Archived posting to the Leica Users Group, 1997/07/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Paul Schliesser wrote: >One of the big mechanical difficulites is that both curtains need to >travel at exactly the same speed, so that as the second curtain follows >the first, the distance between them stays the same. They also need to >instantly accelerate and instantly stop, without bouncing. The top flash >sinc speed gives you an indication of how fast the curtains move--if the >sinc speed is 1/250 of a second, it will take slightly less than half of >that time for each curtain to move across the frame. I think that with a bit of further deliberation you will see that if the sync speed is 1/250 of a second, and say, the electronic flash is expected to do its stuff in 1/1000 sec, then a shutter curtain could take 1/250 - 1/1000 sec to cross the film gate. That comes to 1/333 of a second, which is a lot longer than 1/500 sec. Anything faster is a bonus. On the other hand, the mirror has to stay out of the way for 1/333 + 1/1000 + 1/333 sec, or 7/1000 or 1/143 of a second, plus it has to fly up and afterwards flop down and settle quietly, which all takes a lot longer. If the mirror can cycle in 1/25 sec, it's doing a very, very good job, adequate for an 8fps motor drive. The Nikon F5 probably has this sort of cycling speed. Faster fps has required the pellicle mirror, both by Nikon and Canon. Or you can use the alternate firing method, which I believe Leica R8's are (will be, when the motors arrive) capable of - if you have duplicate focal lengths, and are not too close to the subject. * Henning J. Wulff /|\ Wulff Photography & Design /###\ henningw@archiphoto.com |[ ]| http://www.archiphoto.com