you move too fast

sub-second shutter speeds

Toronto. Once dry plates were in common use, shutters became a necessity to make reproducible second and sub-second exposures. If “you move too fast“, you are blurry even though the shutter is set to ‘I’ for instantaneous. As years went by, light sensitive media and photographic lenses increased in speed, making truly fast shutters mandatory.

By mid last century, only two basic shutter designs were important: the leaf shutter and the focal-plane shutter. Leaf shutters allowed flash to operate correctly at any setting. Their downfall was the need to have one per lens since the most efficient location was between two groups of lens elements. Leaf shutters are both very complex, and limited by physics in their top speed. A few cameras placed the shutter right behind the lens so one shutter would work with all interchangeable lenses. The larger leaf size necessary to allow for fast aperture lenses, makes the shutter mechanism bulky and limited in its fastest speed.

Focal-plane shutters must be integral to the camera body. The curtain(s) move across the sensitive media at a rather slow speed. Since the first curtain has to be fully open and the second curtain not yet in motion for successful flash operation, flash synchronization is relatively slow (about 1/50th to 1/125th second tops).

In action, the first curtain is released across the focal plane followed at various times by the second curtain resulting in a variable slit. The slit width and spring mechanism determine the exposure. Old Graflex cameras used a single long curtain with various slits cut in it. Spring strength and slit choice were made following a table on the camera to create the desired shutter speed. Clumsy. Minicams that used a focal-plane shutter usually had two curtains and an automatic self capping function when winding the shutter and returning the curtains across the sensitive media.

Like the post on “Slow Down“, I used words from that Simon and Garfunkel song to title this post too. Of course in this digital age, and especially with digital cameras in smartphones, no one gives a hoot about shutter design any more.

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