Optics

Binocular basics you need to know - definitions and Q & A:

Q. What do the numbers mean in the binocular description (such as a binocular that is listed as 8 x 42)?
A. - Power: The first number listed is the magnification power of the binocular: in an 8 x 42 binocular, the power "8" means that the binocular will magnify the object being viewed to appear eight times closer than it would appear when viewed with the naked eye.  A higher powered binocular will bring you closer to the object being viewed but will also lower the light gathering capability of the binocular.  Higher light gathering ability is an important consideration when viewing objects in low light conditions such as at twilight, under overcast sky's or under dense foliage.
A. - Lens Diameter: The second number in the binocular description is the diameter in millimeters of the front lens of the binocular (also called the objective lens).  In this example of an 8 x 42 binocular, the front lens would have a diameter measuring 42 millimeters across its face. A larger lens diameter will result in higher light gathering ability.  Higher light gathering ability permits better viewing in low light conditions.

Q. What is "Field of View" and what "Field of View" do I need in binoculars?
A. - Field of View is the size or width of the viewable area through the binocular usually stated in feet at a distance of 1000 yards.  A greater magnification or power of the binocular will result in a smaller field of view.  A large field of view is desirable for viewing moving objects and/or for viewing from a moving object such as a boat or automobile.

Q. What is a binoculars "Eye Relief"?

A. – Eye Relief is the distance the binocular can be held from the eye while not diminishing the viewable area.  If you will be wearing glasses when looking through your binoculars, you will want a larger eye relief.

Q. What is a binoculars "Brightness"?

A. – Brightness is a measurement of how well the binocular is able to gather light.  It is an important consideration for viewing objects at dusk or in darkened conditions.

Q. What is a binoculars "Contrast"?

A. – Contrast is the ability of the binocular to differentiate between color levels and thus identify objects against other adjoining or background objects.  The higher the contrast, the better the ability to view small differences in an object's color or to observe an object's depth from the background area being viewed.

Q. What are binocular "Lens Coatings"?

A. – Lens Coatings are special optical coatings that are applied to the optical lenses within the binocular.  There are generally four degrees of coatings from least (worst) to most (best) as follows: coated lens, fully coated lens, multi-coated lens, and fully multi-coated lens.  The level of coating will often be reflected in the price.  Most experts would recommend that you not choose a pair of binoculars with a lens coating less than fully coated.

Q. What is a binoculars "Resolution"?

A. – Resolution is the ability of the binocular to provide a sharp image.  Resolution is dependent on a number of things including the size of the objective (or front) lens, the quality of the optics and the use of lens coatings.

Q. What is binocular "Collimation"?

A. – Collimation is the proper alignment of the optics in the binocular so that the axis of sight is not impaired.  Without proper Collimation, you may view double images or blurry images.  This is a construction detail and is most likely going to be a problem only in less expensive or damaged binoculars.