Newtonian Double-Sided Plate Holder
Accession Number: 2019.ast.229
This instrument consists of a number of roughly circular metal components on top of one another, all painted back, with a rectangular box at the top. Red and yellow wires are attached.
The base rings form an aperture and connection plate to a large telescope. Visible on the inside there are a pair of flapping shutters hinged on the outside and operated by a knob on the exterior of the instrument; behind this the plate box is visible. Above the attachment plates, there is a section of rungs which form an adjustable section; these pieces are not closely next to one another but instead ‘floating’ about half a millimeter apart, enabling adjustment. Around the exterior of these ‘floating’ rings, there are two points of adjustment, one on either side of the instrument, One of these consists of a knurled knob connected to a rod which runs beside the circular section and screws into a plate attached to an adjacent section of the ring. On the other side, there is another knurled knob; this one is attached to a knob with a scale around the circumference, which is attached to a screw rod that points directly towards the circular ring where it presses against a small circular plate. Below this, there is a spring that connects to an adjacent corner of a lower ring via a complicated mechanism which includes a small unmarked scale and an indicator arrow. There is a similar mechanism near the other knob.
The last section is the smallest in diameter and fixed to the rear of the instrument. It consists of a cylindrical section with a broader rim which is attached via heavy bolts to the rearmost floating ring. On either side of this, in the back portion, there a pair of rounded openings. One of these has a small tube with a lens in it pointing directly into the opening. This tube’s orientation is adjustable via a bracket that connects the instrument to a carriage that runs along a scale with a vernier attachment. The carriage’s movement is adjusted by a knurled knob.
On the rear of this piece, there is a rectangular box with a green sticker on it, reading “1”. A similar sticker is nearby. This box can be removed by turning a metal latch, revealing an internal box section where a photographic plate can be placed. On one side of this, there is a knob to adjust the plate holder’s position in one dimension.
Around the exterior of the instrument, there are wires. These emerge coiled together from the lens tube and then split into two pairs of red and yellow wires, one of which runs to a dial fixed to the rearmost plate. The other cable runs to a two-pronged plug.
Primary Materials: Metal: Iron Alloy, Plastic, Glass.
A label stored with the object reads: “Newtonian Double-sided Plate Holder
Sir Howard Grubb, Parsons and Company, Ltd., Newcastle-Upon-Tyne, UK
(some components are missing)”
Dimensions (cm): Height = 25, Width = 34, Length = 38.
This plate holder held a plate for the David Dunlap Observatory’s 74″ telescope.
Good: The surface paint of the instrument is chipped in places. This is especially true of the plate holder, where much of the paint is removed and the rest is chipped. On other parts of the instrument, the paint is only removed on the edges and corners of the instrument. The instrument is not very rusty; there is some rust on some components, including the plate that supports the scale and knob attached to the microscope, the spring attached to the knob on the floating section and some of the other screws and attachment components for the wires.
The adjustment knobs are in fair condition, although screws that were oiled are craked with dust in the oil. Plastic components are yellowed, although not cracked. Wire insulation is in good condition.
According to a label with the object, some components are missing.
Parsons & Company, Ltd., Newcastle-Upon-Tyne, UK
Date of Manufacture: c. 1930-1935
This plate holder was used with the David Dunlap Observatory’s 74″ telescope. Following going out of use, it was stored at the Observatory until the Observatory’s sale in 2009, when it was moved to the University of Toronto’s Department of Astronomy & Astrophysics at the St George Campus. In 2017 it was moved to a new storage location in McLennan Physical Laboratories.