This is a must for any pair of birding or hunting binoculars!  Less so if your binoculars will be used in modest weather conditions (or indoors) such as the opera or a baseball game.  Birding & Hunting binoculars may be exposed to temperature swings of 30, 40, 50 degrees and more.  What prevents binoculars from fogging internally is gas sealing or waterproofing.  Waterproofing is achieved by purging the binoculars with dry nitrogen or similar gases and then "O" ring sealing the lenses and related adjustment mechanisms into place.   Without gas sealing, sooner or later, ALL binoculars will fog.  Nothing could be worse than hiking all morning to your favorite spot only to have your glasses fog.   Internal fogging should not be confused with external fogging or condensation.   Condensation on the outside lenses can be wiped away with your lens cleaning cloth or will even evaporate given a light breeze and a few moments.   No matter how good a deal or how much you want a given pair of binoculars; if you will be using them in poor weather (even just occasionally) and they are not waterproof--don't buy them!

Exit Pupil

Exit pupil is calculated by dividing the diameter of the objective lens by the magnification (i.e. a pair of 10x 40mm binoculars would have an exit pupil of 4--- 40 divided by 10. Why is this important?   Exit pupil becomes very important in low light conditions such as early in the morning or late in the afternoon.  As ambient light fades our pupils dilate (open up) to maximize the amount of light that we can see.  The average persons eyes will have a maximum dilation of approximately 4-5mm.  As we age our eyes do not dilate as much as a younger person, thus it's important to have our binocular transmit all the light that is available so that our eyes can see an image in poor lighting conditions.  On average the greater the exit pupil of our binoculars, the greater the likelihood that our binoculars will facilitate our eye's ability to see in poor light.   If you've ever wondered why your friends compact 10x 25mm binoculars appear so "dark".  It is because the exit pupil of the glasses are not allowing your eye to draw in as much light as they require. A 4mm exit pupil is about the minimum size needed for serious glassing--especially at first and last light and under dense wooded canopies!   

Exit pupil drives light transmission and light transmission drives how easy it is to see an object when ambient lighting is limited.  When buying a pair of glasses always be mindful of exit pupil and its importance to viewing in poor lighting conditions. 

Field of View

Field of view is the area seen through binoculars.  Typically field of view is measured in feet per 1,000 yards.  It can also be measured in degrees.  The greater the field of view the more area you see when peering through your binoculars.   A large field of view makes seeing moving objects such as birds and other animals easier.  A large field of view also makes scanning for objects a little faster.  As a rule of thumb, field of view is widest with lower magnification binoculars such as a pair of 8x 32mm binoculars and narrowest with higher magnification binoculars such as 10x 40mm binoculars.

Price Ranges

When picking a pair of binoculars we advise customers to set a price range.   Prices will vary from $250 all the way up to a couple thousand dollars.    If you need help picking a pair of binoculars that meets your needs and budget please don't hesitate to call and ask for one of our product specialists.   We do this all day.... day in and day out so we can quickly help you pinpoint your needs while working within your budget.    We currently have two lists that we have prepared for our customers, " The Top Ten Best Selling Binoculars and "The Top Selling Binoculars Under $500."  These lists should give you a feel for some of the most popular binoculars chosen by our customers.

Magnification 8x vs. 10x

Magnification, or power, is the ability to make an image appear "X" times closer than it really is.  That is, an 8x binocular will "bring in" the image 8 times closer than the naked eye and a 10x, 10 times as close and therefore bigger.  How much magnification is enough?  Well that depends on your needs and the intended subjects to be viewed.  If your primary use is in the deep woods and viewing distances are not great, the lower power will give a greater depth of field and generally a wider field of view without requiring a "large" objective lens as well (see next section).  But if you need to scan across the prairie's of the mid-west or the canyons of the Rockies, or get as close as possible to that Rufus Hummingbird that has been zipping through your back yard; the greater magnification will "reach" further bringing the subject "closer."    Too often we see customers purchase more magnification than they need.  For example a customer will be using a pair of glasses for in a heavily wooded area but can't figure why his/her 10x 40s don't seem to deliver as much as light as their buddies 8x 40s.  As reminder always remember that magnification and exit pupil work hand in hand.

