How To Use Central Focusing (CF) Binoculars
There are two available types of binoculars, according to how they focus: The CF (Central Focusing) and IF (Individual Focusing) binoculars. As soon as you know how to properly use binoculars, you can experience the full viewing excitement. Getting the knowledge on a few simple procedures will ensure your enjoyment.
Nomenclature of Central Focusing Binoculars – The CF binoculars comes with these features: eyepiece lens, turn and slide eyecup, neck strap eyelet, diopter adjustment ring, focusing ring, body (tube), performance indicator, objective lens.
Adjusting Eyecup (turn and slide)
If you are a non-eyeglass wearer, you should set the eyecup to the fully extended position. But for as an eyeglass wearer, eyecups should be set to the fully retracted position.
Using the eyecup in an appropriate position, looking through the binoculars from where the exit pupil is formed (eye point), the entire field of view can be obtained without vignetting.
To set the turn and slide eyecup: a non-glass wearer should turn the eyecup counterclockwise to the fully extended position. In the case of a rubber eyecup, you should set the rubber eyecup up.
As for the eyeglass wearer, he should turn the slide and turn eyecup clockwise to the fully extended position. And for the rubber eyecup it should be folded back.
Adjusting Interpupillary Distance
Interpupillary distance varies among individuals. So you need to adjust the distance of the eyepiece lenses according to your own interpupillary distance.
While looking at a distant object and holding the binoculars with both hands, carefully move the binocular tubes downward or upward until left and right fields are correctly aligned, forming a perfect circle.
The image might be uncomfortable to view if the interpupillary distance has not been properly adjusted.
Adjusting The Diopter
You need to adjust the diopter if you are to look through binoculars with both eyes. If for instance you have a different visual acuity between left and right eyes, if without doing this you look through a binocular, will not see sharp, crisp images because one eye will see objects in focus while the other does not. Coupled with the fact that you will suffer eye fatigue.
It is usually better to adjust the diopter of your left eye first, then your right eye. To do that just focus with your left eye by focusing ring. Look at an object through the left eyepiece with your left eye. Rotate the focusing ring until you see a sharp image of it.
Then coming to the rigfht eye, focus with the right eye with diopter adjustment ring on the right eyepiece. Look at the same object through the right eyepiece with your right eye. Rotate the diopter adjustment ring (usually located on the right eyepiece) until you see a sharp image.
Focus With Focusing Ring
You focus an object by rotating the focusing ring. Turn the focusing ring to focus whenever you change the object viewed, if the diopter has been adjusted.
Read also: Binoculars – The Basics