Brightness of image: The objective lenses of pocket binoculars are considerably smaller than the size of ordinary binoculars, and smaller than many compact binoculars as well – usually 20-25mm in diameter. The smaller the lenses, the less light that enters through the lenses. This is of no concern in bright daylight, but when looking at something in the shade of a tree, or in dim light, you will end up with a less vivid image as would be the case in ordinary binoculars with objective lenses double their size. This makes it imperative that you choose a pocket binocular with as good optic features as you can afford. The coatings should be fully multi-coated, like in the case of the Pentax 62593 8×25 DCF SW Binocular.
Field of view (FOV): FOV is the width of the view at the particular distance, e.g. 380ft. at 1000 yds. The wider the FOV, the easier to find objects and follow moving objects. Since both the diameter of the objective lenses (aperture) and the magnification play a role in determining the FOV of a binocular, pocket binoculars normally have a smaller FOV’s (smaller apertures). If you insist on the same FOV as your big binoculars, you will have to settle for a less powerful (lower magnification) binocular. The higher the magnification of your pocket binocular, or/and the smaller the aperture, the narrower the field of view. However, it has to be noted that the FOV is mainly determined by the optical design of the eyepieces. A narrower FOV is not the end of the world, but it is handy when viewing moving objects.
Good optical design can save the day for pocket binoculars as far as FOV is concerned, as illustrated in the following examples: The KOWA 8×25 Roof Prism Wateproof Binoculars has a FOV of 331 feet and the Weaver Classic 8X24 Binoculars has a FOV of 315 feet. This compares favourably with the 330 feet FOV of an ordinary size Nikon 7294 Monarch ATB 8×42 Binocular.