FREQUENTLY ASKED QUESTIONS
The purpose of this page is to give answers to the general questions asked about Binoculars like:
What is magnification?
What is the Objective Lens?
How do you focus your binoculars?
What is the field of view?
What is the close focus?
What is the exit pupil?
What is relative brightness?
What is eye relief?

What is magnification?
Magnification is the degree to which the object is enlarged. With a 7x35 binocular, the object will appear to be seven times closer than without the aid of a binocular. The number immediately following the "x" is the diameter in millimeters of the objective (front) lens. The larger the front lenses the more light that is allowed to enter the binocular. A 10x50 binocular has 10 times magnification with a 50mm objective lens.

What is the Objective Lens?
With a 7x42 The number immediately following the "x" is the diameter in millimeters of the objective (front) lens. The larger the front lenses the more light that is allowed to enter the binocular. A 10x50 binocular has 10 times magnification with a 50mm objective lens. This photo is showing an objective lens that is 42 millimeters.

How do you focus you binoculars?
Individual eye strengths vary. Please refer to the instructions below for your individual type of binocular. CENTER FOCUS and INSTA-FOCUSŪ 1. Adjust the interpupillary distance. 2. Set the diopter setting (normally on the right lens) to zero and view a distant object. 3. Keep both eyes open at all times. 4. Using a lens cover or your hand, cover the objective (front) lens of the side with the diopter setting ring. 5. Using the focus adjustment, focus on the distant object being viewed. 6. Cover the other objective lens and view the same object as above. 7. Using the diopter setting adjustment ring, focus on the same distant object. 8. Your binocular should now be adjusted for your eyes. Make a note of the diopter setting for future use. - Notes: Zoom Binoculars should be focused at the highest power possible. Perma-FocusŪ Binoculars do not require adjustment and use your eye's own ability to accommodate. Most users have no difficulty with these models.

What is the field of view?
The field of view is the width, measured in degrees or feet, of the viewing area you would see at 1000 yards. Field of view is generally affected by the power of the binocular compared to the objective lens size. A larger power (if the objective lens size stays constant) will lead to a reduced field of vision. A larger objective lens (if the power stays constant) will lead to a larger field of view.

What is the close focus?
The Close focus is the closest distance from the object that the viewer must be before they can focus the binoculars on the image.

What is exit pupil?
The exit pupil refers to the size of the shaft of light transmitted to the eye. The larger the exit pupil, the brighter the image will appear. The exit pupil is an important indicator of the binocular's low light performance. You can actually see the exit pupil by holding the eyepiece of the binocular approximately 12 inches from your eye. It is the bright circle of light in the center of the eyepiece. Exit pupil is expressed in millimeters and is normally derived by dividing the power into the objective lens diameter. A 7x35 binocular has an exit pupil of 5mm (35/7). A 15-power binocular with a 60mm objective lens diameter has an exit pupil of 4mm.

What is relative brightness?
The relative brightness index is used to compare how well binoculars with different size exit pupils will perform under dark conditions. This index reminds us that as the size of the exit pupil increases, its area and ability to transmit light grow geometrically. To find the relative brightness, square the exit pupil. A binocular with an exit pupil of 5mm has a relative brightness of 25 (5x5=25). Because relative brightness does not consider factors such as optical quality or coatings, it should be used only as a rough guide.

What is eye relief?
The distance between your eye and the eyepiece is called "eye relief." Extended eye relief is one of the three most critical performance factors, along with magnification and field of view, especially for those who wear eyeglasses in the field.

Use the following table to help you make the best selection:
Intended Use/Recommended Models
 
Stadium Sports
4x21, 7x32, Wide Angle Models (best for full field viewing),  7x35, 8x40. Any zoom or wide angle model (compacts would also be acceptable).
 
Boating
7x50 (for best light gathering). Any waterproof or rubber armored models are preferred. Image Stabilized binoculars.
 
Outdoor Concerts
4x21, 7x32, Extra Wide Angle, 7x35, 7x50, 8x40. Any compact, zoom or wide angle model.
 
Outdoor/Nature
7x35 Wide Angle, 7x35, 7x50, 8x40, 10x42, 10x50. Any wide angle or wide angle zoom model.
 
General Use/Vacation/Hiking
7x35, 10x50, 8x40, 10x42, compacts or any wide angle model.
 
Hunting
7x50 (for extra light gathering ability), 7x35, 8x30, 8x40, 10x50, 10x42, folding roof prism compacts or any rubber armored model. Camouflage or black versions are preferred.
 
Bird Watching
7x26, 8x36, 8x40, 7x35, 10x40, 10x50, 10x42. Binoculars with extended eye relief and close near focusing are preferred.
 
Theater/Plays/Indoors
4x21 Extra Wide Angle. Any theater glasses, compact model or general sports glass.
 
Low Light
7x50, 10x50 (for greatest light gathering).
To get to the products page click on the following links:  Digital Binoculars, Bushnell, Leupold, Nikon.