Nagel Anomaloscope Model 1 (c. 1907)

The Nagel Anomaloscope Model 1 is considered the absolute "gold standard" medical instrument used by doctors to precisely diagnose and classify red-green color blindness. Invented by a German scientist in 1907, the device was developed to provide a rigorous, foolproof scientific evaluation that was far more accurate than simple printed color cards. When a person looks into the viewing eyepiece, they see a circular screen split perfectly into two halves:

• The Bottom Half: A pure, built-in yellow light that the doctor can make brighter or dimmer.

• The Top Half: A customizable mixture of red and green light that the patient can adjust using dials.

The test requires the patient to turn the dials to mix the red and green light together until the top half perfectly matches the shade of yellow on the bottom half. By analyzing the exact mathematical ratio of red to green a person needs to see a perfect match, eye doctors can easily map out precisely what type of color blindness a patient has. Although production of this classic mechanical model wrapped up in 1983, it remains the definitive clinical tool used by researchers around the world to study how humans perceive color.

Sourced from: Elephants Trunk Flea Market