Bias / Distortion - Binoculars
An important optical feature of binoculars is the bias/distortion factor. If you look at a tiled wall through binoculars, you expect all the straight lines of the tiles in the original wall to be straight in the image you see through the binoculars. To achieve this, the optical features of binoculars need to be both sophisticated and of superior quality. Cheaper models generally fall short in this regard.
It is good to bear in mind that many optical features demand the opposite requirements from a lens system. You will always have to compromise as there are various errors or aberrations that can occur in an optical system.
It is a matter of deciding for yourself what is important to you and what is not. For instance, a small degree of bias/distortion is far less important to a bird watcher than it is to an architect, who is constantly working with straight lines.
In the grids depicted below, you can see an example of pincushion distortion, no distortion and barrel distortion.
In the photos below (made by the computer), the same bias is applied to both the photo of the building and the photo of the cat. The distortion is clearly noticeable in the photo of the building, however, it is barely discernible in the photo of the cat. And this is precisely what happens in daily practice.
