M19 7x50
Mfr: Bell & Howell, Chicago, USA
Date: circa 1976
AFOV: ~51 degrees
Eye Relief: ~20mm
Objective: 3 element f/3, 150mm focal length
Eyepiece: 6 element Erfle type, 22mm focal length
The M19, made for the US Army, is an unusual binocular. It employs a modular design, with interchangeable, pre-collimated, parts intended to simplify field servicing. The prism cluster is collimated in the factory using a reference jig and then cemented together. The objective and eyepiece assemblies are precision made to maintain collimation. Unfortunately, for the collector or hobbyist, this means that this binocular is not really serviceable. If you have a M19 that is out of collimation, you can try removing and remounting the prism clusters and hope that fixes it. Otherwise, you will have to find spare parts or scavenge from another set. The other feature of the M19 is that it is considerably smaller and lighter (34 vs. ~50 ounces) than the usual military 7x50.
Below: the M19 along side a B&L 7x50.
The optical design of the M19 is also unusual. It employs a 3 element airspaced telephoto type objective to reduce the focal length and thus the size of the binocular. The low f/3 focal ratio allowed the use of smaller prisms than usual , which were also made asymmetrical to further cut weight. However, the low focal ratio required a complex 6 element eyepiece for good correction. The Erfle type eyepiece is normally only found in wide angle designs, not the modest 50 degrees or so for the M19. In addition, the M19 employs a plano concave field flattener near the eyepiece which doubles as a reticle on one side. Field flatteners are rarely found in military handheld binoculars. The M19 is one of the few binoculars I have seen that produces an image nearly in focus from the center all the way to the edge of the field. One place the designers skimped on the M19, though, is in baffling. The prisms don't have any shielding and one can see areas of light leakage when looking through the eyepieces. Perhaps this was a tradeoff to save weight.
Below: left, the tiny prism cluster, right, the reticle/field flattener (only the military would see the need for the "BNCLR" mark, perhaps to remind clueless foot soldiers).
Although the M19 was introduced into service in the 1970's, the design actually dates further back. In the late 1950's, the Frankford Arsenal and the Farrand Optical Company collaborated to design the T14, the prototype to the M19. After field tests, the design was modified (mainly mechanical improvements, I believe) and eventually Bell & Howell secured the contract to produce the M19 for the US Army. I don't know if the M19 can be regarded as a success. The binocular must have been expensive to manufacture and resulted in many damaged parts that were thrown away. Although superseded by the M22, I believe the M19 is still being used in the field (I have seen Army National Guard troops using the M19 in 2002). Although most M19's are finished in a greenish-gray color, there are some examples of the same binocular finished in black, possibly for the US Navy.