This is the Optimus 500 Lantern, found in a military surplus store, It's of mixed generations, meaning that some parts are of an newer generation than others, in this case the fount is of a later date than the rest of the lantern. My guess would be that this lantern is from the era just after WWII to maybe early 1950's This mixing of generations is quite common when it comes to Optimus surplus lanterns, i guess the used on self parts. The glasscylinder might have been changed at sometime as it says Optimus No 300, Frederik
I'm not sure they ever made a glass where it says 500. The glass is the same size and I don't think they sold many of the 500 lanterns. The same argument could be used for the 1300 lantern. I have never seen a glass with the number 1300, only 300.