Sunday, May 5, 2019

Binoculars - The Big Picture

Binoculars – The straight goods – what to buy – how to adjust them

As trackers tend to move fast and light, the best binoculars are compact, light, and powerful. The rule of thumb is to buy the best quality that you can afford. What you are paying for is higher quality optics. This usually results in crisper focus and better low light performance.

What do the numbers mean?

Binoculars have a couple of numbers stamped or embossed on the housing. Expressed as two numbers such as 7X35 or 8X40, the first number is the magnification. So, a “7” means that the image produced is 7 times larger than what would be seen by the naked eye at that distance. Most people find that a magnification between 7X and 10X is suitable. Lower powers tend to have a larger field of view, so you see more area, whereas, higher magnifications generally have a smaller field of view. Higher magnification can also be harder to hold steady which could result in a “shaky” view. The second number indicates the size of the “objective” lenses in millimetres, (these are the bigger diameter lenses opposite the eyepieces). The larger these lenses are the more light that is gathered to form an image. Basically, the higher the second number, the brighter and the sharper the image. The down side is the larger the objective lenses, the bulkier the binoculars are and the more they cost.

How to adjust your binoculars for your vision.

To get the most out of your binoculars, lets take a couple of moments to find out how to properly adjust them for your vision thus insuring maximum performance.

Focus and adjustment

When you look at your binoculars you will notice that there are two optical tubes with a hinge in the center. On one end you will notice that the lenses are smaller than the other end. The smaller lenses are the “eyepiece” lenses that you look through. The first adjustment that you make is to bring the binoculars to your eyes and look at an object in the distance. What you see will probably be blurry and vignetted. Vignetted means that there will be a black area around what you see. To remove the vignette, move your eyes closer to the eye piece lenses and adjust the center hinge by gently spreading the optical tubes in or out until the vignette disappears.

The next step is to focus the lenses. Although some binoculars designed for heavy field use such as military applications have “independent” focus – meaning that each side can be adjusted to the user’s vision independently, most binoculars have “central” focusing.

Central focusing involves adjusting the focus of both optical tubes simultaneously by rotating the central knurled wheel - usually located in the hinge between the optical tubes. Simply roll the focus adjustment back and forth until a distant object comes into clear focus. However, as most of us have different vision in each eye, don’t be surprised if one optical tube will be in focus while the other isn’t... to check this, close one eye and adjust the focus, then close that eye and open the other and see if the focus is still clear and crisp. If it is not, you must set the binoculars up for your specific vision. To correct for this, one eyepiece is adjustable. The adjustable eyepiece is called a “diopter”.  You can tell the diopter lens as it has an adjustment ring on it with increment marks.

To adjust the diopter for your specific vision, focus the binocular on a distant object using the central focusing adjustment while keeping the eye looking through the adjustable diopter lens closed. Once clearly in focus, close the other eye and adjust the diopter lens until that eye is in focus. If done correctly, when you look through the binocular with both eyes open, your focus on a distant object will be crystal clear and crisp.

Once this adjustment has been made for your specific vision, the binoculars can be refocused on an object at a different distance by using the focusing wheel to adjust both tubes together without any further eyepiece readjustment. 

What not to buy
When shopping for a new set of binoculars it is best to avoid “focus free” or “fixed focus” binoculars or units with a zoom feature as these usually are a compromise at best. Other features like a built-in compass or a range finder are better suited for the marine or military environment that they were designed for.

The adage that “you get what you pay for” is especially correct when purchasing binoculars. For trackers, the best binoculars are compact, light, and powerful. Remember the rule of thumb is to buy the best quality that you can afford.  What you are paying for is higher quality optics. This usually results in a crisper focus and better low light performance. Consider your new binoculars a lifetime won’t be sorry going with quality.


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