Tinman, ...And why are your TM 2000 lens prices so expensive?
The Tinman Respondeth:
Sir,
The glass is made in small runs in platinum-lined ovens. Precision is necessary to prevent flaws from a glass inherently unstable, as seeds, flaws, and other nasties await.
The glass is made in ingots or slabs which are then ground down to the necessary dimensions. Cheaper glass is floated in thin sheets, cut, and then ground.
Also, think of our requirements: Precise bandpass to limit color transmittance, accurate shading and impact resistance, accurately limited blue, infra red, and ultraviolet light transmittances, with nice clarity and correct size. Not the $5 smoked glass filter plates from the local hardware store's welding supply, but still a rather nice product!
