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Optical Passband Filters for Photoelectric Photometer


These are two similar rectangular metal pieces with a row of eight circular openings along their length, grouped at one end of the rectangle. Each of the openings has a brass threaded interior. Screwed into all the openings on 2019.ast.264.1 and six of the openings on 2019.ast.264.2 are circular differently-coloured glass filters mounted in brass surround. Aligned with each opening there is an indentation along one side of the rectangular metal piece.

Affixed by screws at one end of both of these metal pieces there is a small metal attachment that has a solid section that sticks out above the main metal section.

Accession Number: 2019.ast.264.1-2

Alternative Name:

Primary Materials:

Metal: Iron Alloy, Metal: Copper Alloy, Glass.


2019.ast.264.1: Engraved at the end of the main metal piece, by the brass attachment: “B”

2019.ast.264.2: Engraved at the end of the main metal piece, by the brass attachment: “H”

Dimensions (cm):

Both: Height = 1.5, Width = 7, Length = 33.


These are very likely optical bandpass filters for a photoelectric photometer, possibly one constructed by department professor Don Fernie. They would have been used in spectroscopy. In astronomical photometry, light is directed through filters like these, and the resulting wavelengths of emitted light is recorded with a photosensitive component. Standardized sets of filters are employed so results can be compared between instruments, and there are many possible filters that can be used, many of which may be represented here.
One standard system of “passband” optical filters is the UBV or Johnson-Morgan photometric system. In this, UBV stands for “Ultraviolet, Blue, Visual”. This may correspond with the three first filters in the 2019.ast.264.1 strip which appear yellow (visual), blue (blue) and deep purple (ultraviolet).
The filters would be slid into the photometer using the handle at the end of the strip. The cutout wedges above each inset filter ensures the strip is perfectly aligned so light passes directly through the filter. The empty holes in 2019.ast.264.2 would permit all the light to pass through unfiltered.


Very Good: The surface of the silver metal is patchily oxidized and dulled along its length, and covered in fine scratches. There are striations along both larger faces and one narrow face of the rectangular metal pieces, suggesting the instrument has been repeatedly slid into a slot. The brass sections are dulled but in good condition.

Associated Instruments:


Locally made, possibly by Professor Don Fernie and technicians at the David Dunlap Observatory.

Date of Manufacture: c. 1950


This artifact was collected from a room marked “Instrument Room” on the 15th story of the McLennan Physical Laboratory, U of T in November 2019, along with two other objects (2019.ast.264.1-2). Prior to its collection, its history is unknown, but it was likely constructed for use at the David Dunlap Observatory in Richmond Hill.

Additional Information and References:

In an interview on March 11, 2021, Professor Emeritus John Percy discussed these filters:
“[W]hen you’re using a photoelectric photometer, in order to standardize the wavelengths that you’re working at, you always have one or more colour filters that you can put in the light path. The standard ones are called “UBV” and that stands for “Ultraviolet Blue Visual” – visual is yellow. But you could also add on a red or infrared as well… If this was one of Don Fernie’s photometers, then he would have a way that you could slide in anything from three to six colour filters which would admit a very specific range of wavelengths to be measured by the photometer… [2019.ast.264.1] looks like visual on the left, blue on the second left, probably violet on the third left and I don’t know what the other ones are. The one on the extreme right is probably empty, just a way of putting all of the light through the filter… This little handle on the bottom right was used to slide it [into the photometer]. But the other thing is you’ll notice above the filters there’s an indent above each one, and that’s to make sure that it’s exactly locked in the position that it’s supposed to be in so that the filter would be exactly in the middle of the light path.”

Some of the photometers made by Professor Don Fernie for use at the David Dunlap Observatory are held by the Canada Science and Technology Museum, in Ottawa: 2008.0197.002, 2008.0197.001. These components may belong to one of those photometers, or an earlier model.
John Percy was interviewed on March 11, 2021.

Historical Notes: