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How to Calibrate Optical Density

Optical density is the measurement of light that is absorbed into and emitted through an object, such as refracted light through a glass prism. Photographers and medical imaging professionals measure optical density film print images with a densitometer which measures the amount of transmitted light to ensure the quality of the image. Most densitometers transmit light through an object to a photocell that records the amount of light that passes through the object. Other densitometers specialize in recording the reflection of light from solid objects where transmission can't be measured. Properly calibrating a densitometer is vital to ensuring a correct measurement of optical density.

Things You'll Need

densitometer
manufacturer's instrument calibration plaque
densitometer calibration screwdriver

Instructions

- 1
  Perform a null calibration on the densitometer by holding the "read" button down and then pressing the "null" button. This test should be performed once daily and should not be performed more than once per on/off cycle of the densitometer.
- 2
  Perform a slope calibration on the densitometer, by pressing the "read" button. Note the "CAL STEP" on the calibration plaque and compare the known optical density from the plaque to the optical density reading given by the densitometer. Continue to hold the "read" button until you know the device is properly calibrated.
- 3
  Calibrate the densitometer if the reading is outside of the margin of plus or minus .02. Locate the calibration screw on the densitometer and turn it with the screwdriver while continually holding the "read" button to bring the instrument into proper calibration. The screw should be turned clockwise for readings minus .02 and counterclockwise for readings plus .02.
- 4
  Release the "read" button once the reading on the densitometer is within the acceptable range of calibration according to the calibration plaque.

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