How To Create A Test Image
To Check For Dust
To make a test image, you can use about any lens you want but, a non-wide angle lens works better then a wide angle just because of the normal falloff found in most wide angle lenses. You want as much of an even exposure as possible from corner to center. The second consideration is minimum aperture opening; we suggest a lens that will stop down to f/22 or greater. We have found that a great subject to shoot for the test, is your monitor. Seeing that you already have to use a computer to view your test, there is no need to go elsewhere to make the test. You already have a willing and qualified subject right in front of you, why not use it. Prepare your monitor for shooting the test:
- Create a new image in Photoshop
- Fill it with white (most any solid color will do, but we prefer a lighter one)
- Set the camera to the following:
- Mode - Aperture Priority
- Setting - Aperture to minimum f/22-f/45
- Lens - Manual Focus set to closest focus setting (if shooting the blue sky, then infinity)
- Features - Turn "OFF" all special function like "sharpening"
- Zoom in until it fills your screen
- Take Picture - shoot camera facing your monitor. Depending how bright your monitor is, your exposure may be a couple seconds. During this exposure, move your camera back and fourth being careful to not to point the lens outside of your white box. Moving the camera during the exposure insures that you are not taking a picture of dirt on your monitor. This should be done within a matter of an inch or two from your monitor.
- Photoshop - Take the image into Photoshop and do a "<CTRL><SHIFT>L" for "auto level" You can lighten or darken if needed.
- Inspect Image - You can now see where you do or do not have dust. Remember that what you are looking at is an image that is flipped 180° vertically (top to bottom) from when you're looking straight in on your sensor. What shows on the bottom of the image will be towards the top of the camera and visa versa...
Before Converting in Photoshop
Converting in Photoshop
After Photoshop and Before Cleaning