Saturday, 29 August 2009

Dusty Postcards

BEFOREI just had to do a major sensor clean today and thought I would post some comments for those searching for information later.

Of course you don't HAVE to clean your sensor OR do it yourself. You can send it back to the manufacturer or drop it off to a repair shop. I did this when I bought my first D-SLR. I waited 2 months to get it back from Nikon and swore I would never do it again. Likewise, you can remove the "bad" spots from your pictures in post-processing using a clone tool, and I do this myself when I haven''t been able to clean in between shoot. Eventually you will have to clean your sensor.

Cleaning usually involves using a dry brush and a wet swab. How often you have to clean will depend upon the camera you have, how often you change lenses, and what environments you shoot in.

Disclaimer: I don't have great habits when it comes to keeping my sensor clean. I change lenses often and I often leave lenses off the body for a while. Sometimes I will remember to flip the body over so that the body opening is facing down in my bag and dust is less likely to get inside.

You will see sensor dust appear as black spots on your images. They are much more noticeable when you shoot at f22 than when you shoot at f2.8 (I won't bother to talk about the physics of why that is). You can check for dust by shooting a blank piece of white paper. Don't shoot in focus, as this will pick up any imperfections in the paper. So defocus, set your f-stop to 22 (or the highest value possible) and don't worry about shutter speed - all you are looking for is an out-of-focus white background to contrast the dust bunnies on your sensor.

You can usually see the dust form the display on your camera, but it is better to pull the image into your favourite piece of software and zoom in as you pan around the image.

Here is a shot from my cleaning session today:

BEFORE

Unfortunately, this is after several cleaning passes already and you can see there is still LOTS of dust on the sensor (black spots circled in yellow).

After a few more passes it cleaned up much better, although if you look close enough, you will still see some dust spots.

AFTER

You will notice I didn't bother to properly adjust the colour balance. In fact, this is a mixed light shot (light from a window and a desk lamp) I'm not looking for a great shot here, just something to highlight the sensor dust.

Many cameras allow you to load a dust reference shot. When you do this, the camera's built in software will attempt to remove the dust spots itself. This can save you effort in post-processing, although I'm always reluctant to leave this sort of judgement based task to automated routines. If you want to try it, check your manual for instructions on how to do this.

Depending upon your habits, you may have to clean more often or less often. When I shot with a Nikon D70s (no built in sensor cleaner), I usually cleaned my sensor once a month with a dry brush and once every three months with a wet swab. Sometimes more often if I shot in a dirty environment like a sandy beach. Now that I am shooting with a Nikon D700 (built in sensor cleaner set to clean on start-up and shut-down), I clean less often. Now I usually clean it every 6 months with a dry brush and once a year with a wet swab.

After a lot of research, I settled on Visible Dust gear. In particular Arctic Butterfly for my dry brush and Vswabs for my wet swabs. The pages linked above have really useful videos that will show you how to use these products. Note: The wet swab is a USE ONCE deal. Do not try to use it a second time (i.e., no second pass.) Make one pass and toss. If you need a second pass, break out a second swab.

Again, how often you clean depends on your habits and where you shoot. I just came back from shooting in Antelope Canyon where I was under tight timelines and the environment was extremely dusty. This meant I was changing lenses often and was pretty careless about how long my camera body was open to the dust. I certainly paid a price for this. My sensor was so dirty that I made 3 passes of the dry brush and three passes with a wet swab. That's 6 cleaning attempts following only one shoot.

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