Originally posted by Pheo
I fed exactly this point back to the Pentax rep - he asked me what I was missing - A replacement for my Tamron f2.8 17-50mm with WR - "what about the 16-50mm DA*" - Informed him I wouldn't touch it due to its bad rep with SDM motor failures, and that SDM not being fast enough. We talked for some time about the possibility of adding the DC motor to more lenses, he seemed as perplexed as me as to why this couldn't be done.
If the in-body motor is fast and silent, why even bother to continue in-lens focus motors of any kind?
It is clear to me that screw-drive lenses are extremely reliable versus in-lens motor designs (of any brand, and yes, there have been issues with in-lens focus motors of other brands), and you pay for only one focus motor versus one with every lens. Pentax has a quick-shift design that works just fine with the screw drive as well.
The screw-drive lenses I have are faster than any SDM lens I have owned, and while they might not keep up with a ring-motor design, they have to be far cheaper to make.
Putting a motor in the lens also means that the lens will never perform any differently than the day it was designed. While you are stuck with the gear ratio chosen for a screw-drive design, with the motor in the body, you can improve it with every generation and all lenses will benefit.
You have to have an in-body motor anyway to keep the backwards compatibility that Pentax is known for, and the main knock I hear against screw-drive lenses is the noise (which I am sure is mainly the motor in the body), so a fast and silent in-body motor is a simple and brilliant solution.
I hope that Pentax continues to think out of the box and doesn't listen to the folks that want the brand to "me too" everything CaNikon does, as that will leave only one way to compete: price.
I was holding out for the discounted K5II, but I may have to scrape up enough for the K3 if the IQ looks good.
Ray