Glass Molded GMO Lens Elements

[JohnLo]

A general question. More and more aspherical lens elements are glass molded where they come out of the mold ready to be installed. Is glass molding being used more and more for "regular" spherical elements? For example, how many of the elements in the high volume 18-55 EF-S lens are molded? Will grinding fade away as the molding techniques get better and better?

[ebiggs1]

My understanding of this is it is simply a resin (plastic) that is molded over a ground glass lens element. Not a completed lens by itself. It is designed to do certain corrections. I admit I am not a person that is up on this topic maybe a more knowledgeable person will chime in.

[JohnLo]

The lens you describe with a resin deposited on glass is a "replicated" lens. As an example, the EF 16-35mm f/2.8L II is described as having one ground and polished, one replicated and one GMO aspheric lenses. I am more curious as to how many spherical GMO lens elements are now being hidden in lenses. Considering the volume of lenses manufactured, I would bet in a few years all but the most expensive L lenses will have GMO glass.

[shawnphoto]

I could be wrong, but I thought all the lenses were molded then polished. Am I wrong?

[JohnLo]

I have always assumed (maybe wrong) that regular lens elements were molded to within a few thousands and then polished. GMO lenses, I believe, have molds sufficiently polished to come out finished and ready to mount. For aspherical lenses, if you had to polish the glass as a final step you would not save any time or money. I remember many years ago watching my father grind a parabolic telescope mirror starting with two flat cylindrical plates. You had to remove a lot of material.

[JohnLo]

Does any Canon technical support employee ever read these threads and respond? The question I asked is about the technical design of a Canon product. I appreciate everybody's input here but they seem to be basically speculation.

Here is the question I am asking. Example; the EF 24-105mm f/4L II IS has 17 elements which includes 4 glass molded aspheric elements. Are one or more of the other 13 elements glass molded or are they all ground and polished?

Thanks

[kvbarkley]

No, no technical folks from Canon post here. Some of the mods are very knowledgeable, but not engineers.

[kvbarkley]

My google-foo failed, but your best chance for an answer is to find a white paper on that lens.