The Photography Tip of the Week #068

Posted by Philip in Photo Philosophy, Podcast

Sensor Check

068 Photography Tip of the Week (audio)

When you have a nice warm summer day and the sun is high in the sky, it’s a perfect time to check your sensor for dirt and dust. This isn’t like having to deal with airport security. You aren’t going to get raked over the coals if your sensor is dirty. But it is valuable information and will help you have the sharpest images possible. So here’s what you do. Get a white sheet of paper and take it outside and put it on the ground in direct sunlight. This will be the whitest this sheet of paper will ever get. White balance isn’t all that important, but aperture is so put your camera on aperture priority and set it to f/22. Set your ISO to 100 so you’ll have the least amount of noise and focus on the corner of the paper. With the focus locked, fill the frame with the bright sheet of paper and take the shot.

That’s a wonderful masterpiece you have there now. In some cases if you have really nasty spots you’ll see them immediately. But in most cases you’ll have to load the image in an image manipulation program and play with the levels. What we’re looking at here is a sensor I haven’t cleaned on one of my older camera bodies. You can see from the level histogram that it is displaying mostly white which is good. If it isn’t like this, you may have a serious problem with your sensor.

When you change the levels by moving the black level toward the white, you may see spots and debris on the image. Some of this may be on the lens. You can use multiple lenses at the same settings to compare and determine if the spots are on the lens or on the sensor. If you only have one lens, clean the lens between shots and compare those images. Any difference will most likely be sensor dust.

Now let me show you what a clean lens and sensor looks like. The regular white shot is as you would expect. Mostly white and a true masterpiece if you like photographing polar bears in a blizzard.

When you move the black point here, you will start picking up the inherit noise of the sensor and the grain of the paper. No spots and splotches here. If you do feel that you need to clean your sensor, do this test first to determine if you really need to. If you do, clean the sensor and do the test again to see the difference. I wouldn’t suggest using glass cleaner or anything other than a professional sensor cleaning fluid and brushes. Even though you are actually cleaning a piece of glass protecting the sensor, non-specific cleaning products can leave the sensor with more streaks, spots and dust than what it started with.