What difference do various kinds of prisms make?
The prism in binoculars inverts the image so that the viewer sees everything upright, instead of upside down. Roof and porro prisms perform the same function, but the roof design usually cements the prisms together, while the porro design often has the two prisms placed separately. Because of this, the porro design can re-create truer 3-D images, while the roof design allows for slimmer binoculars, and is less susceptible to misalignment due to jolting or damage.
