Shutters

I wrote this article primarily to be sure I understand all the stuff I am writing about. It is therefore fairly basic, and you might get bored in reading it. I do however hope to get some things straight for people who, like me, have difficulties understanding the basic facts of photography. That's why I put it on my web site. If you find that insulting, or appreciate it but want to correct me in one point or the other, please contact me.

Talking about today's cameras, there are basically two types of shutters:

• leaf shutters
• focal plane shutters

Leaf shutters are situated within or immediately behind the lens, are typically made of metal and found on:

• view camera lenses
• twin-lens reflex cameras
• some medium format camera lenses (e.g. the Hasselblad 500 series)
• most cameras with fixed lens (e.g. the 1970s compact rangefinder cameras I love so much)
• some (very few) interchangeable lens 35 mm cameras like the Kodak Retina IIC and Retina Reflex, Braun Paxette, and Altix

Focal plane shutters are situated next to -er- the focal plane - i.e. just in front of the film. They are made of cloth, rubber or metal, travelling horizontally or vertically and found on most 35 mm cameras with interchangeable lenses like SLRs and RF cameras, the most prominent example for the latter being the Leica (both screw mount and M series). They are also found on medium format rangefinder and SLR cameras.

As you know or might have guessed, both have their advantages and disadvantages:

• focal plane shutters are made out of two shutter curtains. Shutter speed is determined by the distance of the shutter curtains, which typically travel at a constant speed. Consequently, at faster speeds they expose one "strip" of the film after the other by way of an open "slit" between the shutter curtains travelling along the film. Shutter speeds up to 1/8000 and shorter are feasible.
• The fact that the focal plane shutter does not expose the whole of the frame at the same time has two downsides:
  • flash sync time is limited to the shortest time at which the frame is exposed as a whole at a time, this is typically not too fast (1/50 on Leica M, up to 1/250 on SLRs)
  • with fast speeds, objects moving in a direction perpendicular to the opical axis are compressed or extended, depending on the direction they move in relation to the direction the shutter travels.
• focal plane shutters leave plenty of room in the camera for metering off the shutter curtain or the film itself, and for adapting interchangeable lenses.
• leaf shutters, on the other hand, do restrict lens design if the lenses are interchangeable. Either the shutter is within the lens, which makes only the front elements interchangeable and compromises lens design a lot (that's the way the Kodak Retina RF and SLR cameras were constructed) or it is behind the lens, which -- also compromises lens design a lot, at least as far as wide angles are concerned.
• leaf shutters offer a limited range of speeds (typically up to 1/500, as the shutter blades have to travel the whole clear aperture of the lens (which can be a long way in the case of a fast lens). I seem to remember Minolta offered a leaf shutter camera with a top speed of 1/2000 one time, but the top speed was only available at apertures of f/8 and smaller. On the other hand, the Konica Hexar AF offered a top speed of 1/250 (as do many MF lenses) which was widely criticised but explainable, regarding the clear aperture the blades have to cross. On a lot of cameras, the top speed of 1/500 is hardly reached with the lens wide open.
• on the other hand, leaf shutters allow flash sync at all speeds, as the whole frame is exposed at one time, whatever the speed may be.
• leaf shutters tend to be much quieter and produce less vibration, as their movement is centered rather than directed. As a consequence, many photogs feel they can hand-hold slower speeds with a leaf shutter. The obtainable speed depends on your hands and on the weight of the camera, but 1/15 to 1/4 seem realistic with moderate wide-angle lenses. On SLR cameras the shake caused by the mirror flipping up makes this a theoretical consideration, but most SLRs are equipped with focal-plane shutters anyway.