Complex sentence: This formula also indicates that, for an eyepiece design with a given apparent field of view, the barrel diameter will determine the maximum focal length possible for that eyepiece, as no field stop can be larger than the barrel itself.
Split into simpler sentences: This formula also suggests that given an eyepiece design with a fixed apparent field of view, the barrel diameter will determine the maximum focal length possible for that eyepiece. Because no field stop can be larger than the barrel itself.