Help with understanding aspherical lenses?

[bshanahan14rulz]

Ok, so I'm trying to find an aspherical lens with matching dimensions to one I am holding in my hand. If I hold it dome up and look at something on my desk, the point at which everything gets infinitely large and then flips around is one of the focal points, but which one, A or B?

It is measured in mm. but is it mm between focal point and the flat plane? perhaps the rounded side?

and what's this about two focal points? they are on the same side, correct?

I guess my main question is this: the focal measurement is the distance between the focal point and what?


Here's something I threw together with MSPaint to help explain my question. are the focal lengths the measurements in set 1 or set 2? or something else entirely? Thanks!

[bshanahan14rulz]

bump. Is the diagram above even correct? I'm just assuming, since I figure the focal point would be where i can be on the other side of the lens and see everything get infinitely large, the spot where the image flips.