Objective Lens Diameter 50mm vs. 40mm vs. 30mm

As a general rule, larger diameter binoculars have three main advantages over the smaller models: brightness, sharpness and steadiness.  The larger the lens diameter allows more light to enter the binocular, also know as "light gathering ability."  As mentioned earlier the objective lens size is one factor in determining the size of the exit pupil, and when the exit pupil is smaller than our eyes pupil the image gets washed out or dim (brightness and sharpness).  Also, a smaller diameter affects how much detail we can see.  It doesn't really matter if an object  is magnified 8 times if you can't see it clearly.  In general, resolution (sharpness) is best at the center of an objective lens and decreases at the outer edges because of curvature.  So, the bigger lenses have a larger central area (sweet spot) of resolution than smaller lenses.

As with everything in life there are trade-offs.  Larger lenses generally mean larger (more bulky) and heavier binoculars.  Additional weight, up to a point, can aid in the user be able to hold the binoculars steady, but if you are carrying everything you need for a long hike (and it is all on your back) every ounce can be critical. Beyond a certain point, larger binoculars become too heavy and bulky to carry easily and binoculars above 12x-50 mm are best used in conjunction with a tripod. 

Objective lens diameter can be a critical consideration in choosing a set of binoculars, but magnification, size/weight and viewing light conditions will all factor into the equation.  If your needs are light transmission (brightness) go with a lower magnification and a larger objective lens.  If you need to see further, it's more magnification and the biggest objective lens your situation will allow, keeping in mind size/weight, etc.

As in everything else, it is important to remember that there are always trade offs in deciding between  30mm's vs. 40mm's vs. 50mm's binoculars.

Terrain

Terrain can be an important consideration in picking a pair of binoculars.   If your terrain normally encompasses wide open spaces and your viewing distances are quite a large; a pair of 10x or greater binoculars should be considered.  If on the other hand you will be using your glasses in a mix of open terrain and heavy cover then you should consider a less powerful set of binoculars such as 8x binoculars.   In considering your terrain always be mindful of whether or not weight is important.  For example an average pair of 50mm binoculars will weigh 10-12 ounces more than a pair of 40mm binoculars.   If you've ever hiked along at 6,000 feet or higher; every ounce becomes critical especially as the week wears on.   

On a similar note, using your glasses in dense growth or under a heavy canopy of trees means you should consider using lower magnifications such as 8x or less.  In this type of scenario a good pair of 7x or 8x 42mm's will offer a large field of view and better light transmission.   Too often we hear of customers struggling with their 10x 42mm in this situation.  Some day a manufacturer will develop a high quality and inexpensive pair of variable power binoculars.  Until that day, don't forget to consider your terrain when choosing a pair of hunting binoculars.

Compact Binoculars vs. Full Size Binoculars

Applying what you know about exit pupil and overall viewing quality;  we prefer mid to full size binoculars for most applications.    The reason being that mid to full size binoculars will normally offer an exit pupil that is larger than a typical pair of compact binoculars.   Most compact binoculars will offer exit pupils of 2.5mm to 3mm.  If your hunting or birding scenarios do not concern themselves with light transmission, then by all means consider a pair of compacts.  However, if your typical situations include viewing in low light then please consider a larger set of binoculars that will provide you with an exit pupil of at least 4mm.  The primary advantage to compact binoculars are size and weight (some fit in a pocket) but they can be more difficult to focus/adjust than other models.  An example of a pair of mid sized binoculars would be one's with a 30-35mm objective lens such as a pair 8x 32mm's while a typical pair of full sized binoculars would have an objective lens of 36mm or larger. 

Binocular Triangle

In short, always remember that in choosing a pair of binoculars there are trade-offs.   Therefore wanting the brightest binoculars may also impact the size and weight of your choice as well as your magnification.  On a similar note, wanting the most compact binoculars possible will have a direct impact on resolution, light transmission and steadiness.