Let’s start with a little theory. I propose that the same considerations taken into account in creating a perfect photograph also need taken into account when determining a scanner to convert film to digital negatives. To prove this, let’s start with a brief discussion on the photography.
A great photograph, aesthetics aside, is the result of the proper film being exposed to light through a high quality glass lens for a proper amount of time. Light, glass, film – all three make the perfect photo.
Light is always perfect. There can be varying amounts of light and the light might not be covering the subject in the desired manner. However, the light is there nonetheless and correct measurements must be made of the light to provide a proper exposure.
This light then hits the emulsion of some film and records the patterns creating a negative (or positive in the case of reversal film). Different films have different sensitivities to the light. This means some film records more detail (high speed film) in a given amount of light and some less detail (low speed film). Knowing what size the ultimate photograph will be printed in along side the subjec matter an anticipated available light, determine which film to use.
For small 4×6 prints, just about any speed film will provide a good print. For a 13×19 print or 24×48 print, a slower speed film is typically used. The slower the film, the more light needed to expose the image, but the less grain is also present.
Lenses and Glass
Leica engineers have long studied and perfected the art of removing abberations caused by light moving through glass. Erwin Puts has written volumes about lenses including a 2002 Compendium on Leica Lenses their Souls and their Secrets.
Light bends through glass and comes out the other side. In the course of bending various abberations show up: flares, comas, loss of contrast and other problems that impede the recording of an image on the film. Different physical types of glass in different configurations help adjust the bending of the light to come out the other side and expose the film where we want it to.
This means the best glass in the best configuration has the best chance of producing the perfect photograph.
Light through glass onto film produces the photograph. To take a negative or slide and create a digital image, we pass light through the film through glass in a scanner to an electronic CCD to record the result. Thus, Light, glass and film qualities must be taken into account a second time to take the perfect photograph and convert it to the perfect digital image.
See Part II of Scanning Negatives – Hardware Considerations for the discussion on scanner hardware that this applies to.