Canon has announced its second camera based around a ‘single photon avalanche diode’ (SPAD) sensor. It’s a completely different sensor technology to the CMOS sensors we typically encounter, based on a completely different physical phenomenon, and able to measure the arrival of individual photons.

The MS510 is a box camera, designed for applications such as nighttime border surveillance and maritime monitoring over long distances. The MS510 has a 3.2MP Type 1 (∼131mm²) sensor, from which it derives 1920 x 1080 video footage, Canon says it has greater sensitivity to near-IR light than the previous model.

In conventional CMOS designs, a charge is accumulated as arriving photons of light trigger the release of electrons via the photoelectric effect. This charge builds up during the exposure and the magnitude of the accumulated charge is read out at the end of the exposure.

In a SPAD sensor, a powerful electrical field accelerates arriving photons so that the energy of their impact triggers an avalanche of electrons to be released within the semiconductor. This allows sensors to detect down to the sensitivity of individual photons.

Such sensors don’t need to accumulate charge before they’re read out, so individual photon arrivals can be detected as they arrive: continuously sampling, rather than capturing separate, discrete exposures.

And, because each avalanche of electrons is so distinct from any coincidental electronic noise, it’s possible to essentially factor-out all read noise from the system. However, the nature of light means that photon shot noise (the randomness of light) would still be unavoidably present in any photograph.

Nestling behind some magnifying optics is a Type 1 SPAD sensor, capturing 1920 x 1080 footage from its 3.2MP resolution. Image: Canon

These characteristics lend themselves very well to video capture in extreme low light. Canon has previously show its SPAD sensor visualizing a single pulse of laser light as it moves. The MS510 is geared towards slightly less rapid movement, and has a movable infrared filter, allowing it to capture some light just outside the visible spectrum, for even better performance in extreme low light.

Like its predecessor, the MS510 accepted broadcast lenses designed for Type 2/3 sensors, and features magnifying optics in front of the sensor to make full use of the sensor area.

However, while some of these properties sound like they would be useful for photography, and Canon has previously talked about the SPAD sensor matching the performance of a sensor 10 times its size, you shouldn’t expect to see a SPAD sensor in an EOS camera any time soon.

The electrical field required to accelerate photons as they arrive in the sensor uses much more power than the CMOS sensors we’re used to. We only have the figures for the MS510 camera as a whole, which includes powering its controllers and fan but, for reference, Canon’s other MS cameras with Super35 and full-frame CMOS sensors consume between 8 and 12W, whereas the MS510 consumes 24W. This suggests both battery life and thermal management would be challenging to produce a photographer’s camera. And, for now, at least, resolution.

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