by Dave Glenn
Reprinted from The Leader, Fall 1999.
Before we get into talking about a great pair of binoculars I've found let's talk about what all the numbers mean.
Optics are described by two numbers separated by an "x". The first number is the magnification (8x) or how large an object will appear when viewing through a binocular. The last number is the diameter of the objective lens in millimeters (x40mm). The objective lens is the lens nearest the object being viewed. Thus, an 8x40mm binocular will make an object appear eight times closer than the same object viewed with the naked eye and the objective lens is 40mm in diameter. When choosing an optic, higher magnification is not always better. Generally, the higher the magnification the harder an image will be to hold steady. Compact binos are also more difficult to steady than a full size. Bigger objective lenses give a wider field of view and afford more light. However, they weigh more so there's a trade off.
Exit Pupil - The amount of light exiting the binocular and entering the eye. The exit pupil is calculated by dividing the diameter of the objective lens (40mm) by the magnification (8x). So an 8x40mm binocular has an exit pupil of 5mm (40/ 8=5).
The pupil of a human eye is normally open 2.5mm but increases to 5mm at dusk. Binoculars with an exit pupil of 5mm or higher maximize the amount of light entering the eye, increasing image brightness. An 8x24mm binocular (3mm exit pupil) will perform well under normal lighting conditions where a 7x42mm binocular (6mm exit pupil) provides enough light to see during twilight conditions.
Field of View-The visible width at a given distance. Field of view may be expressed in feet at 1,000 yards, meters at 1,000 meters, or degree of angle. One degree of angle equals 52.36 feet field of view at 1,000 yards. An optic with 6.5 degrees of angle can be calculated b y multiplying 52.36 x 6.5 . . . . so it's 340 feet at 1,000 yards. Field of view will decrease when magnification is increased.
Eye Relief- The distance of the ocular lens to the point where the user's eye can see the full image (focal point) is known as "eye relief." If you wear eyeglasses and experience tunnel vision when using your binoculars, you need extended or long eye relief. Binoculars made for eyeglass wearers should offer a minimum of 18mm of eye relief. Adjustable or "pop down" eye cups can be used by both eyeglass and non-eyeglass wearers.
Coated Optics-Manufacturers apply a microscopic film of magnesium fluoride either to the prism, lens, or both to enhance light transmission. This microscopic film diminishes the reflected or stray light inside a binocular allowing more light to be transmitted to the user's eye. The more applications of this coating, the greater the reduction in glare and reflections producing a brighter, crisper, image. The least expensive process is known as a "coated" optic where only the prism is coated. "Fully coated" optics are when all lenses and prisms are coated once. The best coating available is "fully-multi coated" where all lenses and prisms are coated multiple times for the greatest amount of light transmission to the eye. More coatings mean brighter, crisper images.
Now, let's get to pair of binoculars that I've found to fit my needs extremely well. This is a pair of 8x25 compact Brunton Eterna binoculars. Why do I like them more than any other binocular I've ever had?
- Won't lose the caps. Brunton has created these lens covers that flip open at any angle and rotate 360 degrees. They even act as blinders to block out unwanted light from the sides.
- Eye Relief- Do you wear glasses or sunglasses? Ever had troubles with tunnel vision using binos while wearing them? Not with these puppies. The eye cups pull out or stay in.
- Lightweight and small (12oz) makes for comfortable hiking all day with them around your neck. Throwing them in a backpack or suitcase takes up little room.
- The neoprene bino glove: The neoprene case stays on the binos. The case keeps the dust out, and protection in. You never have to take the case off to use the binos.
- Close focus: The compact 8x24 Eternas that I've been testing have a close focus of six feet. That makes it nice when trying to decide whether that's a rufous or ruby throated hummingbird.
- Waterproof, fogproof: Nice for paddling in Southeast Alaska, birding in the tropics, or hunting November elk in the Rockies.
- Lifetime warranty: I break things. . .. a lot.
- Fully multi-coated lenses make for extremely crisp and clear images.
- 270 foot field of view @ 1,000 yards. Not bad for a pair of compact binos.
Anything I didn't like? The neoprene glove- It works great, but occasionally when I'm attempting to look through the lenses, the neoprene glove will get in the way. Brunton has remedied this by having a quick snap to remove the cover completely off of the binoculars during constant use.
Dust covers (for eye cups)- They're great, always connected to the binoculars. I haven't had a problem but a buddy of mine had a problem with the dust covers pulling off. Thank goodness for the easy replacement covered by the warranty.
Price? The compacts retail for $250 and the full size for $425.
The bottom line is they're a pair of binoculars that have exactly what I want. No other pair of binoculars that I've owned or looked at have the quality package of features that this compact pair offers. These binos offer the same or better quality as all those fancy and expensive German optics that I can't pronounce. Yes, I could purchase a pair of compacts for $70-150. ... in fact I have... several pairs. Not anymore. I'm sticking with the Bruntons.