Apollo photography: Image quality
This page should be moved to the Apollo Flight Journal. (excerpts) by Jay Windley, clavius.org
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[edit] Point and shoot
[edit] The Hasselblad cameras didn't have viewfinders, automatic exposure, or automatic focus. How were the astronauts able to get any good photographs at all?
Believe it or not, people were able to take good photographs before automatic exposure computers and automatic focus devices were invented. It required a bit of training and practice. Film manufacturers commonly provide exposure guides giving the average correct camera settings for common lighting conditions.
 F-stop decal on the top of the Apollo 11 film magazine on display in the Smithsonian's National Air and Space Museum's Apollo Gallery. Photo: Eric Long (Apollo Lunar Surface Journal) |
The exposures were worked out ahead of time based on experimentation. The ASA/ISO rating of the film was known, and NASA photographers precomputed the necessary exposures. These figures were refined over the course of the program. In many cases the camera settings for planned photos were given in the astronauts' cuff checklists. In other cases the astronauts followed some basic rules.
Automatic exposure controls were available on several consumer camera models during the late 1960s. Apollo 11 Command Module Pilot Michael Collins suggested that Hasselblad look into the possibility of incorporating this technology into the camera after his experience on Apollo 11. Apparently the professional photographers who used the Hasselblad model upon which the lunar surface cameras were based did not want automatic exposure controls on their cameras and so it was not a standard feature.
Shutter speeds were typically 1/125 or 1/250 second. F-stop settings varied from f/5.6 for up-sun photos to f/8 and f/11 for cross-sun and down-sun photos.
The lack of viewfinder was occasionally a problem. Early missions used a wide-angle lens. It was sufficient to point the camera in the general direction of the subject and you would be likely to frame it well enough. On later missions a 500mm telephoto lens was also taken, and the cameras were modified with sighting rings to help aim them. Normally the camera would be mounted on the space suit chest bracket, but for telephoto use the astronaut would have to remove it and hold it at eye level in order to sight down the rings.
[edit] Focusing in the zone
 Cutaway drawing of Hasselblad EL Lunar Data camera (click for full-sized drawing). Inset shows frame counter, enlarged from this drawing, and from a closeup of a Hasselblad EC. Credit: Apollo Chronology - Photographier sur la lune |
Manual focus is not as problematic as many suppose. Lens manufacturers mark the expected distance to the subject on the focus ring, and it's simply a matter of measuring or estimating the distance from the lens to the subject and setting the ring for that value.
To aid the astronauts in measuring the distance to subject, length of commonly used tools was marked on the lens. Several Apollo photographs show the tongs and scoops used as distance references. Focus need not be exact either.
The Apollo astronauts were trained in "zone focusing", a technique used by photojournalists and sports photographers who often don't have the time to focus visually or by measurement.
At a high f-stop, a camera's depth of field increases. This means that when the lens is set to focus at a certain distance, objects somewhat nearer and farther from this ideal distance are also sharply focused. The narrower the aperture (i.e., the higher the f-stop), the greater the depth of field. And the sloppier the photographer can be be about his focus setting.
The Zeiss Biogon lens used by the astronauts had an indicator that specified the near and far boundaries of the depth of field for each combination of focus and f-stop.
Zone focusing is a technique whereby the f-stop is kept high, resulting in lenient depths of field. The focus range is then divided into "zones" corresponding approximately to near, medium, and far. These zones of clear focus overlap slightly and correspond to preset positions of the focus ring.
The Zeiss Biogon lens provided to the astronauts had "detents" or click-stops that corresponded to these three zones. The astronaut had simply to push the tab on the focus ring to one of three easy-to-find stops to select the focus zone depending on the rough distance to the subject.
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