Choosing Binoculars for Birding - Birding Basics
A good pair of binoculars is essential for observing and identifying birds at a distance.
Binocular manufacturers typically list their binoculars using two numbers such as "8 x 42" or "10 x 42" or "7 x 50". The first number is the magnification power and the second is the size of the objective lens (the outer lens closest to the subject) usually in millimeters.
Things to consider when purchasing binoculars:
Price. Binoculars range in price from < $100 to over $1000. While I am sure the old saying "you get what you pay for" is true to some extent, I question whether a $1000 pair of binoculars has a $700 increase in image quality over a $300 pair of binoculars.
Magnification. Most birders use binoculars that are 8x or 10x. The higher magnification of the 10x will make the subject appear closer in the field of view, but will emphasize hand shake more than the 8x. The wider field of view of the 8x will make locating birds easier and quicker, but you might lose some of the detail observed had you used the 10x.
An 8x magnification is probably good enough for most birding, and is especially recommended for novice birders. Having the wider angle of view will help you locate the birds quicker and the lower magnification will minimize hand shake.
Brightness or light gathering abilities. In general, the larger the Objective lens (the outer lens closest to the subject) and the smaller the Magnification, the greater the light gathering abilities. For instance an 8 x 42 gathers more light than a 10 x 42 pair of binoculars.
Indirectly related to brightness is a term called "Exit Pupil", which is the circle of focused light coming out of the eyepiece. The diameter of the exit pupil can be calculated by dividing the objective lens diameter by the magnification. A 10 x 42 pair of binoculars has an exit pupil of 4.2 mm (42 divided by 10). While a 7 x 50 pair of binoculars has an exit pupil of 7.1 mm (50 divided by 7). The larger the exit pupil diameter, the brighter the image. Therefore the 7 x 50 pair of binoculars delivers a brighter image than the 10 x 42.
Another factor contributing to brightness is the type of lenses and coatings used on the binoculars. Some manufacturers offer a relative brightness rating for each particular model.
Close Focusing Distance \ Minimum Focusing Distance. Will you be focusing on birds from a short range? Will you also want to use the optics for observing butterflies? In that case a close focusing distance is desirable.
Eye Relief (very important for eye glass wearers). Eye relief, measured in millimeters, is how far back your eye can be from the eyepiece and still see the whole image. Short eye relief requires the user to press their eye up close to the eyepiece, which is difficult for someone with spectacles unless they remove them. Long eye relief could be considered from 14mm to 20mm. Somewhere between the 14mm and 17mm range is recommended for the average person who wears glasses.
Many models have turn and lock eyecups that can be set at different distances from the eyepiece.
Weight. Will you be holding the binoculars for long periods of time? What are you comfortable carrying?
Generally speaking most good "birding" binoculars are in the 8 x 42 and 10 x 42 range. There are many sites that rate/review binoculars including the Cornell Lab of Ornithology and retailers such as Amazon. I suggest you do some research on your own before purchasing.
I opted for the Nikon Monarch ATB 8 x 42 binoculars for the following reasons:
Eye Relief. 19.6mm (this is great for eye glass wearers, which I am)
Mid-range price. Less than $300
Image Quality. Nikon has a reputation for quality optics associated with their digital SLR cameras. The image quality of this particular model was rated fairly high from various reviews including Cornell's.
Close Focusing Distance. 8.2 Ft.
Field of View. Specific to determining between Nikon's 8 x 42 and 10 x 42 Monarch binoculars, I opted for the wider field of view of the 8 x 42 for uses outside of birding.
There is one very minor design flaw with the Nikon Monarch ARB 8 x 42 binoculars, the eyepiece covers do not fit snuggly. They work fine for storage within the case, but more than likely they will come off if you try to use them while carrying the binoculars on a harness or neck strap in the field.
Other than the eyepiece cover problem, these binoculars are the perfect fit for my particular needs.