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The Lex is a Japanese leaf shutter made by Mars in the late 1930s and early 1940s. It was called Pladon at an early stage. It is in #0 size, has no self-timer and is intended for use with a body release.

Pladon and Lex (T, B, 1–200)

The Pladon (T, B, 1–200) was advertised around 1937 on the Reex 6×9cm folder.[1] It has a black shutter plate, presumably inscribed Patents–Pending at the top and PLADON at the bottom, and has a round PL logo on the right. The aperture scale is attached to the bottom, and there is a rather long release lever on the side.

The Lex appears with T, B, 1–200 speeds on surviving Reex cameras — "Reex" and "Lex" may be pronounced about the same by a Japanese speaker, and this is perhaps not a coincidence. It has the same features as the Pladon, including the specific release lever. It only differs by the newer design of the shutter plate, with metal stripes on both sides of the lens. The Patents–Pending marking and the PL logo are similar, and only and the name at the bottom has changed. (On at least one particular camera, the aperture scale is reportedly covering another, directly inscribed on the shutter plate itself.)[2]

Lex (T, B, 5–200)

Other Lex shutters, giving T, B, 5–200 speeds, have been observed on a Weha Six,[3] a Loyal,[4] a Semi Kinka[5] a Nissan New Semi Condor folders (セミコンドル) [6] and maybe a Semi Proud II.[7] They have no PL logo, and the words Patents–Pending at the top are replaced by the company name Mars Tokyo and an index for the front-cell focusing lens. The aperture scale is directly inscribed at the bottom, under the shutter name.

The Lex shutter was also offered on the Semi Rosen III in 1940 and on the Roavic (5–200) in 1942.[8]


  1. Undated leaflet presenting various cameras including the Reex.
  2. Yokogawa, p.74 of Kurashikku Kamera Senka no.53.
  3. Example pictured in Sugiyama, item 1266.
  4. Example observed in an online auction.
  5. Example pictured in the page on the Semi Kinka.
  6. For walkaround of that camera, see this flickr album.
  7. Example observed in an online auction, shutter name unconfirmed.
  8. Semi Rosen III: column in Asahi Camera April 1940, pp.705–6, mentioned in Kokusan kamera no rekishi, p.343. — Roavic: advertisement dated February 1942, reproduced in Kokusan kamera no rekishi, p.105. In both cases, the shutter is called レックス in katakana only.