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     Steve_s Tinkerer Username: Steve_s Post Number: 169 Registered: 07-2006 Rating: N/A |
About time I finished off this thread! I've had next to no time available the last 3 or 4 months for camera stuff, but have finally managed to find a few hours. With the tensions set for a roughly correct result at 1/1000 sec I checked the curtain speeds at 2 mm intervals across the frame at 1/1000 sec and at 1/50 sec. It was clear from this that at the slower speed the 1st curtain was accelerating more slowly up to the point where the 2nd curtain ran, then accelerating at the same rate as at 1/1000, but due to the slower start never getting close to the same speed as the 2nd; i.e. there is interaction between the curtains causing the stationary 2nd curtain to act as a brake on the 1st. There doesn't appear to be any significant contact between the curtains/ribbons/cords. The only other way I can see that the curtains can interact is at the main shutter spindle, where the 2nd curtain drum runs on the same spindle as the 1st curtain pulleys, and to a lesser extent where the 1st curtain runs over a roller on the 2nd curtain spring-spindle. I flush-cleaned both areas thoroughly and lubricated the main shutter spindle with a synthetic watch oil. There seems to be some improvement, though it's still very far from perfect. I'm running at curtain tensions of 2½ turns on the 1st curtain and 3½ turns on the 2nd, and results are now quite usable from 1/500 sec down. There is about .8 of a stop tapering at 1/1000, but bearing in mind that I've never used 1/1000 on any camera except as a test just to see if it works, I guess I'll have to live with that! For the record, I checked the curtain tensions on my Pentacon FM, which still had its blue lacquer on the lock-screws and had apparently never been touched. 1st curtain tension was 2.6 turns and 2nd curtain 3.1 turns. I let the tensions down very carefully and would guarantee the figures accurate to within plus or minus 1/10 of a turn. |