Lenses are such an interesting topic, a holdout that resists what has in general been a march of progress in manufacturing ability.
I'm still blown away today by the choices in lithography methods used in patterning silicon. Because large high-quality lenses get so expensive and difficult to manufacture, we have adopted rigs with systems of stepper motors to move about the wafer and lens, so that we can use both a smaller lens, and a slit (instead of annular) lens. I always think, "how can that be both easier and cheaper!", but it is...
I'm still blown away today by the choices in lithography methods used in patterning silicon. Because large high-quality lenses get so expensive and difficult to manufacture, we have adopted rigs with systems of stepper motors to move about the wafer and lens, so that we can use both a smaller lens, and a slit (instead of annular) lens. I always think, "how can that be both easier and cheaper!", but it is...
Visual aid to illustrate a "scanner" method: http://www.lithoguru.com/images/lithobasics_clip_image012.gi...
The "scanner" method is the slit lens, the "stepper" method is the smaller lens, and today we do both.
More info:
http://www.lithoguru.com/scientist/lithobasics.html
http://en.wikipedia.org/wiki/Stepper#Scanners