| Author | Message | ||
     Alex Rating: N/A |
Quite a few M42 lenses, when mounted on my Yashica TL-Electro, show an odd phenomenon. Pressing the shutter release stops down the lens, then it sticks, the shutter doesn't fire, and the mirror stays in the up position. Easing the lens to unscrew then lets the shutter fire and the iris opens back up. What seems to be happening is that on some lenses, when the kicker plate strikes the diaphragm stop-down pin, there's enough resistance to stop the kicker plate in its tracks. When I simulate this with the lens off, using my fingernail to inhibit the kicker plate, I get the same phenomenon - mirror lifts, but shutter won't trip till I let go. So I reckoned that perhaps the stop-down pin was a fraction of a millimetre too long, catching the kicker plate early in its travel, and offering enough resistance to stop it. When I first noticed this, on a fairly cheap Hoya lens, I gently filed down a little off the end of the stop-down pin, until the iris stopped down correctly and didn't need the lens unscrewing to let it open again. Of the six M42 lenses I have tried (two Yashicas, four CZ Jenas), four have exhibited this phenomenon (one Yashica, three CZJ), and in each case, filing down the stop-down pin has cured it. However, I can't help thinking that there might be some adjustment that could be made to the kicker plate instead, but I don't know how I'd set about that. But I'd rather try that avenue that have to take a grinding tool to the pin each time I buy a new screw-fit lens. I'd be grateful, as always, for any pointers or suggestions. Alex |