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CCD Sensor used in Dunlap Observatory Cassegrain Spectrograph

This instrument is an electrical assembly supporting a silicon sensor charge-coupled device. It consists of a metal base and two plastic circuit boards mounted on top of each other, with the upper piece containing the main component – the silicon sensor. The beige circuit boards are stacked about a 4cm apart and are attached using a series of metal columns, which are affixed using metal screws, and by very thin metal wires protected by plastic tubes.

There are two larger black PVC insulated wires connecting the upper circuit board to the CCD sensor. The sensor is framed by a yellow and seafoam green ceramic package. The entire unit is screwed to a larger metal plate underneath, likely used as a mount. There is a bundle of copper wires protruding through a hole in the centre of the plate. They are soldered to a copper square with a central hole. There are various electrical components attached to the circuit board, including resistors, capacitors, and a low noise amplifier.

Accession Number: 2022.ast.286

Alternative Name: Charge-coupled device

Primary Materials:

Iron Alloy, Copper Alloy, PVC, Silicon, Ceramic


On steel mount:
“126 AP FALF” (carved)
On bottommost circuit board:
“DDO” (carved)
“PCB 2700004 REV.G ASSY. 0100025– REV. S/N” (etched)
“S88” (carved)
On microchip mounted to bottommost circuit board:
“S NE5534AN QFP3857 8749VH”
On resistor mounted to bottommost circuit board:
On capacitor mounted to bottommost circuit board:
On upper circuit board:
“DDO 22” (carved)
“ASSY # 0100172 REV S/N 22 TH1K PCB 2700092 REV –” (etched)

Dimensions (cm): Height = 9, Width 12.5, Length = 8.5


CCDs are used as a modern replacement to a photographic plate. They work by employing the photoelectric effect. When a photon that has entered the telescope hits an electron on the silicon sensor with enough energy, the transfer of energy be sufficient to liberate the electron from the silicon atom altogether. A capacitor that lies underneath then collects electrons and translates the data to an electrical signal. CCDs are used in imaging, photometry, and spectroscopy. In spectroscopy, light enters the spectrometer, is then collimated by collimating optics, and then dispersed by one or more diffraction gratings, before being focused onto the CCD detector. Information from the detector is then sent to a computer for analysis.Because CCDs are so sensitive, they must be cooled as to reduce or eliminate noise caused by heat exposure. This CCD was cooled using a liquid-nitrogen cooling system. CCDs can also have coatings that increase their electromagnetic range. For instance, an ultra-violent enhancement coating converts UV photons into long-er wavelength photons. It is unclear whether this CCD has an enhancement coating.


The overall condition of the system is excellent. The photosensitive surface and circuitry have no obvious signs of damage. There are some superficial scratches on the metal mount, though they are merely cosmetic. There is some wear on one edge of the top of the upper circuit board, though it does not seem like it would affect functionality.

Associated Instruments:

Manufacturer: Thomson/Photometrics (Likely)

Date of Manufacture: Early 1990s (Estimated)


This instrument was donated by Dunlap Institute Associate Professor Dr. Suresh Sivanandam in September of 2018.

Historical Notes:

Used in conjunction with the 74” telescope at the David Dunlap Observatory, this CCD was used as a detector in a spectrograph, likely Echelle, mounted in the broken Cassegrain configuration. In this configuration, light enters the telescope, is then reflected by the primary mirror onto the secondary mirror, then reflected back down through a hole in the primary mirror, and finally “broken” by a third mirror (which is normally folded up inside), diverting the path to an Echelle spectrograph mounted near the base. This CCD is likely one of the three Thomson/Photometrics THX31156 detectors that were used prior – about 2003-2004. See link under “Additional Information and References” for THX#1, THX#2, and THX#3.

Because it is unclear which of the three CCDs this artifact is, there are different possible reasons for its retirement. It may have been retired upon the purchase of a new, more modern Jobin-Yvon CCD. It may have also been replaced after having been damaged by a power surge. While there is no physical indication of this, it is not uncommon for CCDs of this era to have been damaged this way. Very small unwanted electrical voltages, which would leave no marks at all, can cause malfunction. Even static electricity generated by contact by technicians can interfere with a CCD’s performance. Technicians must take precaution, wearing anti-static clothing and bracelets connected to the laboratory ground.

As this CCD was used with the Echelle spectrograph, which contained two diffraction gratings, its spectral resolution was higher than that of the alternate Cassegrain spectrograph. Professor Slavek Rucinski explains, “But a higher resolution means that fewer photons are registered per a resolution element (or detector pixel). This limits the range of observable objects with the [Echelle spectrograph] to only bright stars. In our case these were stars brighter than about 5 – 6th magnitude. Our [Cassegrain Spectrograph] permitted observations of fainter objects, to about 10-12 mag, but at a much lower spectral resolution. The research goals are normally the main driver for selection of a specific spectrograph, depending [on] what is more important: the spectral resolution or the faintness of accessible objects.”

Thanks to Professor Slavek Rucinski for this information.



  • Donated to UTSIC