AGFA Duoscan T2500

High resolution scanner for negatives, slides and prints running on a Macintosh G3 with Photoshop 5.5 as the graphics program or Fotolook for batch processing.

However, the demand for scanning blots is such that we provide these supplemental data. Only dry blots and laminated gels may be used with the scanner.

We highly recommend that you have standards on each autorad or other gel/blot that you scan. This way you can compare to a known standard directly or fit to a polynomial to correct for nonlinearities.

Regardless, we scanned neutral density filters of known value and found that the % transmission^* as rated on the filters is roughly linearly related to the mean pixel intensity as measured.

The filters were purchased from Omega Optical and from Chroma Technology. The intensity values were measured in IP Lab and checked with the histogram function in Adobe Photoshop. [In the image below, the gray scale values have been changed for presentation via the web.]

The graphs above do not go to black. The graph below uses the ring around the ND 0.5 filter as the measurement of 0.00% transmission.

The formula used is:

optical density (OD): For a given wavelength, an expression of the transmittance of an optical element. Optical density is expressed by log₁₀(1/T ) where T is transmittance. The higher the optical density, the lower the transmittance. (Optical density times 10 is equal to transmission loss expressed in decibels, e.g. , an optical density of 0.3 corresponds to a transmission loss of 3 dB.)

Based on this definition, we say that T = 1/10^D where D is the optical density.