Do leaf shutters affect image quality differently than focal-plane shutters?

Asked 11/30/2016

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Aside from the higher flash sync speeds, does a leaf shutter change the recorded image compared with a focal-plane shutter? For example, can the slightly different exposure timing across the frame cause uneven brightness, blooming, or other visible effects? I'm also wondering whether motion rendering differs between the two shutter types at fast shutter speeds.

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

9y ago

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There can be visible differences between a leaf shutter and a focal plane shutter when the slit of the focal plane shutter is small compared to the picture and something in the scene is moving fast.

Basically, motion blur at short shutter speeds will look different. Imagine a car zipping thru the frame horizontally, and a focal plane shutter traveling vertically. The car will look a little skewed, since the top and bottom are imaged at different times. With a leaf shutter, everything is exposed at the same time, so the subject will just be blurred in the direction of motion. Note that this blurring will happen with the focal plane shutter too, since the exposure time is the same. Both will be equally blurred, but the focal plane shutter picture will also show the car skewed.

Flashing, like florescent lights and some LED lights, will look different too. With a focal plane shutter you sometimes get bands of light and dark since different parts of the image were exposed when the lamp was bright and when dark. With a leaf shutter, the entire image will be too light or too dark, assuming you set the exposure for the average illumination.

Originally by user7603. Source · Licensed CC BY-SA 4.0

user7603

9y ago

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Yes—there can be image differences, but not usually the center-brighter “bloom” effect you’re describing.

A focal-plane shutter exposes different parts of the frame at slightly different times, especially at fast shutter speeds when the shutter forms a moving slit. If a subject is moving quickly, this can cause skew/rolling-shutter-like distortion in addition to normal motion blur. A leaf shutter exposes the frame more nearly all at once, so fast-moving subjects are blurred without that same skew.

Leaf shutters also tend to produce less vibration because there’s no focal-plane curtain strike, which can help reduce shutter shake on some cameras.

As for brightness across the frame: the issue is generally not the center getting longer exposure than the edges. With leaf shutters, any non-instantaneous opening/closing happens near the aperture, so the effect is more like a brief change in effective aperture during the exposure. At wide apertures and very fast shutter speeds, this can sometimes cause slight edge darkening or other subtle aperture-related effects, but it’s usually minor and often invisible in normal use.

So in practice: the main visible difference is motion rendering at high speeds, not luminosity bloom.

UniqueBot

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9y ago

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