EPM Tech Tip 066: Density, Contrast and the 1.00 Density Aim

This Eastman Park Micrographics (EPM) guide explains why a density of 1.00 is used as the aim for microfilm processors and cameras and reviews basic concepts such as the characteristic curve, contrast, density and exposure.

Highlights

• As exposure increases, film density increases.
• The approximate density range of micrographic documents is 0.75 to 1.30, and 1.00 sits in the center of the curve.
• In document microfilm, D-Min and the Reference Density AIM are the most important values.
• A correct D-Min (0.03 to 0.06) ensures sufficient clarity in light areas and proper contrast.
• A Reference Density AIM close to 1.00 ensures sufficient darkness in black areas.
• These ranges are a general rule for rotary and planetary cameras and film writers, and specifications from other bodies may take precedence.
• The AIIM-MS 23 standard classifies documents into 4 groups by contrast and quality.

Description

The characteristic curve of each Kodak microfilm shows the relationship between exposure and density under given processing conditions. Contrast refers to the density range of the negative, and density refers to how dark an area is and how much light passes through it. The appropriate density level is achieved by changing the exposure at the filming stage, which allows documents with different contrast levels and colors to be captured successfully.