Originally posted by Na Horuk Its a whole science
I agree with most of what you have said, but - with all due respect - not this one. I should say lens making is an
ART!
It is more like cooking: You know the basic ingredients for a certain meal, but one chef makes it differently from another and results are never quite the same.
Just to illustrate Na Horuk's points about lens designs, I have attached two lens diagrams (FA 50mm f/1.4 and Tamron 01B 24mm f/2.5). It is quite obvious that even "simple primes" aren't that simple after all.
One may note that the entrance pupil of the FA 50mm is 36mm in diameter while the Tamron 24mm has an entrance pupil of 9.6 mm even though the TAMRON has a filter thread of 55 mm while the PENTAX has a "mere" 49mm. See attached photo.
Generally speaking: Making VERY large lenses is costly because it is difficult to cast large specimens without flaws. Making small may be cheap in glass but very demanding in respect of shaping and associated tolerances required.