Saturday, July 19, 2014

Prismatic Analysis

One of the projects that I've been working on is the Brashear astronomical spectroscope from 1891. We're trying to recreate the ability to record spectra using the original photographic plate holder. Here is the wooden plate holder mounted in place of the eyepiece assembly that is used for visual spectroscopy.

A focusing screen was created by mounting the ground glass in a foamcore frame that fits the plate holder.

The spectrum of sunlight at low resolution projected on the focusing screen. The dispersion is wide enough to capture the entire visible spectrum.

The spectrum of sunlight at higher resolution. The spectral lines are not visible due to the coarseness of the focusing screen.

I've been working with Photographic Historical Society of New England members Mike and John. They fabricated a Polaroid back that fits the plate holder.

There are a number of attachments that can be used with the refractor at Ladd Observatory including a Graflex Speed Graphic camera and a bifilar micrometer. Pictured here on the left is the spectroscope mounting and the eyepiece holder is on the right.

The spectroscope mounting attached to the telescope.

The next step is to take a series of Polaroid exposures to determine the optimum exposure time. We can then insert film in the original holder and record the spectrum at high resolution.

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