The FET-300 is a fluorite ED triplet, hence it could be made at f/8. It took three years to make the objective. The fluorite and ED elements insure a very high order of color correction.

The tube is very rigid so that the objective does not deflect.

The total weight of the unit is close to 3000 lbs. Not an amateur scope.

It is a unique instrument. It should not be confused with instruments for amateurs.