convex aspherical surface

[flor]

advantages of using a convex aspherical surface for a +4.00D lens instead of a traditional surface

[Tallboy]

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.

[lensmanmd]

advantages of using a convex aspherical surface for a +4.00D lens instead of a traditional surface

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.

[Robert Martellaro]

advantages of using a convex aspherical surface for a +4.00D lens instead of a traditional surface

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

[Kwill212]

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.

I have to assume the question means usuing a convex aspheric front surface, not a convex aspheric back surface. But it doesn't say and is a poorly worded question, unless there is other context OP didn't post.

[Tallboy]

I have to assume the question means usuing a convex aspheric front surface, not a convex aspheric back surface. But it doesn't say and is a poorly worded question, unless there is other context OP didn't post.

I thought OP was talking backsurface also

[Kwill212]

I thought OP was talking backsurface also

I did too when I first read it, but that seems like such a strange question.

[Tallboy]

I did too when I first read it, but that seems like such a strange question.

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.