Prismatic are referred to as 6x,15; 7x,35; 7x,50; 8x,30; etc. The 6x, 7x, 8x, etc., refers to the power of the birding optics glass; namely to the extent it magnifies the object being viewed. Thus a glass of 8x makes an object in a birding optics look eight times larger than it does to the naked eye and consequently makes it appear eight times nearer. The last figure refers to the diameter of the objective lens in millimeters. The objective lens of the birding optics is the large lens farthest from the eye; the ocular lens of the birding optics is the small lens which is closest to the eye when the optics are in use.

Too many users of birding optics select their glass solely on the basis of power, believing that the higher the power the better must be the birding optics. This is by no means true. The power of the glass selected must be carefully chosen to provide exactly the right power for your special use of uses, neither too much nor too little.

Remember, the higher the power of the birding optics the smaller the field of view and the lower brilliance of the image that reaches the eye. The clarity and definition also decrease as the power increases and, most important, not only does a birding optics magnify the object being viewed but also any motion of the hand holding it and the motion of the object you are in or on such as the floor of a car, the deck of a boat, etc.

It is generally recognized, therefore, that above 8x, a birding optics glass should be used in conjuction with a rest or tripod to obtain the best results. The higher power glasses (10x and above) are only recommended for special uses such as long range game stalking, mountain scenery, etc.

This is why you will find birding optics of 6x, 7x, and 8x recommended for nine out of ten uses.