Compact binoculars come in two general shapes. The different shapes are due to the type of optics that are inside the binoculars.
The first shape is rather tubular, where the eyepieces sit practically in line with the objective lenses. The image below shows this shape of binoculars, which are known as roof prism binoculars.
The second kind of binoculars have more of a rounded look, where the objective lenses are set wider than the eyepieces. These binoculars are called porro prism binoculars. The drawing at the upper right of your screen is an example of porro prism binoculars.
Of course, each type of binocular has advantages and disadvantages.
When considering compact binoculars, the roof prism type is more common. That is because roof prism binoculars can be folded to a smaller size for compact carrying. Also, they can be made lighter and smaller than the porro prism types. Just perfect for a compact design!
