28MM SCREW MOUNT LENSES

2.8cm f/6.3 Hektor

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Max Berek was responsible for the development of lens^121. The 5-glass design of triplet configuration was introduced in May of 1935¹²¹. The optical design of this lens features an enlarged front element, resulting in good central resolution at all apertures and excellent peripheral performance when stopped down to f/11 or less. The use of special formula glass and a unique, patented banana-shaped iris diaphragm leaf enhanced its optical performance¹²¹.

The hyperfocal distance at f/6.3 was 12 feet. This meant that setting the focusing scale to 12 feet will result in everything from 6 feet to infinity to be in sharp focus. While the maximum aperture of f/6.3 might seemed slow, it represented an impressive achievement in lens design, especially when one considered its angle of view at full aperture. The lens had a field of view of 76 degrees diagonally, with a vertical angle of view of 46 degrees and a horizontal angle of 65 degrees, based on a 24 x 36mm image size³⁵⁸.

The lens weighted 100 grams¹²¹. and featured continental f-stops (ranging from 6.3 to 25)¹²¹.The lens was compatible with 36mm (A36) push-on or 34mm screw-in filters. The rotating lens mount could focus as close as 1 meter. Distance scales were available in both feet and meters¹²¹.

Some lenses were supplied in a tin tropical case¹²¹.

Coated lenses appeared in the 580XXX batch from 1941. Whether these represent wartime or postwar production is still debated, as Leitz often issued lenses with pre- or wartime numbers in coated form to fill out incomplete serial number batches. Further research is required to resolve this issue.  Routine coating of Leitz lenses began in November 1945¹²¹.

Variants

There are 3 variants of this lens³⁶⁰:

• Variant 1 comes with the serial number engraved around the mount of the rear elements³⁶⁰. In order to see what the number was, one had to remove the lens from the body³⁶⁰. This variant has nickel finish³⁶⁰. Production of the rare nickel finish version ceased in 1937¹²¹. Nickel versions are only found in 250XXX and 273XXX batches³⁶⁰.  No more than 200 lenses had nickel finish¹²¹.  Code-named HOOPY⁸².
• Variant 2 is similar to Variant 1, but has chrome finish³⁶⁰. The production of this variant started in 1936³⁶⁰. The chrome version continued until production was halted by the war in 1942¹²¹. Reported serial number batches include 250XXX, 273XXX, 336XXX, 425XXX, and 580XXX¹²¹. Approximately 8037 lenses of this variant were made¹²¹. Code-named HOOPY-CHROM¹²¹.
• Variant 3 comes with a new international aperture scale³⁶⁰. The serial number is located on the ring around the front element of the lens³⁶⁰. The lens comes in chrome finish³⁶⁰. The lens was discontinued in 1952³⁶⁰. The relatively rare postwar model, known as HOOPY-B (the "B" stands for Blau, or coated), remained in production until July 1952 and was produced in one serial number batch, 790101-791557. All of these lenses featured rotary chrome mounts similar to the prewar version, used international f-stops (6.3-22), and were coated. Minor variations exist; one version has the serial number engraved on the front in very fine letters, which are occasionally found on the prewar model¹²¹. Approximately 1457 lenses of this variant were produced¹²¹.

Accessories

Viewfinders

Viewfinders available for the lens: The folding bright line sports finder was available in black (SUOOQ) or chrome (SUOOQ CHROM) finish from 1934 to 1940, though no parallax correction was provided. A 50mm reflecting waist-level finder (AHOOT) was supplied in black with a swinging negative front lens to convert to the 28mm field of view. In 1940, the Imarect universal viewfinder with the TUVOO 28mm adapter was introduced at the Leipzig Fair. TUVOO remained in production until 1963, with only minor changes in engraving. Ernst Leitz, New York manufactured a version called VIOAD from 1941 to 1949 for their iteration of the Imarect, known as IMFIN¹²¹.

Lens hoods

Lens hoods available for the lens: In 1934, a push-on, clamping, black round lens hood (SOOHN) was introduced with nickel fittings and metal-filled engraving. These were quickly replaced with chrome set screw hoods and paint-filled engravings. The hood was copied by Ernst Leitz, New York, during 1941-1949 in two versions¹²¹:

• one with a flat black interior and a dull brushed chrome exterior¹²¹
• the other with glossy black replacing the chrome exterior¹²¹

A close comparison of the Ernst Leitz, New York hoods with the Wetzlar version reveals only slight differences in the chamfer along the rim of the shade¹²¹.

Today, SOOHN hoods are more difficult to acquire than the lens itself¹²¹.

Military

It is known that coated lenses engraved with the Reichsadler were supplied to the Kriegsmarine¹²¹.