The B Camera

The two missions that overflew parts of Egypt in1959 both carried the so-called B camera, a technological marvel developed explicitly for high-altitude flights on the U2. It had cutting-edge optics and a sophisticated rocking system that allowed the camera to shoot at defined angles, moving through a set of positions in fairly rapid succession. Since nearly everything on the U2 was designed to minimize weight so that high altitudes could be achieved, a single camera that could achieve a panoramic sweep was much preferable to a setup with different cameras pointing in fixed different directions. The B camera was thus a major improvement on the previous A-2 camera, which had had three smaller cameras set into fixed positions. The B setup achieved the same coverage on the ground in terms of what was in the images, but the smaller A cameras had significantly lower resolution and were thus much less useful for reconnaissance (at the time) or archaeology (today).

The 850lb (386kg) B camera had a fixed focal length of 36 inches (91cm) with an f/10.0 aspheric lens. The exposed surface - equivalent to today’s sensor in a digital camera - measured 18x18 inches (46x46cm, or 460x460mm). The size of this negative can be compared to standard film from a consumer camera of the era, which was 24x36mm. The combination of lens and exposure size allowed, ideally, for resolution of objects measuring 2.5-3 feet (75-91cm) on the ground when shot from U2 cruising altitude of 70,000 feet. As the images of Egypt available here show, this resolution was often reached in practice.

As with the camera itself, the film was a new development specifically engineered to meet the requirements of high-altitude high-resolution photography. Of particular importance for understanding the images produced is the way the film rolls were mounted within the plane. The films were long and heavy, and as each click of the shutter advanced the film, over the course of a long flight the weight of the film would be moved. The extremely precise balancing of the U2 could not accommodate shifts in weight. Thus even if an 18-inch wide film had been feasible, using it within the plane would not have been. The solution was brilliant: films only half as wide as the exposure would run parallel to one another, spooling in opposite directions. At takeoff the spool of film on the right side of the plane would have its weight in the front, and the spool on the left side of the plane would have its weight in the back. Each click of the shutter advanced the spools one frame, but in different directions with respect to the body of the plane, thus with no effect on the overall balance of weight. Each click of the shutter made one image, but that image itself was split across two half-width negatives.

The combination of the rocking system moving through different positions in rotation, along with the opposed directions of the spools of film, result in rolls of negatives that are very confusing to read. Any single spool represents only half the frame of each shot. In other words, in order to see the full frame of any shot, you need to match up the halves found on two different rolls. Not only that, but adjacent images on the same roll do not show overlapping features on the ground. Adjacent shots on the roll were shot in different camera positions, and half of the frame of the shot is not on the roll, and it can be difficult to figure out the relationship between successive images. Overlap in ground coverage on a single roll rather occurs every third image, as the camera returns to the same position and shoots the next in a sequence. For this reason, canister and frame numbers are only rough guides and real engagement with the images requires georeferencing them and then accessing them through a map-based interface.

The B camera was an intermediate camera, better than the A series cameras but not yet as good as the cameras to come in the 1960s. Still, the images from these flights are of a resolution that was not bettered in practice in this area for decades. They are far sharper than images captured with the CORONA satellites, which were also using film (cannisters had to be dropped from space to be developed). Closer to the ground aerial photography could achieve higher resolution already in the 1950s, but the comprehensiveness of coverage was much more limited - for archaeological purposes, few flights were flown and those were only over known sites. Modern digital satellite imagery can achieve astonishing resolution, but most satellites that are producing commercially available imagery are only slightly better than the U2. For instance Digital Globe’s WorldView-1/2/3 series, GeoEye-1, and Airbus’s Pleiades all provide images at resolution of around 0.5m. Much of this is available through GoogleEarth. Given the extreme changes in the landscape of Egypt since 1959, the uses of this imagery are simply different than that made available here. It is the combination of resolution, coverage, and date, that make the U2 imagery so valuable.