04-22-2016, 09:54 AM
True, but it's as well an exponential degree of complexity. So we already have very complex aspherical elements plus a little ballet of linear drives to move all those elements, and all of that with their own tolerances. Multiplied by the camera's AF module tolerances (or CDAF-abilities). And all within a very small housing.
I was also thinking about an optical bench to set up those glass elements with the linear drives - but what could they do better?
After thinking again, I believe it's a matter of costs. USM need a kind of thread to move the focus element. This thread can be used for manual focus as well.
LEMs are direct. A coil and a magnet. The guidance of the focus element is comparatively cheap, two columns and two bushes. I guess, LEMs are cheaper to integrate and produce. But they come necessarily at the disadvantage of "manual focus only by wire" - as soon as they are no longer powered, you can't focus anymore. On a bellows, you don't need either.
I was also thinking about an optical bench to set up those glass elements with the linear drives - but what could they do better?
After thinking again, I believe it's a matter of costs. USM need a kind of thread to move the focus element. This thread can be used for manual focus as well.
LEMs are direct. A coil and a magnet. The guidance of the focus element is comparatively cheap, two columns and two bushes. I guess, LEMs are cheaper to integrate and produce. But they come necessarily at the disadvantage of "manual focus only by wire" - as soon as they are no longer powered, you can't focus anymore. On a bellows, you don't need either.