The truth about optics
The buck made his way down the edge of the food plot. One glance at his antlers and I knew exactly which buck this was. I had spent hours glassing, and all that time behind the spotting scope was about to pay off. He was with two other bucks and he was the last in line as they fed down the edge of my food plot. I let the first buck pass through my shooting lane. As soon as the second buck made it through I came to full draw and waited…antlers… head…shoulder, release. I drove a Hoyt-propelled Rocky Mountain Titanium through both lungs and the buck toppled over after a 35-yard dash.
All of the information necessary for making an ambush on this buck was gathered by glassing from a distance. There are many things to contemplate when deciding on the proper optics for a certain task. Weight, size, magnification, angle of view, light-gathering and light-transmission can all be important traits. How, when and where you plan on using your optics are all critical factors. If you are thinking about buying optics for this season, you need to read this.
Many want one binocular that will do everything. For me, I use three pieces fairly often – one, a spotting scope; two, a high power, full-size porro prism binocular; and three, a small compact binocular. You could also add a range finder and night-vision to the list.
Some compact binoculars are great for viewing in bright daylight, but during dawn or dusk they may not transmit enough light back to your pupil for suitable viewing. The objective lens size means a lot in how much light enters the binocular, but there are many other important components and features determining how much light actually reaches your eye.
With a 7x35 binocular, the "7" indicates the power. The image you view will be seven times larger than the human eye will see without the binocular. The "35" signifies the diameter of the objective lens in millimeters. All other details being equal, a 35mm lens will "seize" less light than a 50mm lens. Some binoculars will also have a third number, like 8.6, which will be the real angle of view.
To determine your "field of view," you would multiply 8.6 by 52.4. 52.4 is the linear measurement in feet that one degree represents at a thousand yards. The field of view of this binocular would be 450.6 feet at one thousand yards or 45 feet at one hundred yards.
"Exit pupil" describes the image projected to a point in space beyond the eye piece where your eye should be positioned. The relationship between the dilation or contraction of your eyes and the size of the exit pupil determines light-gathering power. A human eye pupil diameter ranges from about 2mm in bright light to about 7mm in the dark. For proper light-gathering potential, the diameter of the exit pupil must be equal to or greater than the diameter of your eye pupil during various light levels. To determine the exit pupil diameter, divide the objective lens size by the power rating. For our example of 7x35, we would divide 35mm by 7 which gives us an exit pupil size of 5mm. This binocular should give you a good exit pupil for viewing in very low-light situations, basically anything short of total darkness.
As I stated before, many other details other than the power and objective lens will ultimately determine how much light makes it through to your eye. Internal blackening, lens coatings and prism quality will also have an affect. Some manufacturers may not blacken the components inside the lens barrel. The result will be reduced image quality and annoying glare.
Lens coatings also make a big difference. All optical glass both absorbs and reflects light. The loss of light, or reflected light, affects brightness dramatically. Light transmission can be as low as 50 percent with no coating or poor coating, to as high as 95 percent with high-quality, expertly-applied multi-coating. Five percent of light absorption cannot be corrected for.
One of the most, if not the most, important components of any optical instrument is the glass. The companies manufacturing their own glass seem to shine above the rest of the industry when it comes to quality. Nikon, Ziess and Swarovski all manufacture their own glass. Using glass that is inferior quality may cause eye strain, distortion or poor light transmission.
In binoculars, you may also want to consider the difference between roof prism and porro prism. The purpose of the prisms is to correct the images you would otherwise see inverted and reversed. Roof prism binoculars are sleeker because of the straight prism tube; however, they are typically more expensive to manufacture because of the special grinding and polishing required to maintain image integrity. Porro prism binoculars are usually a little bulkier but provide increased depth-of-field for a more three-dimensional image.
Size and weight can also be important. For sitting in a treestand, I prefer a small, lightweight compact binocular. Most compact binoculars are of the roof prism design. My choice is a Nikon Travelite V, a porro prism binocular. Again, a porro prism gives you greater depth of field. If a buck is walking through thick brush it seems a porro prism "pulls" the buck out better than a roof prism design. They also have aspherical lenses which allow you to view a crystal-clear image from side to side.
If I’m on a stake-out somewhere, or on ATV or horseback, then I like to carry a Nikon 10x50 Action Extreme ATB. The large objective lenses on these binos give me superior light-gathering and resolution under any conditions. They are also waterproof, fog-proof and shockproof.
If I really need to reach out there and "count the hairs on their chin," then I use a 15-45x60 zoom spotting scope. You will not be able to "hand hold" a spotting scope because of the magnification, so I have both a window mount for use in my vehicle or a small tripod if I need to be mobile. Glassing from a distance is an important scouting tactic throughout the year for almost all game species.
One piece that is very valuable when "the moment of truth" comes near is a rangefinder. I like a Nikon Archer’s Choice Laser Range-finder. They also have a new RifleHunter 550 and Monarch Gold Laser 1200; these are the "Cadillacs" of rangefinders. However, being an archer, the Archer’s Choice is all I need and it’s a little more compact then its big brothers. Features I look for are fast display acquisition, true readings on moving targets and being able to read through clutter like grass or brush. All of these models are faultless on these features.
Whether you’re observing birds or wildlife, hiking through the mountains, watching sporting events or a plethora of other applications, different circumstances call for different optic requirements. The best environment for making comparisons is to pick out a very detailed subject in very low light. Never look through the store window where you purchase your optics. Think about what you’re going to do with your optics and pick the pair that best suits your needs.
Todd Amenrud is the Director of Public Relations, Territory Manager & Habitat Consultant for BioLogic.