CREATING THE DUST-OFF REFERENCE PHOTO

Once you have the camera ready, hold the lens about 4 inches (10 cm) away from the subject. The camera will not try to autofocus during the process, which is good, since you want the lens at infinity anyway. We are not trying to take a viewable picture, just create an image that shows where the dust is on the sensor. Focus is not important, and neither is minor camera shake.

 

If you try to take the picture and the subject is not bright enough, or too bright, you will see the following screen (Figure 2).
If you don’t see the screen in figure two, you have successfully created a dust off reference photo. You will find the following image on your camera monitor. (Figure 3)

A two-megabyte file is created on your camera’s image card with an ending of .NDF instead of the normal .NEF, .TIF, or .JPG. This NDF file is basically a small database of the millions of clean pixels in your imaging sensor. (Example filename: DSC_1234.NDF) You cannot display it on your computer. It will not open in Nikon Capture or any other graphics program that I tried.

Now, copy the .NDF file from your camera’s memory card to its own folder on your computer’s hard drive, so that you can use it the next time you want to remove new dust spots from your sky pictures. Keep this folder for dust reference images, and give it a name that will help you remember what the files are later. I called my folder DustOffRef.

Now we’re ready to move into Nikon Capture and use our new reference photo on some images.

At the end of this article you will find information about this reference file for early Nikon DSLRs. (See footnote*)