Assertion: eyepiece's length | /r/HasProperty | produced since their introduction
Facets:
value: in the early 1940s
type: TEMPORAL
Source sentences:
text: Vernonscope estimates that over one million Brandons in various incarnations and focal lengths have been produced since their introduction in the early 1940s, proving that a good design endures, while eyepiece fads and fashions come and go.