advantages of using a convex aspherical surface for a +4.00D lens instead of a traditional surface
advantages of using a convex aspherical surface for a +4.00D lens instead of a traditional surface
The only advantage is that it would appear thinner in certain situations. At least that is my understanding. There would also be a number of disadvantages.
Question would be why? Convex for a +4.00D would mean straying from a correct curve lens, meaning dropping the BC to a +2 or flatter. Field of vision would be compromised, and even aspherical surfacing would not overcome that.
The only time I ever used a convex curve on a +4.00 was for bonded dive mask lenses, and since those were for near field for underwater use, VA was not a major concern.
It (asphericity) allows the use of flatter than best form base curves without introducing oblique astigmatism, resulting in significantly reduced lens/plate height (about 25%), reduced vertex distance, and less magnification (about 10%). There will also be some reduction in thickness and weight, usually not more than 5%.
Hope this helps,
Robert Martellaro
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Not necessarily, look at some of the newer Autograph stuff, zeiss stuff, seiko and probably hoya also (no experience personally) I edged an auto PAL with a frontside nominal base of 4.25 and a total power in the near zone of +5.75.
Happy Thanksgiving my fellow framebenders.
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