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From Apollo 12 Mission

The camera equipment carried by Apollo 12 consisted of one 70-millimeter Hasselblad EL camera, two Hasselblad data cameras, two 16-millimeter Maurer data acquisition cameras, one 35-millimeter lunar surface close-up stereoscopic camera, and a four-camera, multispectral S-158 experiment.

From Apollo 12 Mission; Four-Camera

Four-Camera, Lunar Multispectral S-158 Experiment. The lunar multispectral camera (LMC) experiment used four Hasselblad EL cameras. The objectives of the experiment were (1) to photograph lunar surface color variations for geologic mapping, (2) to correlate photographs with spectral reflectance of returned samples for compositon determination, (3) to photograph potential lunar landing sties, and (4) to make comparative studies of lunar reflectance variation and wavelengths. (A similar experiment was flown as the SO-65 Earth multispectral photography experiment on Apollo 9.)

The four cameras used had the same parameters, settings, and ranges as the Hasselblad EL camera with the 80-millimeter lens. The cameras were mounted in a ring bracket perpendicular to the command module hatch window ±5° from nadir, 57.5° pitched up from the X axis. The shutters were automatically tripped by an intervalometer at 20-second intervals to obtain vertical strip photography.

From Apollo 12 Lunar Photography (NSSDC ID NO. 69-099A-01) also marked Data Users' Note NSSDC 70-0:

Four-Camera, Lunar Multispectral S-158 Experiment. The lunar multispectral camera (LMC) experiment used four Hasselblad EL cameras. The objectives of the experiment were:

  1. to photograph lunar surface color variations for geologic mapping,
  2. to correlate photographs with spectral reflectance of returned samples for composition determination,
  3. to photograph potential lunar landing sites, and
  4. to make comparative studies of lunar reflectance variation and wavelengths.

(A similar experiment was flown as teh SO-65 Earth multispectral photography experiment on Apollo 9.)

The four cameras used had the same parameters, settings, and ranges as teh Hasselblad EL camera with the 80-mm lens. The cameras were mounted in a ring bracket perpendicular to the command module hatch window +/- 5° from nadir, such that they were aimed and operated simultaneously. Camera alignment was 57.5° pitched up from the X axis. The shutters were automatically tripped by an intervalometer at 20-second intervals to obtain vertical strip photography. The film/filter combinations for the cameras were:

            Film           Filter
Camera 1  B&W 3401      Photar 47B (blue)
Camera 2  B&W 3401      Photar 29 (red)
Camera 3  B&W 3401      Wratten 58 (green)
Camera 4  IRBW SO-246   Photar 87C (black)

From Apollo Image Atlas, 70mm Hasselblad Image Catalog, Apollo 9

The Apollo 9 mission cattied six 70MM cameras. Two individual cameras and a block of four cameras that made up the Lunar Multispectral Experiment. There were a total of 1373 exposures made with 2-4 images produced for each of the 159 exposures on the multispectral experiment. The number of images on 11 magazines of film was; 318 images on black & white film, 787 on color film, and 267 on infrared film.

which is followed by a list of magazines.

Question: What did the Apollo 12 multispectral Four-Camera system actually look like? Are there photos of it, how it was mounted and used during orbit?

"bonus points": what was the purpose of the "black" filter on Camera 4?

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Here is an image of the Apollo 9 multispectral camera mounted to the hatch window. It was used in Earth orbit:

enter image description here

Image from this pdf.

A color image of the array from this NASA page: Note the different color labels in green, red, brown and black.

enter image description here

An front side image of the Apollo 12 camera array was provided by Organic Marble, so I concentrate on the filter and the film.

The 87C filter is explained here in this KODAK PROFESSIONAL High-Speed Infrared Film datasheet:

If you want to record only infrared radiation, use a filter that blocks all UV and visible radiation, such as KODAK WRATTEN Gelatin Filter No. 87, 87C, or 89B. Your choice of filter depends on the photographic effect you want to create.

enter image description here

The code IRBW is explained in APOLLO 12 LUNAR PHOTOGRAPHY:

enter image description here

A photographic IR film is sensible to at least UV and visible blue light too, to get an IR image only you need a filter blocking all visible light and passing only IR radiation. This filter would look black to the eye.

enter image description here

So the array of four cameras was used from the Command Module and was fixed to the hatch window.

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    $\begingroup$ Nice! Now we see the front and back. $\endgroup$ – Organic Marble Aug 21 at 14:46
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    $\begingroup$ If the hatch window would have been a little smaller, the camera array would not fit anymore. It was important to mount the lenses of the four cameras as close as possible. So each camera had a different rotation, no problem using the square film format of the Hasselblad cameras. $\endgroup$ – Uwe Aug 21 at 14:56
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There's a picture in the Apollo Experience Report - Photographic Equipment..., page 21.

enter image description here

This is a guess really - it's out of my wheelhouse - but a note on Page 11 in the document linked above gives the experiment number SO-246 associated with this instrument, and on Page 5 in the Apollo 12 Lunar Photography document linked in the question, SO-246 is stated to use infrared film. So I speculate the black filter was for IR photography.

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    $\begingroup$ Ah, "black" = infrared makes sense. Those colors could be the visual appearance of the filter, and of course it would appear to be black in visible light. "bonus points" hereby awarded! $\endgroup$ – uhoh Aug 21 at 0:41
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    $\begingroup$ That gives new meaning to the term "four eyes". $\endgroup$ – DrSheldon Aug 21 at 1:06
  • $\begingroup$ I wonder if this was used in the CM or LM, and if they just held it up to the window for a while, or it attached to the window somehow. $\endgroup$ – uhoh Aug 21 at 5:14
  • $\begingroup$ Looks kind of similar to the JunoCam setup. $\endgroup$ – Magic Octopus Urn Aug 23 at 19:28

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