Humble but potential revolution: AF-P

[Akira]

Yesterday I visited Nikon Showroom in Shinjuku, Tokyo.  I tried the new 105/1.4E and found that it is a very challenging lens with the literal paper-thin DOF, especially focused at closer ranges.  Not for me, unfortunately.

I was also curious about the new AF-P lenses that employ the new step motors instead of conventional supersonic motors.  They had D5500 fitted with AF-"S" 18-55 kit lens and D3400 with AF-"P" 18-55 next to each other.  I tried them side by side, and found D3400 can focus noticeably faster than D5500 with superior AF module.  Both zooms were set at 55mm.

Another interesting finding was the noise.  The supersonic motor emits a faint squeaky high-frequency noise when actuated.  On the other hand, I couldn't hear anything from the AF-P lens.  The showroom was a bit noisy, but the noise from the AF-S lens was clearly audible, and AF-P operated totally silently.  My other experiences of the step motor was with Panasonic 20/1.7 pancake and Canon EF 40/2.8 STM.  Both emitted clearly audible wobbling noise.  The noise may also come from the focusing mechanism and not just from the motor.  But the end result of AF-P was impressive.

The recent interview to Nikon designers of 105/1.4E revealed that the supersonic motor was not power efficient: it is difficult to pull out the rotational power measure up to the supplied electric power.

Considering that Nikon traditionally employs the new technology into the entry models (Square shutter on Nikkormat FT, AE on Nikkorex, engineering plastic on EM, etc.), the literally silent and possibly more power efficient AF-P can revolutionize the auto focus function of Nikkor lenses.  That's why I mentioned the AF-P version of 50/1.8G as my Christmas present, although it was a bit too hasty.

[Roland Vink]

Very interesting Akira.

From what I understand, stepper motors have the advantage in that they can be focused (stepped) to a precise position. This is useful for contrast detect focusing in live view or mirrorless cameras: if the lens focuses past optimum point (highest contrast) it is a simple matter of stepping back again. With other AF motors (screwdriver or AFS) it is not possible to step back precisely if the target is overshot, they require a constant feedback loop - measure and focus, measure and focus - to get on target. If the AF controller can simply tell the lens to step back to where focus was optimum without needing to re-measure, focusing could be quicker.

I also understand that stepper motors are weak (so far), so can only be used to move small, lightweight elements.

Not sure if my understanding is correct though

[Akira]

Yes, the precise operation should be another important factor.

When I had my AF-S 24/1.8G calibrated at Nikon service in Ginza, the attendant explained that the calibration of the AF-S motor would be off over time, and the focusing lens unit would fail to stop at the exact position according to the submitted order from the camera.  I hope the new stepping motor will eliminate this problem.

[pluton]

The Wikipedia (or other internet) article I read about motors stated that the ring motors(variously called ultrasonic, hypersonic, silent wave, etc) are considered to be  relatively low-durability motor designs. 

[Akira]

The Wikipedia (or other internet) article I read about motors stated that the ring motors(variously called ultrasonic, hypersonic, silent wave, etc) are considered to be  relatively low-durability motor designs.

I've heard of that, too.  The friction between the two ring elements of the actuator could be the culprit?

[Bjørn Rørslett]

Whatever the underlying cause(s), ring motors are not the definition of longevity.

[ArendV]

Interesting Akira, so it is indeed not another iteration of the 18-55 but promising new technology.
Thom Hogan has similar observations in his review of the 70-300 AF-P. On top in his review of the D3400 he notices faster liveview focus with the AF-P lenses.

[Akira]

Interesting Akira, so it is indeed not another iteration of the 18-55 but promising new technology.
Thom Hogan has similar observations in his review of the 70-300 AF-P. On top in his review of the D3400 he notices faster liveview focus with the AF-P lenses.

The AF-P 18-55 has the newly designed optics in addition to the new stepping motor.  The lens barrel of AF-P is slightly slimmer and longer.  According to the MTF chart, AF-P is slightly better at the widest setting and a little inferior at the longest end.  The largest magnification factor of AF-P is higher.

[Erik Lund]

Thanks for the heads up and details.

There is a whole lot more to the design of the AF than just the type of motor. The way the lens elements are secured to the moving part of the motor or motors and guides must be very strong and stiff to prevent any unwanted movement or breakage.

I don't like the design with one linear motor on one side of the element where the element is more or less just dangling back and forth in the lens barrel,,,

By far I prefer the circular motors, they are strong and a very stable design. Despite the drawback of wear.

https://www.lensrentals.com/blog/2016/04/a-look-at-electromagnetic-focusing/

[Akira]

Erik, I share your sentiment abuot the dangling focusing element which is not very good for the mental health. 

Hope Nikon will come up to the reasonable focusing mechanism along with the wider employment of the stepping motor.

[ArendV]

Interesting Erik.
Now I know what the rattling sound was of the Sigma DN lenses (that I used to own) when powered off, a loose focusing unit 

[Erik Lund]

When power is off for some reason, for instance when the motor dies, these lenses with 'linear' motors are basically not usable since you cant focus them at all,,,

[David H. Hartman]

So what is the prognosis: are things getting better or worse?

[Erik Lund]

I feel that A lens without MF at least as a back up is worse,,,

[David H. Hartman]

I never should have sold my Nikon F.