Binoculars Frequently Asked Questions
June 30, 2015
Q: What is magnification?
A: 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.
Q: What is the Objective Lens?
A: 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.
Q: How do you focus your binoculars?
A: Individual eye strengths vary. Please refer to the instructions below for your individual type of binocular. CENTER FOCUS and INSTA-FOCUS?
- Adjust the interpupillary
- Set the diopter setting (normally on the right lens) to zero and view a distant object.
- Keep both eyes open at all times.
- Using a lens cover or your hand, cover the objective (front) lens of the side with the diopter setting ring.
- Using the focus adjustment, focus on the distant object being viewed.
- Cover the other objective lens and view the same object as above.
- Using the diopter setting adjustment ring, focus on the same distant object.
- 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-Focus? Binoculars do not require adjustment and use your eye's own ability to accommodate. Most users have no difficulty with these models.
Q: What is the field of view?
A: 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.
Q: What is the close focus?
A: The Close focus is the closest distance from the object that the viewer must be before they can focus the binoculars on the image.
Q: What is exit pupil?
A: 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.
Q: What is relative brightness?
A: 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.
Q: What is eye relief?
A: 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.