Top 3 mistakes officers make when purchasing binoculars
An officer gets advice on three traits every officer should look for before buying a pair
Sponsored by Steiner Optics
By Sean Curtis for Police1
Although many things have changed with police work over the years, the need for good binoculars has stayed the same. Whether you are working patrol, an event at a stadium, a spotter on a sniper team, or conducting surveillance on a task force, field glasses can be a critical part of the equation. Due to the science involved behind the bending and magnification of light in these modern marvels, officers can occasionally make mistakes when purchasing them for duty. I sat down with Nate Lombard of Steiner Optics to discuss the most common ones and learn how to avoid them.
Selecting the right prism
Binoculars generally come in two varieties: porro prisms and roof prisms. The differences largely lie in the amount of times light is reflected within the binoculars before reaching the eye. These different processes inherently lend themselves to some distinct advantages and disadvantages. Lombard explained not selecting the optimal model for your particular work is a mistake you want to avoid.
Porro prisms typically give you a wider field of view, and they are a bit easier to operate. The user simply dials in the eyepieces to focus the image—the binoculars stay in focus at all distances from that point forward. This is a feature that sets Steiner Optics’ porro prisms apart from other porro prisms with a center focus.
It does not matter if you’re looking across the street or 150 yards out, the images will be in focus (depending on magnification). They are limited however with their ability to view items 20 meters and in. The advantages of roof prisms are in being more compact, and they are able to focus sharply at nearly any distance. In addition, roof prisms are able to zoom in on specific targets, like a tattoo on a subject across the street. However, this requires manual adjustment each time the user looks at objects of varying distance.
Officers needing to watch over large venues with sweeping distances would do well to select porro prism binoculars since they remain in focus once adjusted to the user’s eyes. Using roof prism binoculars to scan a crowd at a stadium could cause eye fatigue. Lombard explained that even though the user might continually adjust the sharpness of the image at varying distances, the eyes still try to focus the blurry images before them. He also explained that officers surveilling a fixed position would do well to select roof prisms for their advantages.
In addition, the roof prism is more compact and easier to conceal for officers on undercover duty or officers on patrol.
Considering size and magnification power of binoculars are typically related, officers can sometimes make the mistake of purchasing more than they need. Thinking about the application in use, law enforcement officers should be mindful of the tradeoffs that come with higher end magnification. The higher the power, you can figure the bigger the size, and heavier the weight. If that officer is mobile and conducting surveillance, then a large pair of binoculars might enable far viewing but they are heavier to carry and harder to conceal. With higher magnification, you also lessen your field of view. Lower magnification will allow for a greater field of view.
The other side of this challenge is stability. When you zoom out very far to focus on something, the picture becomes extremely sensitive to small movements. A tripod is almost required in these applications because it gives you the stability to keep your target in view.
Understanding the exit pupil
Binoculars channel light to your eye so the anatomy of our peepers often comes into play. Officers unaware of the exit pupil may purchase a product that is not optimal for their needs. Exit pupil refers to the shaft of light that leaves the eyepiece and hits your eye. Lombard explained that measured in diameter, the amount of light can be determined by dividing your objective lens with the magnification power. For instance, an 8x25 binocular is going to give you an exit pupil of 3.13 mm. This is acceptable for daytime viewing because the pupil is generally in the 2 mm to 4mm range in this lighting.
However, officers working low-light scenarios may want to consider a larger exit pupil to take advantage of the pupil’s natural widening at night. Using a 7x50 binocular will net you a 7.14 exit pupil and this is optimal because our pupils operate in the 7 mm to 8mm range at night meaning we would have the most available light and best viewing.
The difference in exit pupil sizes between these two binoculars is significant.
With all of Lombard’s tips, any officer should be able to make informed decisions about purchasing the right binocular for their assignment. Starting off with selecting the right prism is crucial since size, capability, and field of view are all mission critical. From there, selecting the right power for you objective should help with balancing viewing distance and portability. Finally, understanding the exit pupil and what it means for your available lighting will help you find the right combination for your viewing scenario.
About the author
Sean Curtis is a law enforcement professional with nearly two decades of experience, serving with SWAT, diving and swift water rescue teams in Colorado. He has also served in wildland fire, search and rescue, EMS and emergency management.