by Don Klingborg, DVM
Binoculars can be confusing and I recommend you talk with a knowledgeable person to help select the right one for you. Bev and I think they’re important on wildlife trips and add to the experience considerably. Prices range considerably and the many choices available are important to match the equipment with your needs and pocketbook. Early in our travels Bev and I tried sharing a single pair, but found we both missed too much. Now we have our own and while I use the camera more than the binoculars I still find them useful.
Binoculars are essentially two telescopes placed side by side. The large lens at the end is the collection objective and focuses the image while collecting the light (larger = better in poor lighting situations). There is a prism system housed inside the body of the binocular that flips the image so it will be right side up for the viewer. The third component in the binocular is the eyepiece objective, which actually provides the magnification.
The two types of binoculars on the market use different prism systems. The right angle Porro system is the one we envision when we think of binoculars and it creates the traditional jog in the binocular body and takes more space.
The Roof prism system requires more complex technology to manufacture, and is smaller allowing it to be housed in a straight tube body so it is more compact and lighter. The major disadvantage of the Porro system is they result in larger and heavier binoculars. Porro binoculars are said to provide better contrast and are cheaper.
Binoculars are described using two numbers -- the first number represents the amount of magnification (provided by the eyepiece) and most common choices are from 8X to 15X. Bev and currently have 10X binoculars but she also loved her 8X set (she wore it out) because it was small and light. I find 10X to be fine, but if you’re avid birders you may want more magnification).
The second number represents the size of the lens at the far end of the binocular, and is the collecting objective that “captures” light – larger is better in low light situations and is also heavier. Not a problem on safari’s as you’re riding around, but may be a problem if you’re a hiker.
Bev and I currently each have 10 x 32 (Roof) binoculars from different manufacturers and with different prices
Regardless of the system you purchase be sure they have special coatings on their lenses to minimize glare and halos of light (I’m told BAK-4 glass is the best but you’ll want to dialogue with someone with more knowledge about this).
Other factors that impact the binocular experience (and pricing) include: resolution (sharpness); brightness; contrast; color accuracy; width of field of view; percentage of the image visible if you wear glasses; ergonomics (fit and feel; weight; and smoothness of focus.
Resolution is extremely important, with more expensive lenses better at being sharp from edge to edge while less expensive lenses are sharp only in the center of the field of view. Unfortunately, the resolution of our eyes degenerates with time, suggesting the need for more quality binoculars as we age (the good news is we can give the old cheaper ones to our kids guilt free! Our kids argue that since our eyes are bad it would be a waste for us to use the good binoculars).
Eye relief is an important issue especially for those of us that wear glasses—8 is reported to be better than 10 and 42 better than 32 for people with glasses (but then I successfully use a 10 x 32 with my glasses).
Do be sure to get binoculars that can be focused smoothly with one finger.
The latest innovation brings image stabilization to binoculars. Cost and weight go up, eyestrain goes down and images improve. Many think it’s most important if you’re magnifying at 12 or higher, but some report benefits as low as 8. They do require batteries, but they still work (just not as well) if the batteries go dead. You’ll want to read more on the subject if you’re thinking about it.
Full Size (Common Specs 8 X 42 & 10 X 50)
For serious wildlife viewing and in boats. Large & considered too heavy for backpacking)
Mid-Size (Common Specs 7 X 35, 10 X 32)
Good all-around choice for wildlife & sports use. A bit heavy for backpacking, they provide above average light transmission
Compact (Common Specs 8 X 25, 10 X 25)
Best for daytime activities, eye fatigue may be a problem with greater prolonged use
The number reflects the increase in size of the subject. 40 feet away will look like it’s 5 feet away with an 8X, and 4 feet away with a 10X
Lens Objective Diameter
The second number used to describe binoculars, this is the diameter in mm of the lens at the front of the binoculars (farthest from your eyes). The
larger the objective the more light is captured and the brighter is the image, more important at dawn and dusk than midday.
This number is an indicator of how bright a subject will appear when viewed in low light situations. Higher numbers mean brighter subjects.
The number is calculated by dividing your objective (far lens) by the magnification (eyepiece).
A 20 X 32 = 32/10 – 3.2
A 10 X 42 = 42/10 = 4.2
A 10 X 50 = 50/10 = 5.0
In low light the normal human pupil can dilate up to 7 mm, so if your number is lower than 7 you’re limiting the amount of light available to your eyes. For night use may select 7 X 35, providing 5.0 exit pupil scores in a lighter and smaller binocular than the 10 X 50 (with a similar exit pupil score.
For those of you wondering, in daylight viewing the human pupil narrow to roughly 2 mm and all binoculars have exit pupil scores larger than 2 mm so no light restriction exists.
Another calculation, this time taking your exit pupil score and squaring it.
Using the three examples above an exit pupil score of 5 = relative brightness of 25 (5 X 5). 4.2 = 17.6 and 3. 2 = 10.2. Higher scores are brighter. Note that manufacturers offer that not all identical scores deliver equal brightness as prism type, lens elements, component quality and optical coatings impact the final experience.
This is associated with the distance between the eyepiece and your eyes while the whole field of view is visible. Long eye relief increases comfort by allowing you to hold the binoculars away from your face. This is most important if you wear glasses. Those of us wearing glasses should look for eye relief numbers of 11 mm or more.
Field of View
This is the width of the area that you can see at a distance of 1,000 yards from where you’re standing. Wide fields of view are best as they make it easier to find the critter you want to look at more closely, and to follow animals on the move. In general, the higher the magnification the less field of view you’ll experience.
Most binoculars offer two ways to focus:
The first is the diopter adjustment on the eyepiece (either left or right) that allows you to compensate for different sight in each eye. The second is a central turning wheel that alters the vision in both barrels at the same time.
Type of Prism
This is the element that flips the image so everything you see isn’t upside down. The Porro vs. Roof systems reflect the two kinds of prisms.
When light hits the objective some of the light is reflected away, lowering the amount of light transmission to your eyes and negatively impacting the brightness of the subject. Added coatings can reduce this reflection and help make the image sharper.
Added elements that result in a better seal from water and dust from entering your binocular. It won’t’ make them water proof so dropping them in the river will still be bad, but they do help in rain/moist situations.
Moving binoculars from cold to warm conditions, or vice versa, (just like camera lenses), may result in moisture consolidating within or on the outside of the lens. Some binoculars replace the air in the binocular with inert gas that has no moisture content so there is nothing to condense inside. You’re still responsible for keeping the outside of the lens free from moisture/dust.