screwdrive

I keep on reading in the posts, Articles with reference to screw drive option with lenses. Please can someone explain to a complete novice. What infact screwdrive actually is ?

Cheers

Stuart

It's the method Pentax first used for auto focus. The focus motor is in the camera body and the screw drive transfers the motion into the lens to move the glass elements that actually focus the image. It's the little round peg bottom right as you look at the front of the camera mount. Now they seem to be moving to SDM auto focus where the Sonic Drive Motor (or something like) is built into the lens.

Generally referring to the mechanical drive from camera to lens, that operates the autofocus mechanism in the lens. The newer Pentax lenses have just the 'SDM' drive, while some have both.

Older digital camers will generally support screw drives, while some (the K10D for eg) got access to SDM via a firmware update. I say 'generally' because the K10 apparently lost the screw drive capability if an SDM lens was attached, after the installation of that firmware version. That's a problem if the SDM drive mechanism in the lens fails - and that's happened once or twice before.

Thanks Barrie..That clears that up... No concern to me as im a K-X owner,,

Cheers for the prompt reply..

I think your K-x will still have the screw drive so that it is compatible with the older lenses.

Screw drive is still available in the K-5. I believe in order to maintain their famous backward compatibility it will still be available in new Pentax bodies.

The new lenses however, with the exception of the limiteds, will be either SDM or DC instead of screw drive.

Now you've been and gone and dun it Gwyn



What's DC ?

DC is the af system in, for instance, the new 18-135. Not sure how it works - no doubt Stefan can blind us with science - but it is nearly silent, like SDM lenses.

I have no idea whether DC lenses work on a K-x though.

It's quite probable that any Pentax body equipped with the electrical contacts required for SDM lenses will accept DC lenses.

Let's hope so!

You are right and it does use the PZ contacts like the SDM AF.
the DC seems to stand for Direct Current so it's most likely a Different motor than SDM.

DC will be used in DA lenses and SDM in DA* according to an interview.

Acccording to link it means Direct Current for the AF motor. I could be proved wrong, very wrong, but I would have thought it should work on any camera with SDM.

They will according to Barrie's link.

As a cynic, it appears that Pentax foray into the "motor in lens" was named SDM. It has received a bad name for its apparent perception of failure. The other lens manufactures use a whole host of names (USM, HSM...) to refer to the "motor in lens". Essentially they are all variations on a theme. All of them are essentially motors with electronics to permit accurate, quick operation.

So as SDM is now perceived as "bad", Pentax had to think of a new name. Hence DC. I do not believe it is fundamentally different. If a Pentax camera can drive a SDM lens, it can drive a DC lens (or even a Sigma HSM lens)

Tim

This was confirmed by someone recently, I think it was the Ned Bunnell interview. All Pentax bodies that are compatible with SDM (including the ones that needed firmware upgrades) will be compatible with DC.