In an earlier posting on scanner art, I lamented that scanners don't get enough love. Having used quite a few scanners over the years for purposes for which they were never intended, I have learned a few things in regards to their use as a creative vehicle.
1. Depth of field is the area in front of and behind the plane of focus that is reasonably sharp. You can assume that the plane of focus on a flatbed scanner is the surface of the glass. To be sure, this is not always the case and there are special systems of focus determination which involve shims and such to place film closer to the true plane of focus. I am more concerned with the understanding that as you move things further from the glass, the objects appear less sharp. This can be used to great effect. You can use this to provide a sense of depth in your image. If everything is equally sharp in an image, it tends to looks flat. Since the glass prevents us from utilizing the depth of field in front of the glass, we are limited to moving things further above it to make them less sharp. Of course, you can remove the glass if you would like to, put the design of most scanners is such that the scanning mechanism travels just beneath the glass preventing you from having images situated much below the glass surface.
One of the more interesting things pertaining to scanner depth of field is that it varies greater among various scanner models. It all has to do with the optical design of the scanner. For example, the Canon Lide series of scanners have incredibly shallow depth of field compared to say an Epson Perfection 3170 or a Perfection 4990. This isn't intrinsically bad, it is just to be noted. If you want to make a piece with very shallow depth of field, then get a Canon Lide scanner. If you want greater depth of field, get an Epson. This isn't to say they are all the same though. In the previous post on scanner art, I think I mentioned that everyone should have at least one scanner. Depth of field considerations is just one reason why.
2. Light fall off. Light scatters as it travels away from a light source. Opening or removing the scanner lid, less light will be reflected back onto the object being scanned. Usually, opening up the lit results in a black or very dark background as opposed to white. Depending on what you are going for, you can do either.
More to come soon...