PhotoModeler makes an assumption that the imaging media is a perfectly flat plane. This is very close to being true with small CCD chips found in video cameras and in some of the digital cameras. This is not usually true in a film camera. Large-format cameras (such as an 8x10 film camera) can have a lot of problems with film flatness. Careful photographers will use vacuum platens that hold the large pieces of film flat during exposure. In a good 35mm camera, the film will be relatively flat but might still bow a bit. Typically, CCDs have better flatness characteristics than film.
All imaging devices have limits of resolution. The light ray coming from some feature on the object and intersecting the imaging media will be blurred. It will be blurred by both the lens and by the media itself. In a CCD, this is due to a finite size of the image sensors and in film this is due to a finite grain size. The higher the resolving power of the imaging system (lens and media), the more precisely we will be able to identity where that light ray hits the media. The more precisely we can identify the location of the light ray, the more accurate our measurements will be.
Therefore, a high resolution CCD is better than a low resolution CCD and fine-grain low-speed film is better than coarse-grain high-speed film. Today many CCDs have similar resolving power to film and this will continue to improve.
When using film, you must take into consideration how the film is digitized for computer use. There are four different scanning technologies available to the consumer today:
• Flat bed scanner,
• Hand held scanner, and
• Slide scanner.
All of these scanners involve mechanically scanning a sensor or mechanically shifting the film. All scanners add further distortion to the image captured on film. Making mechanical movements precise can be expensive and so many consumer-grade scanners are not very precise.
The other three scanner types can scan between 100 and 3000 dots per inch. A good office flat-bed scanner can capture up to 600 dots per inch. If you scan the 35mm film negative directly you can get up to 850 by 560 pixels. This is comparable to a good broadcast quality video camera. If you print and blow-up the negative and then scan it, you can get very high resolutions (up to 5000 by 3000 pixels on an office flat-bed) but you would have introduced another distorting step (printing the negative on photographic paper). We suggest that a flat bed scanner not be used with enlarged prints with PhotoModeler; the accuracy and distortions effects are too unpredictable.