Monday, July 11, 2011

Disassemble the DA21 Limited (and the Secret of the QSF Mechanism)

A Chinese Pentaxian (who is actually a camera/lens hacker!) has DIY to repair his DA21 with shifted infinity collimation position (over time) so that his could not focus at infinity as the far end of the focusing ring always hit the boundary:-
(Simplified Chinese, Google-translated English Page Here)

He disassembled both the rear and front parts of his lens in order to find out what he could do. Here are two of the posted pictures:-

On the course of disassembling the rear part, he discovered the secret of the Quick Shift Focus (QSF) mechanism. Below is the key components of the driving gears:-

He tells that the gears are designed in such a way that the driving force is only transmitted in one direction. That is, when the lens is driven from the AF motor of the body, the focusing ring will turn. On the other hand, when the focusing ring is turned by hand, the gears will be de-linked automatically, and that's how the QSF works.

Whilst I think he is mostly right. But however, I think the QSF is just more than a pure mechanical thing. As none of my DA lenses works with my older Pentax film SLR bodies like the MZ ones. The movement sometimes is limited in one direction and sometimes is not. As such, I suspect there is also some kind of electromagnetic mechanism to make it fully works.

Later on, the hacker discovered that it was not about the rear part for the problem he wanted to tackle and it should be about the front part. So, after some more inspections and trials, he finally found the key components that he should re-adjust and then re-applied the lubricant, here they are:-

So, he finally succeeded for what he had done in the whole course. Congrats, guy! But sometimes I just wonder, why so many Pentaxians needed to DIY but not sending their gear to the local Pentax service centres for calibration, adjustment and repairing? Is that the Pentax service quality could never meet the users' demands and the charges are too expensive and the places/opening times of the centres are rather inconvenient? ;-D

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