Trial frame by Nachet of Paris predates the style of Burchard. It is estimated to be from around 1890. It was made by the famous microscope maker, Nachet, (Nachet et fils) in Paris. It consists of a brass frame with a spring clip in the rear to hold the spherical lens. In the front it has a spring clip to hold the cylinder lens. There are two rounded protrusions on the front to allow the examiner to rotate the cylinder axis to the desired degree setting.The very first trial lens frame first came along in the latter part of the 1800′s. It consisted of a lower half that could hold a loose lens. The loose lens was then held in place by a spring-like clip above. Over time this evolved to the ability to hold two lenses on the same side with the cylindric lens being able to be rotated.
The degrees are marked on the thin arcuate brass strip on top of the front.
One controls the pupillary distance by manually sliding the lens holder position over each eye. This allows for one-sided pupil distance adjustments.
The temple pieces are the straight wire type common in the late 1800′s.