How to Solve the Sensor Dust Problem Once and for All
Posted on 15. Oct, 2009 by Thomas in Blog, Photography
If there’s one downside to being a Digital SLR owner it’s the problem of sensor dust. While it doesn’t affect everyone, depending on the type of photography you shoot, it can be a real pain. If you’re a landscape photographer in particular and you tend to shoot with the lens stopped down you’ve no doubt run into this issue time and again. For the most part it’s a case of cloning out the uninvited guests in Photoshop and periodically cleaning your sensor. Since companies have started adding video to their cameras, the problem has become more of an issue. While you can easily clone out a few spots on a still, it’s extremely difficult to do it on moving footage. Wile recently camera manufacturers have started adding anti dust technology to their cameras, which usually consists of some kind of mechanism to vibrate the low pass filter in front of the sensor shaking the dust off, the problem is they don’t work very well. Sensor dust is one of those things that most photographers learn to live with and work around, but the funny thing is, Canon actually had a solution to this problem, one which would eliminate sensor dust completely, and they had it way back in 1965 before anyone had even dreamt a digital camera.
In 1965 Canon introduced an SLR called the Canon Pellix. It was Canon’s first cameras to use TTL metering and did so by placing the metering sensor behind a fixed semi transparent mirror called a pellicle mirror. The meter cell would swing out from behind the mirror and the lens would be stopped down for exposure dimming the viewfinder, but unlike standard SLRs the viewfinder would not be blacked out. Canon continued to evolve this technology periodically using the fixed mirror design to create cameras with a high frame rate, culminating in a version of in their flagship SLR, the EOS-1. In 1995 Canon came out with a special version of the EOS 1 called the EOS 1 RS. The idea behind this was to make a high speed version of the 1D. The ID RS could shoot a whopping 10fps. Bear in mind this was using 35mm film and not a digital sensor. This was quite a feat for its day. One of the tricks this camera used to pull off its high frame rate was the use of the fixed pellicle mirror. Like with the early Pellix, and unlike a traditional SLR where the mirror swings up to allow light to get to the film or sensor, the pellicle mirror never moved. Because it was semi transparent half the light went to the viewfinder and half went to the film when the shutter was opened. This allowed Canon to do away with the mirror lift mechanism therefore considerably speeding up the process of taking a picture.
The thing is, this technology could get rid of sensor dust once and for all. If a DSLR was fitted with a fixed pellicle mirror like the old EOS 1-RS the whole mirror box and sensor chamber could be completely sealed. While the pellicle mirror design was abandoned because of, ironically its susceptibility to dust and dirt, unlike dust on the low pass filter however it would be out of focus. It would also be considerably easier to clean. The only issue would be the light drop off compared to a standard mirror mechanism, but with today’s sensors this wouldn’t really be that much of an issue. Anyway, it’s just a thought. I’m sure there are technical issues preventing this from working or surely someone would have tried this before now, but it’s one to think about.
Related posts:
It’s an issue for the photographer in real time as well. The image in the viewfinder will be darker.
Yeah, that is true, but I would hope that improvements in technology since 1995 could at least minimise that problem. It’s just an idea anyway.
I’ve been reading a few posts and really and enjoy your writing. I’m just starting up my own blog about my new Canon 500d and only hope that I can write as well and give the reader so much insight.