[pimpim]

Was reading PHOTOGRAPHIC CENTRAL: Pentax K3 Mk III Review Series 2 and thought about what was written:

"PLM stands for Pulse Length Modulation, or easily remembered as Pulse Motor. It's super fast, Nikon and Canon use it, and I have lenses for those mounts too. The only weakness is that the type of motor can only move so much weight before it becomes obsolete. It needs to move lightweight rear lens element for focusing."

Wouldn't this mean that with resolving power of sensors getting higher and higher, the glass elements would only get heavier and the idea of pulse motors would need to be abandoned rather sooner than later? Even more so for full frame cameras?

[Fogel70]

Was reading PHOTOGRAPHIC CENTRAL: Pentax K3 Mk III Review Series 2 and thought about what was written:



Wouldn't this mean that with resolving power of sensors getting higher and higher, the glass elements would only get heavier and the idea of pulse motors would need to be abandoned rather sooner than later? Even more so for full frame cameras?

I think it is mostly about prioritizing a different design on the lens.
Where focus is moved to the rear and using focus-by-wire manual focus, than using traditional focus for DSLR which is an focus element closer to the front and having a mechanically coupled focus ring.
I believe most lenses today (mostly mirrorless) use pulse motor type or similar motor and focus-by-wire manual focus.

[pimpim]

Thanks! What I wonder is if because the rear element need to be larger these days, to fully cover sensors that have microlenses etc, I guess also the rear elements will get heavier, more strain on the motor even for a rear element..

[Fogel70]

Thanks! What I wonder is if because the rear element need to be larger these days, to fully cover sensors that have microlenses etc, I guess also the rear elements will get heavier, more strain on the motor even for a rear element..

I do not think it is usually the rearmost element, but a lens element close to the rear. so the focusing element do not have to be that big. But the important thing is that the focus lens elements are disconnected from other mechanical parts that add mass/friction and require stronger motors to drive. Sometimes focusing is done with more than one lens element. Like on Sony FE 50/1.2 GM that use two focusing element with two motors.

You Tube

You Tube

[bdery]

Wouldn't this mean that with resolving power of sensors getting higher and higher, the glass elements would only get heavier

There is no direct and unavoidable link between resolution and total lens weight.

(and as an aside, resolution is not increasing as much year on year, i.e. the K-3 iii has only 8% more pixels than the K-3)

The focus motor needs to move only the parts of the lens used for focusing, not all the lens.

For these reasons, it's not likely to become obsolete per se.

That being said, there are other technologies which are just as good, like Sony's and Tamron's linear motors, which are both fast and excellent for tracking.