What is the principle focus Pentax screwdriver and ultrasonic motor focus what is different?
Summary: the drive mode, because the belt drive system the cost a little higher, and the use of a low cost lens; there is no body drive system, the cost will certainly be lower, the cost is passed on to it to every one of the normal use of the lens, the lens must be because of the use of built-in driver function. Pentax has no reason to give up the drive system, the first is the driving way is quite reliable, save a lot of cost (Pentax lens, have a lot of double drive mode of the lens, such as several star head and so on, ultrasonic motor, more out of the lens a lot more expensive, we all know); also the Pentax is recognized in the game player kind, his new machine PK for all previous film era production export support the use of automatic lens. It also includes all the 42 bolts of the Montague, as well as the huge manual lenses of the K, M, and A series. Really make the most of it, it is to save a lot of money for the game player in turn itself Pentax Pentax, less sold how many new lenses, earn much money, simply not statistics.
The disadvantage is a little noise, focusing speed is slightly slower. And then the rising lens built-in ultrasonic motor, the advantage is focus action faster, less noise, and its durability to be observed (once the mirror motor damage, replacement cost is not expensive).
The so-called "screwdriver focus" was used by almost all brands of automatic film SLR in the early years, and the focus of the lens was driven by the body motor. Then use the Pentax (Nikon) Sigma, Samsung and so on Digital SLR, the utility model has the advantages of good durability, low failure rate, the corresponding lens has low cost.
