Recently, i was shopping around for a used DSLR. But i don't have the experience or knowledge to check for sensor contaminants. I wouldn't want to end up with a DSLR with dirty or worst, a damaged sensor.
After consulting with my fellow seasoned DSLR user friends and the friendly google search engine, i managed to gather enough knowledge on checking DSLR sensor.
I was glad i did some study on this as it has help me identify some "bad" DSLR during my "shopping trips" and avoided costly cleaning or repair cost.
Since there is quite a large number of people buying used DSLR cameras, i thought maybe this might be useful to you guys.
Here's the simple test you can do anywhere to check for dirt and dust on the DSLR sensor :
Materials required : Plain Blank White piece of paper (A4), Appropriate camera lens (Try to standby 2 lenses if you can, if not, 1 lens will do. The second lens is to verify the results of the first lens if "suspected" dust is identified).
1) Fix up the lens to the camera to be tested.
2) Switch lens mode to manual. Set focus to infinity.
3) Set the aperture to its smallest value (largest number), at least f22, f32 if you have it.
4) Take a shot of the white piece of paper. Try to fill the frame with the paper sheet so that all you get is a blank, white image. Make sure the shot is "bright" enough.
5) Select "Playback" from the camera(or download the picture to a computer) and zoom(a least 4 -5x) into the picture. Scroll around the picture and look for black dots/hair lines or things that are black. I have come across contaminates on sensors that look like tyre skid marks. I suspect the damaged might be induced during DIY sensor cleaning.
Hope this tiny little info will be helpful to you guys shopping for a used DSLR.