When you want to scan 35 mm slides with a flatbed scanner, you'll see that these scanners are made for images that are flat on the glass. Mounted slides look out of focus. But you can fix this by removing the slide from the mount and placing it directly on the glass. The slides also turn out to be much too dark in the scan. To avoid this, you could build a simple backlight out of paper to reflect light from the scanner. Or you can use the brightness of the iPod screen to obtain pretty good results.
If You Have No Time For That, Use Lafayette Slide Scanning
If You Have No Time For That, Use Lafayette Slide Scanning
Source: http://industrialarithmetic.blogspot.com/2010/01/how-to-scan-35mm-slides-using-flat-bed.html