Biotessar 13.5cm f/2.8 (HK 7)
Carl Zeiss · Hasselblad Ross · 1941 · Biotessar
single source, unconfirmedAlso known as: Biotessar 13.5cm f/2.8 (HK 7) · Ross HK 7 135mm
Variants & identification
| Variant | Mount | Years | Serial ranges | Production |
|---|---|---|---|---|
| HK 7 bayonet | Ross HK 7 (its own bayonet — hand-fitted to one camera) | 1941 | — | — |
- No serial list has been published for the HK 7 lenses as a group, and none for this Biotessar in particular. What exists is the general Carl Zeiss Jena sequence, which covers the lens only in the sense that it covers every Jena lens of the period.
- The Jena year boundaries above are given identically by camera-wiki and by Craig Camera's table; camera-wiki additionally supplies the 1940 and 1942 rows, which Craig Camera leaves as 'Unknown' and '2799599–' respectively.
- Both published copies of the Jena sequence stop at 1942 and resume at 1945, so there is no serial-to-year mapping at all for 1943 and 1944. Ross went on building HK 7s through the war, and a lens from those two years cannot be dated by serial by any published means.
How to tell them apart
- Bought in from Germany during the war — Ross built the bodies and the shutters in Göteborg but made no glass
HK 7 bayonet:
- Uncoated: Ross fitted no anti-reflection coating to any of its lenses
- The protective barrel is engraved with the serial number of the camera it was fitted to — mounts were hand-tuned individually, so a lens does not necessarily fit another body of the same model
Serial-range notes
- 2678326–2790346
- The rule, if the lens carries a Carl Zeiss number of its own: pre-war Jena lenses are dated from the published Jena serial list, and 1941 — the year given for this lens — runs 2,678,326 to 2,790,346. The neighbouring years are 2,652,000–2,678,000 for 1940 and 2,800,000–2,900,000 for 1942, so a number in the high 2.6 to 2.9 million band is consistent with the year this lens is dated to and the two either side of it.
- the number engraved on the protective barrel
- Not a Zeiss number and not a date. Ross hand-fitted each mount to one camera and engraved that camera's serial on the barrel, so the number most visible on a loose HK 7 lens is the body's. Read against the Carl Zeiss Jena list it will return a year that means nothing about this lens.
- any Jena serial, as a date
- Treat the Jena list as approximate. Thiele's reconstruction of the factory records shows numbers assigned to a batch when the batch was ordered rather than when it was finished, so batches were completed out of order — 1944 work carries numbers reserved for 1940, and many 1941 numbers run higher than 1945 ones. The list gives a period, not a build date.
Specifications
- Formula
- Biotessar
- Aperture range
- f/2.8
- Country
- Germany
- Coating
- None — uncoated
What reviewers say
No reviews aggregated yet — this family is still in the research queue. Written one? We'd love to index it.
History
The standard lens of the HK 7, the aerial hand camera Victor Hasselblad built to better the German HK 12.5cm that the Swedish air force had captured and asked him to copy. Ross Aktiebolag of Göteborg was the company Victor Hasselblad ran through the war, building aerial cameras for the Swedish air force, and it is where the firm that later made the 1600F learned its trade. Ross built the bodies and, unusually, the shutters; it made no glass at all. The lenses came from Germany — Zeiss, Schneider and Hugo Meyer — and Hasselblad Historical notes that no documentation has been found describing how they were imported into a neutral country that badly needed optics and rather more badly needed to be left alone.
The Biotessar is Zeiss’s fast plate-camera design of the 1930s, and at f/2.8 on a 7×9cm format it was chosen for the same reason a war photographer chooses a fast lens: aerial work over Sweden meant grey light, a moving aircraft and no second attempt. Hasselblad’s own contribution to that problem was mechanical rather than optical — he put the shutter behind the lens to cut the distortion that a focal-plane blind produces at aircraft speeds, and he made the lenses interchangeable so a crew could match focal length to altitude and route.
The camera weighs 4.8kg with this lens fitted, which gives some sense of the scale of the thing. Nothing Ross fitted was anti-reflection coated; coating reached Swedish military optics after the war, and these lenses date from before it.
One habit of the Ross shop matters to anyone who finds one of these lenses loose. The mounts were hand-tuned to fit a particular camera, and the protective barrel was then engraved with that camera’s serial number. A lens from one body will not necessarily seat correctly on another of the same model, which is why these are worth far more still attached to the camera they were fitted to than separated from it.
Hasselblad Historical’s account of the Ross cameras is the only substantial source on them, and its author marks several specifications as information requested — an open call to readers for detail he does not have. Maximum aperture, weight, element count and production quantities for this lens are among the figures that no published source gives, so what is recorded here is deliberately short.
This history is AI-written, from the sources listed at the foot of the page. Where the record is silent it says so rather than filling the gap — but no human wrote these sentences.
Example photos
Sample photo wanted — shot with a Biotessar 13.5cm f/2.8 (HK 7)? We'd love to feature it (with credit).
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