By Richard Sherman
I recently posted a link to Canon’s announcement about its 3.2 megapixel SPAD sensor on the Discord server, but I didn’t see any comments. This is a potentially revolutionary announcement for astrophotographers so I thought I better share a bit more in Sidereal Times.
As a professional photographer, I receive a lot of product release news, but this one stopped me in my tracks. On December 15, 2021, Canon announced that it had developed a 3.2 megapixel SPAD sensor offering “higher resolution than full HD images even in low-light environments.” A SPAD sensor, or Single Photon Avalanche Diode, is an alternative to the CCD and CMOS sensors that are familiar to astrophotographers. Perhaps the key in that jumble of acronyms is “Avalanche.” With SPAD sensors, just one photon of light is needed to reach each pixel in order for a usable image to be created. If you think about digital camera sensors as having a bunch of little buckets across the sensor plane waiting for light to pour in, then a SPAD sensor only needs one photon per bucket. The sensor then creates an “avalanche” of electrons based on just one photon. In contrast, CMOS sensors must wait for more photons to fill up the buckets to create a usable electrical signal, resulting in longer exposure times and electronic noise. And noise is the enemy of astrophotographers.
SPAD sensors have been around for several years, and firms like Sony and Panasonic offer versions of it. You can read more about the technology online (e.g., 24,000 frames per second, and three dimensional imaging), but I will wrap up with a quick list of potential astrophotography benefits with the new 3.2 megapixel version from Canon.
- Clearer images in low to “no light” environments. Please take a look at the far right image above. That image is taken in light imperceptible to the human eye!
- Faster images. Because SPAD sensors only need one photon, the “shutter” (which is no longer mechanical but a virtual one that opens or closes the buckets of pixels in mirrorless and astronomy cameras) needs to be open for a fraction of the time that a CMOS sensor requires. Canon claims its new sensor needs only one-tenth the amount of light as CMOS sensors, and I suspect it could become even more efficient over time.
- Potentially darker skies. These sensors have immediate applicability in security cameras. So instead of lighting every corner of a warehouse at night, we can turn off the lights and still “see” clearly faces and license plates in color in the dark.
Canon plans to begin manufacturing the new 3.2 megapixel SPAD sensor in the second half of this year, and a new manufacturing plant in Japan will be built to scale production. How long we have to wait until this sensor reaches our astrophotography cameras is uncertain. Once it does, however, we will be enjoying low noise images of deep sky objects that might be imperceptible in our existing CMOS or CCD cameras. And for those who enjoy taking photographs of the night sky and the Milky Way without a telescope, we will be able to throw away those heavy, annoying tripods.
I hope this article is helpful, and that everyone is as excited is I am for the next-generation of astronomy cameras based on SPAD sensors. As Hall of Fame musician Tom Petty sang, “the waiting is the hardest part.”