Trial Frame of Burchard 1895 | Brass PD

The Trial Frame of Burchard 1895 dates to around 1895. It has room for one lens in front and one in the rear. The interpupillary distance is adjustable. This adjustment works binocularly, meaning both sides move together at once.

Design Origins

The very first trial lens frames appeared in the late 1800s. Early versions had a lower half that held one loose lens. A spring-like clip above held that lens in place. Over time this design evolved. Later frames held two lenses on the same side. Their cylindric lens could rotate too, adding more flexibility during testing.

Construction and Adjustment

This frame follows the Burchard style from 1895. It has a brass frame with a spring clip in the rear. That clip holds the spherical lens in place. A separate spring clip on the front holds the cylinder lens. Two rounded protrusions sit on the front. These let the examiner rotate the cylinder axis to the desired degree. Degrees are marked off on white arcuate parts on top of the front. In this example, the left arcuate part is missing, covering 105 to 180 degrees.

Pupillary Distance Mechanism

A long screw controls the pupillary distance. It changes the lens separation on both sides at the same time. This differs from today’s trial frames. Modern frames allow one-sided pupil distance adjustments instead. The temple pieces use straight wire, common on eyewear throughout the late 1800s.

A Historic Design Precursor

This Burchard Trial Frame offers a clear look at binocular PD adjustment, a design choice later replaced by more flexible one-sided systems. Collectors tracing the evolution of refraction testing tools will find it a useful counterpoint to the Nachet trial frame elsewhere in the collection, which predates this Burchard-style design.

Short Description

This 1895 Burchard trial frame has a brass build with binocular pupillary distance adjustment via a single long screw. It holds both spherical and cylinder lenses, contrasting with later one-sided refraction frame designs.