The features you look for in a pair of compact binoculars should be determined by its intended use. The level of magnification should be one of the main considerations. If you are going to be hunting or camping, you may want a pair of waterproof binoculars. For bird watching, lightweight binoculars may be a better choice. If you just want a pair of small binoculars that you can keep in the car or truck, durability will be important.
The first thing you may notice when looking for binoculars is a label that may appear as 8 x 50, or something similar. The first number is the magnifying power listed in diameters and the second is the diameter in millimeters of the larger, or objective, lens at the front. In this example, the magnification is expressed as the size the object would appear if it were 8 times closer. Binoculars labeled 4 x 25 would show the object as if it were positioned at 1/4th the distance from the viewer.
Small binoculars tend to have objective lenses measuring less than 35 millimeters, and the smaller lenses create a narrowed field of vision, which is how much of an area can be seen through the binoculars. The greater the magnification, the more difficult it will be to follow a moving object, and if you are viewing a race or other sporting event, a higher magnification along with the smaller lens size associated with compact binoculars may not be practical.
Binoculars use two different types of prism arrangements, the porro and the roof prism. The porro system uses two prisms that direct the light in a zigzag pattern. Binoculars of this type can be identified by looking at the placement of the front and back lenses. The roof prism, so named because it resembles the shape of a roof, allows for the smaller size needed in compact binoculars. Magnified images are often inverted, or turned upside down, and prisms correct the images so that you will see them right side up.
When choosing compact binoculars, you may want to note the exit pupil. This is the term used to describe the circle of light that you will when looking through the eyepiece. The larger the exit pupil, the easier it is to view and follow the image. In small binoculars, it is usually smaller than in full size units and can result in fatigue when used for extended periods of time.
If you belong to a group that participates in an activity like bird watching or hiking, you will already have an advantage. Talking with your friends and taking the opportunity to use the equipment will make it easier to decide what kind of compact binoculars to purchase. It is important to ask for feedback from others and to try out different kinds of binoculars, because even if they are manufactured by a reputable company, they may not be suited to your needs.