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A Look at Electromagnetic Focusing
An interesting look at electromagnetic focusing by Roger Cicala:


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I'd like to read the article but somehow it's blocked.....whatever the browser!

Dave's clichés
Interesting stuff ... we will see how long it takes until such a

linear drive is used in one of Nikons and/or Canons lenses.


Also, we'll see when one of the manufacturers takes advantage

of the newly gained ability to move single lenses or groups

entirely independant from each others.
To do what by moving independently? They have to remain depending to the other glass elements (some time ago those were called "floating elements"), because only that way they can act correcting. It might be easier to do mechanically by curves or levers. I wonder about the power consumption compared to USM drives and also the sensitivity and long time reliability.


The latest models of our high precision grinding machines also have linear motors which bring a lot more weight at the precision of a fraction of µm to the right place, repeatedly

Quote:To do what by moving independently? ..

That remains to be seen. "Traditional" lens constructions never had such an ability, hence

in a lens of today, you will not find such a construction. Eventually, the ability remains

meaningless ... eventually someone comes up with a clever idea ... it is an additional

degree of freedom to the lensconstructor.
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 like the Ring drive USM,  I've dismantled the Nikon AF-S 70-300mm VRII, because of a problem of non use of the lens, I was very pleasantly surprised to find how simple the motor is and how well it is made, using the principle of crystal's dilatation (expansion and contraction with voltage) at high frequency as a drive medium, the motor drives the focus ring itself, which in turn makes it a simple to have full time manual, power or no power..... In fact it has really very few moving parts and focuses very fast. 


  I've nothing against LEMs the principle is also simple, however it starts to make me nervous if we start finding three or four of these LEMs controlling movements, and when unpowered the fact the whole system goes limp.......four motors, giro stabilization and all the appropriate electronics......electric diaphragms......add to that lens docks for fine tuning element alignment, in plastic bodies....


.......I like the "KISS" principle......


   Keep It Simple Stupid.........


Edit.....make that KISSS....

    Keep It Simple Stupidly Solid.......and pass it on down the family.....

Dave's clichés

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