, with a dark background behind it, using any reasonable pair of binoculars of any of these classes.

It's the more difficult lighting or tiny details on far-away birds that reveal the difference in optical quality among the different lens-type optical equipment grades. Higher-grade binoculars can still show some color on badly backlit birds or birds hidden in shadows. The higher grades also reduce eye strain with prolonged use.

With spotting telescopes, with their higher magnification, the optical flaws in the lower classes are more obvious. One can use a "mid-grade" type of telescope, as I do, and see about the same view of birds within about 50 to 75 yards, as one can get with a multi-thousand dollar elite-class 'scope. But the elite class 'scopes can show smaller field marks on birds farther away than my 'scope can resolve. And that's what a spotting telescope is for.