Hasselblad (Ross) SKa 4

The SKa 4 was the Swedish Air Force’s second order from Ross AB, and a different kind of camera from the first. Chernoff’s account on Hasselblad Historical has the Air Force’s photo interpreters, satisfied with the hand-held HK 7, asking Victor Hasselblad late in 1941 for a camera to be mounted rigidly in an aircraft’s belly with its lens axis vertical and a larger frame — one that would give the registration needed for mapping and, flown at constant height and heading with about 60 per cent overlap, for stereoscopic interpretation. Hasselblad’s own history page puts the commission at the end of 1941. Chernoff says the Ross crew designed and built it within several months, so the first cameras belong to 1942, and his summary table runs the model to “1943 ?”. The designation is Flygseriekamera SKa 4 — a series camera, as against the HK 7’s Handkamera — and SK stands for spaningskamera, reconnaissance camera.

Its layout is unlike anything Hasselblad made afterwards. The 12×12cm frame — Chernoff calls the format unusual, 4.7 inches square — sits on special 130mm-wide double-perforated film, 200 exposures to a cassette, in interchangeable backs: the first on any Hasselblad, the feature the 1951 company brochure wrongly credited to all 342 wartime cameras. An electric motor, cabled to the aircraft’s DC supply or a battery, advances the film and cocks the shutter, and an intervalometer sets the spacing; the date, hour and minute of each exposure are stamped on the film edge. The lens system was three-tiered. A Zeiss Tessar 15cm f/4.5 was mounted permanently inside the body and folded aside when a bayonet lens was fitted; when the internal lens was in use, a clear glass or filter had to be fitted in the empty bayonet. The bayonet took a Zeiss Tele-Tessar 25cm f/3.5, a Meyer Tele-Megor 40cm f/5.5 and, per the summary table, a Zeiss Tele-Tessar 50cm f/5.6; a Cooke Aviar 15.2cm f/4.5 is also listed — the only British lens on any Ross camera, and unexplained. All were fixed at infinity and uncoated. The shutter is the Ross behind-the-lens leaf type at 1/75, 1/150 and 1/300; SKa 4a no. 51 has five leaves.

The camera is heavy: 50 × 38 × 24cm and 14.9kg with the 15cm lens, on Chernoff’s figures, with the aircraft mounting frame adding 6.2kg. The frame is itself an instrument — the lens collar sits in a ring that tilts side to side inside a square holder that tilts fore and aft, so the axis can be set truly vertical, and the camera rotates in the ring to correct for crab in a crosswind. A telescope-like magnifying finder, attached by an oversized accessory shoe, projected through a port in the floor. Two wooden side handles allowed the camera to be lifted out and hand-held, though at this weight Chernoff doubts it often was. The SKa 4a is the same camera without the fold-away Tessar: bayonet only, and — on the Göteborgs Stadsmuseum’s measurements, which Chernoff passes on with a warning — 28.5cm long and 10.4kg, the 21.5cm saved being the spacer section that housed the internal lens. Chernoff dates it 1943 to 1945 and can give neither a count nor a serial range; he suspects the 70 in his table, formally the SKa 4’s figure, covers both models, and that 4a serials were interspersed with the 4’s. Whether numbering began at 1 or, like the MK 80’s, at 101 he leaves open. The Flygvapenmuseum holds a “Flygkamera SKA 4” in its transport box.

What the SKa 4 contributed outlasted the camera. Chernoff draws the line explicitly: the interchangeable back became the magazine of every V-system body, the integrated motor became the drive of the 500EL and its successors, including the NASA electric data cameras, and the auxiliary magnifying finder foreshadows the sports and magnifying finders of the commercial line. What remains unknown is nearly everything an owner would want — the aperture ranges of the lenses (Chernoff marks all of them “information requested”), the film flattener’s design, the true production split between SKa 4 and 4a, the end of SKa 4 production, the aircraft types that carried it, and the source of the Cooke Aviar. Afalter’s 1993 book gives the standard lens as a 105mm Tessar, which Chernoff reads as a misprint for 150; no source has since confirmed either.