[Jeff Lopez]

Was reading a post over at NikonForums, and some more, lots of D5x00and D7x00 AF issues with AF-S lenses,(couple of exPentaxians there with perceptual remorse?)
Anyway, I been thinking that if its only with Nikkors with af motors, it maybe that those motors are too torqued and actually land beyond focus, doesnt "brake" well..
Do SDM lenses have this problem?

[hyyz]

From my experience with SDM lenses, I think they have similar problem based on what you said about Nikkors. My SDM lenses all have some back and forth AF adjustments when auto focus, some are better and some are worse. But the problem is there.

[photoptimist]

Nikon AF-S uses the same motor technology as Pentax SDM and may even be using the same motors from the same supplier.

Pentax SDM lens also have some reliability issues (look up "SDM failure" here on PF) although the exact percentage of failures is hard to know given that the internet broadcasts a lot more noise about failures than about all the people that have no problems.

[Jeff Lopez]

Nikon AF-S uses the same motor technology as Pentax SDM and may even be using the same motors from the same supplier.

Pentax SDM lens also have some reliability issues (look up "SDM failure" here on PF) although the exact percentage of failures is hard to know given that the internet broadcasts a lot more noise about failures than about all the people that have no problems.

Yes, that could be a real problem..Hopefully this supplier revises their stuff, but that would based on feedback, I guess. I was about to buy a sdm lens but this is kind of scary right now..

[northcoastgreg]

I've had only two lenses with SDM motors: the DA* 300 f4 and the DA 17-70 f4. The DA* 300 is my most accurate focusing lens; the DA 17-70, on the other hand, seemed incapable of attaining accurate focusing, and would front focus at some focal lengths, back focus at others, and was immune to focusing corrections. So it really depends on which SDM motor and which lens, and possibly on which camera as well.

[starbase218]

I have a Nikon D7100 and several Nikon lenses.

There are two types of AF-S (which is also called SWM - silent wave motor): micromotor SWM, like the one in the 35/1.8, 85/1.8 and 16-85/3.5-5.6, are small motors that drive gears that in turn drive the mechanism to make the lens focus. This is very similar to the SDM motors found in e.g. the DA* series lenses and the DA 17-70.

The other type is ring-type SWM, which can be found in lenses such as the 12-24/4, 17-55/2.8 and 70-200/4 (but, surprisingly, also in the cheap 18-70/3.5-4.5). Ring-type SWM is a motor that is looks like a ring, and it sits around the aperture of the lens. It is generally very fast, faster than micromotor SWM or SDM, and provides more torque as well.

However, SDM is not always the micromotor variant either. The rebadged 15-30 and 24-70, that also carry the SDM nomenclature, actually use ring-type ultrasonic motors, just like the more expensive Nikons (and that 18-70).

From my observations, the 35/1.8 is almost always spot-on, with the camera not needing to do many corrections. The 16-85 and 85/1.8 are maybe a bit worse, but not by much. The only issue I have seen so far is that, in low light, when zooming the 70-200/4 in to 200mm and focusing very close, it sometimes keeps jumping around the focus point for a while, probably because the DOF is so thin. However, if I focus farther away and then retry, it locks on fine. The 17-55/2.8, which I just recently purchased, is a beast of a lens, but I put up with that because it's a joy to use, and that includes focusing.

I don't think the type of motor makes a difference whether or not a lens takes focusing corrections into account. A motor is just a device that converts electrical energy into mechanical energy, so I don't see how this can be (though, if anyone knows better, please let me know).

I will say this: in general, I have more confidence in Nikon's autofocus than in Pentax's.