The Slow Mo Guys’ Gav updated an earlier video where he filmed shutters travelling at a very high frame rate. The update adds a film camera to the mix as well as an extended comparison of focal-plane shutters to leaf shutters (an article on Analog.Cafe explains them too: analog.cafe/r/focal-plane-…).
The biggest advantage of a digital shutter over a film camera’s mechanical shutter is speed. But that applies to a focal-plane shutter, which can only fire at a certain speed to synchronize with flash — any faster and the exposure becomes uneven.
Leaf shutters are immune to uneven flash exposures at higher speeds, as they behave like apertures that expose the entire plane. For example, closing down an aperture to f/16 does not create vignetting or a black circle around an image (for an explanation of this counterintuitive property, see this article: analog.cafe/r/what-is-aper…). And because of that, leaf shutters can properly expose with flash at any speed selection.
The video goes beyond those distinctions, explaining how digital cameras’ electronic shutters cope with uneven exposure issues of their own. Gav could not film electrons moving through the sensor; instead, he showed an animated diagram, which felt a little confusing and did not explain how a global shutter can achieve an instantaneous readout or why it’s a standard on CCD sensors and uncommon in modern CMOS designs.
Rewatching the diagram helped. As for the questions I had remaining, I found the answers elsewhere:
- Global shutters work thanks to the Transfer Gate mechanism, which works like a shutter, but each pixel has its own. That way, all pixels can be turned on or off simultaneously. Transfer Gate does not block light; instead, it shuts the flow of electrons.
- CCD sensors have fewer interfering components at each pixel compared to CMOS, which leaves ample space for individual Transfer Gates. To counter this, new CMOS designs burrow some components deeper beneath the surface.
This research paper includes a very technical explanation and a cool electron microscope image of a global-shutter pixel: researchgate.net/publicati….
This article posted on the Samsung Semiconductor website explains their global shutter technology in less technical terms: semiconductor.samsung.com/….
This article explains the difference between CMOS and CCD sensors: gatan.com/ccd-vs-cmos in fairly simple terms.
“Introduction to CMOS Image Sensors” is a detailed, moderately technical explanation of the CMOS sensor technology: evidentscientific.com/en/m….
Dmitri