There are two types of Sony E-mount lenses: normal E-mount lenses and full frame FE lenses. Both types can be fitted to all Sony mirrorless E-mount cameras.

The Sony FE lenses are designed for the full frame e-mount cameras which have larger sensors. These lenses will deliver an image big enough (the circle of coverage) to cover the entire large sensor. This means that when you use an FE lens on a non-full frame camera (which has a smaller sensor) it will work fine, but only the middle part of the image will be recorded on the smaller sensor. The image will appear to be "zoomed in", as though you were using a lens with a longer focal length. This cropping of the image has led to the term "crop factor", which describes the apparent change in focal length.

When you use a non-FE lens on a full frame Sony e-mount camera, the opposite problem occurs: the smaller lens is designed with a circle of coverage just big enough for the smaller sensors, and so it will not cover the full frame sensor entirely. You will therefore see vignetting around the edge of the picture where there is no image to record. You can set your full frame camera to automatically record smaller images when a non-FE mount lens is detected.