Sensor cleaning, part ouch

I wrote a post about camera sensor cleaning a few months back. It would seem that the concept of sensor cleaning is a little more complex than I originally thought. Maybe I was right to be paranoid.

Doug Pardee sent me an email with a warning about sensor cleaning, type of camera, and fluid used, and he gave me permission to re-produce:

Once upon a time, the front of the sensor assembly in every DSLR model was glass. You could just go in there and clean it with anything suitable for cleaning glass. The big concern was not making things worse by leaving spots and streaks.

In the past couple of years, however, some DSLR models have been designed with sensor assemblies that have exposed coatings on the front. Cameras that I know do this are the Canon EOS 5D and three cameras with dust-shakers on their sensors: the Sony Alpha DSLR-A100, the Canon EOS Digital Rebel XTi aka Kiss Digital X aka 400D, and the new Canon EOS 1D mark III.

This design change is basically a cost-saving measure, but the manufacturers seem to be spinning it as a “feature”. From what I can tell, the exposed coating in the cameras listed above is the dichroic “hot mirror” that keeps the sensor from being overly sensitive to infrared. The hot mirror coating is typically something like indium tin oxide, which is electrically conductive by nature. I believe that the manufacturers are spinning this exposed hot mirror coating as being an “anti-static” coating for dust control.

Ordinary Eclipse fluid has been known to attack hot mirror coatings. In the past, this only occurred when the sensor assembly was incorrectly assembled at the factory, accidentally resulting in exposed coatings. But now, sensors on some DSLR models are *designed* to have the hot mirror coating exposed.

Accidental removal of some of the hot mirror coating would cause the sensor to be overly sensitive to IR in those parts of the sensor where the coating was stripped away. In most photos that would not be noticeable. But some materials are particularly reflective of IR, notably clothing made of some synthetic fabrics. Some white paints also reflect a lot of IR. Photos of subjects with those materials can be subject to false color if the hot mirror is missing.

Photographic Solutions has developed a new cleaning fluid called Eclipse “E2” for sensors with exposed coatings. This was apparently done at the behest of Sony, who wanted a safe wet-cleaning fluid for the DSLR-A100. Sony has approved E2 for the A100.

Photographic Solutions recommends E2 for all four of the camera models mentioned above. But I was surprised to find four other camera models on that list: the Leica M8 and the Nikon D70, D70s, and D80.

Here’s the list.

I don’t know what coating(s), if any, are exposed on those four additional camera models. The Leica M8 sensor doesn’t even *have* a dichroic hot mirror coating – the photographer needs to use a separate hot mirror filter on the lens.

For an example of what the IR “false color” issue looks like, go to this article and scroll down about halfway. There are two photos there comparing a Canon 5D with a Leica M8. As I mentioned, the M8 doesn’t have a hot mirror coating on its sensor. Also note the other M8 photos that came out fine even without the hot mirror… er, well, now that you know what to look for, you might spot some less obvious false color in some of the other photos.

As I said, I don’t know what the situation is on the Nikon D70. But my recommendation would be to switch to E2 fluid. Photographic Solutions says that E2 is good on all sensors, with or without exposed coatings, so you could also use it on the D200. Or use your existing supply of Eclipse fluid on the D200.

Check ve-e-ry carefully about which sensor cleaning fluid you can safely use with your camera. Thanks muchly to Doug for heads up.

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