The 1850 was the first commercially available camera tube, introduced in 1938 by RCA. It was used in studio cameras through World War Two and in film chains into the 50s. Here is the specification sheet for this tube (courtesy of Troy Walters.
A smaller version, the 1848, was introduced in 1939, and was used in field cameras. The 1846 was made in the early 40s for use in military cameras.
C7373A developmental iconoscope made in 1938. This appears to be a pre-production version of the 1850
(donated by Dick Malm)
Here are Dick's recollection of the history of this tube: