The Sensor

Putting up a nice safe technical post this week. What is the sensor and why do I care? If we just click the shutter button and expect to see magic happen on our screen, isn’t that enough? No, I obviously do not think it is enough or I wouldn’t be writing about it. The sensor is the heart of the technology of image capture. Without a great sensor none of this would be possible.

History

Going back, there was rubbing pigment on the wall of caves – Oops, too far. Photography as we would recognize it started in the early 1800’s. Motivated photographers had to mix their own chemicals and wet coat their own glass plates, in the field, in the dark, right before exposing them, then processing them quickly, in the dark, in the trailer they brought. Not for the short attention span crowd.

In the late 1800’s Kodak produced commercial coated transparent film, on a nitrate base. Keep it away from your candles – poof. A few years later cellulose based safety film was invented and replaced the dangerous nitrate film.

Around this same time roll film was also invented, so more than one exposure could be made before changing film. This was a contribution to most photographers. Leica’s adaptation of the 35mm film size and the development of an excellent, small hand held camera system greatly advanced the use of photography. In 1935 Kodak released one of the greatest advances in photography – Kodachrome film. Color photography was finally practical and it became very popular. A very large market for both color and black and white film developed with Kodak, Fuji, Agfa and many other brands vying for position.

This is not an exact history of the development of photography and all of its branches. The point is that the technology of recording images has always been central to photography and it has been a subject of heated discussion/argument by photographers. I have witnessed people almost coming to blows about Kodachrome vs Fuji Velvia.

Film Was Our Sensor

Most “serious” photographers had their 2 or 3 favorite films that they used regularly. They learned the characteristics of each well enough that they could predict the results. This is very important, because photography has always been a mixture of technology and art. How the sensor (film) records light is necessary to know so the artist can determine how to use it to achieve the results they want. Pushing the limits of the sensor technology was a common artistic effect.

But then photography’s “shot heard around the world” happened in 1975. From Kodak’s web site: “Kodak invented the world’s first digital camera. The prototype was the size of a toaster and captured black-and-white images at a resolution of 10,000 pixels (.01 megapixels).” From that trivial sounding start, Kodak killed it’s own business and the multi-billion film business around the world. Digital sensors forever changed the course of photography. And this was a good thing for photographers.

Digital Image Capture

Image capture in a digital sensor is completely different from film. Instead of photons of light causing a chemical reaction in the film, the photons caused the emission of electrons in the sensor chip. These electrons are accumulated over the duration of the exposure, then transferred out serially and sampled to “count” the electrons. From this, complex and high speed processing reconstructs an array of “pixels” (picture elements) which is so dense it fools our eye into seeing a smooth image. This constructed data set is recorded onto a memory chip in the camera. Then usually transferred to a computer.

Over the years, good engineering has improved the process so much that few people still argue that images from film are superior to digital captures. My personal transition happened in about 2004. I finally concluded that the Nikon D70 was at least at parity with 35mm film. That was a 6 Mega Pixel sensor. The image accompanying this post was shot with that camera. Now, when I look at a good quality scan of a 35mm slide compared to a capture off my 47 Mega Pixel Nikon Z-7 sensor I have to shake my head and marvel at the improvement of our photographic technology. Yes, some of this comes from greatly improved lens design, but the sensor is one of the biggest effects.

So with digital sensors I am free to push the limits more, to experiment more, to have more fun with photography, to post process to a much larger degree. Sensor development has removed many of the barriers of resolution, dynamic range, reliability, noise, etc. Photography now can be driven more by artistic vision than by a struggle to produce a usable image.

Do We Need To Understand the Technology Anymore?

Do we as artists need to know about the technology of our sensors? I believe YES. Photography is unique in being a strong mix of technology and art. A good craftsman cannot ignore either of them. These marvelous devices must be understood to be used to their full potential. Digital sensors have limitations and their own quirky characteristics. Dig in; understand the transfer curves; understand the dynamic range; understand the behavior at maximum brightness or darkness; understand noise; understand moire patterns. Understand other related things like the focus system in your camera. Nothing is trivial. But have a very high regard for the sensor.

Much more can be written about the sensor. I may in the future if requested. As an engineer I enjoy digging into the technology.

To the sensor developers at Kodak and Nikon and Canon and Sony and Fuji and all the others – Thank you!

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