Leaf shutter vs focal plane sync speed

I hope this will not seem too ignorant a question, but I would really appreciate it if someone could explain to me why a lens with a leaf shutter

can have a much higher sync speed for flash than the more typical focal plane shutter in a camera body? Shutter speed is shutter speed,

right? So if a speed of say 1/500 is too fast for full flash coverage with a shutter mounted in the body, why is it not too fast just because the

shutter is mounted in the lens? Thanks for any answers.

 

Steve

A focal plane shutter consists of a front (leading) and rear (trailing) curtain (or blade) which traverse the film gate near the film plane at a constant velocity. The maximum sync speed is the highest speed at which the entire film gate is open at one time. At higher speeds, the distance between the front and rear shutter is reduced so that any one point on the film receives the correct exposure but the entire film frame is not exposed at the same time. If you use an electronic flash at a shutter speed higher than that amount (you can fool the camera using a PC port), part of the film will be blocked, leading to a partial exposure.

 

A leaf shutter opens from the center outward then closes. The entire aperture is open completely at the mid point of the exposure, regardless of the shutter speed. Since the shutter is usually located close to the optical center of the lens, all parts of the film plane receive the same exposure (i.e., there is no significant vignetting).

I think the answer may also be that the leaf shutter is somewhat smaller than the focal plane shutter (at least I think it is). The large film/sensor area in MF cameras necessitate large focal plane shutters where the blades have to travel relatively far with relatively massive moving parts when compared to, say a 35mm or APS-C shutter.

Thanks fellows, that helps explain it to me. I know, but just did not think about, the first and second curtain on the focal

plane shutter, but I was still not real clear on the leaf shutter. Thanks again for the answers.

 

Steve

Andrew,

 

You lose one turn :-) Go back to basics, do not pass go, do not collect $200.