The Optical Tripod - Magnification, Brightness and Resolution

Magnification (how close it makes things appear)
Resolution (sharpness and clarity)
Brightness (called light transmission)

Ignoring a single leg of the tripod at the expense of the others erodes a binocular's optical quality and your enjoyment of them.  Powerful binoculars are useless if the image is dim or fuzzy.

Magnification or Power - what the numbers mean.

Binoculars are referred to by a combination of numbers eg 7x35,  8x40  or even 20x50.  You will see these numbers imprinted on the binocular itself as shown.

The first number is the size of the binocular’s magnification or power itself.  With a 7x35 binocular the image is 7 times larger than what you see with the naked eye.

The second number refers to the diameter of the objective lens (the lens furthest from the eye and closest to the object you are looking at) in millimetres.   A larger objective lens will take in more light to enhance brightness and resolution although there are limits to the amount of light that your eye can receive.

Field of View

The Field of View (FOV) is the width of the area that you can see through the binoculars.  This is expressed in terms of how many feet wide the area you can see is at 1000 yards away.  The FOV is usually printed on the binocular - sometimes as 'x feet at 1000 yards' or sometimes as 'y degrees'.   In the latter case 1 degree approximately equals 52 feet at 1000 yards.

As a general rule the size of the field of view will decrease as magnification increases.   However FOV is dependent on many factors and higher quality binoculars will have a larger FOV than their cheaper counterparts.

The FOV can also be increased by changing the design and shape of the binocular’s lenses and these are known as “Wide Angle” binoculars 

Resolution

Resolution is a measurement of the binoculars ability to distinguish fine detail (sharpness).   Better resolution also provides more intense colour.

Resolution varies directly with the size of the objective lens (the lens furthest from the eye and closest to the object you are looking at).   All else being equal (and it rarely is) a larger objective will always deliver more detail to the eye than a smaller objective lens regardless of the magnification.

In fact,  actual resolution hinges on  variety of factors: the quality of the optical components, light transmission through the binoculars, existing atmospheric conditions (eg heat haze), optical and mechanical alignment (called collimation - please don’t drop binoculars) and the visual acuity of the user (your eyesight).

Brightness

The size of the objective lenses determines the amount of light that the binocular takes in to send to your eye.   This in turn largely determines the brightness of the image that you see.   The larger the objective lens,  the greater the brightness and the resolving power (sharpness) of the binocular and of the image seen through the binocular.

It follows then,  that a binocular with a large objective lens is best for light conditions such as late afternoons,  overcast days and astronomy (star gazing).

Optical Coatings and Brightness

Brightness can also be improved through the use of optical coatings and Tasco use a variety and combination of coatings to produce binoculars suited for all situations:

• Coated: selected lens and prism surfaces are coated to improve light transmission.
   

• Fully Coated: all air to glass surfaces are coated.
   

• Multi-Coated: One or more surfaces of one or more lenses have been coated with multiple films.
   

• Fully Multi-Coated: all air-to-glass surfaces have been multi-coated.
   

• Rubicon tm (Ruby) Coated:  Unique to TASCO our Rubicon coating consists of 14 layers of varying colours and composition on the objective lenses. Because of their ability to filter out uncomfortable red light and provide brilliant daylight viewing,  this is especially suited to binoculars being used to view objects over water, snow or other bright conditions.
   

• UVC (ultraviolet) Coated: Removes the glare resulting from excess ultra-violet rays in the atmosphere providing a clearer more vivid image especially in brilliant sunlight.