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Fig. 9. The 4-in. lens, showing caps, sunshade and filter.
T stops. All scales are spread with uniform spacing between stops. This has been obtained by the use of a modified L-shaped iris leaf. Iris and focusing scales either work to a common index line, or to index lines on the same axis. Locks have been provided to clamp the focusing mount at any position. All distances are measured to the focal plane.
Two types of mount are provided. For the 3-in. and shorter lenses, these are the same as previously supplied, only of a much sturdier construction, and the focusing and iris rings have been brought forward from the camera for better accessability. On these mounts, the focusing is accomplished by rotating the focusing sleeve between the lens and the mount on the camera. A key in the camera keeps the lens from rotating. The focus position is locked by the clamp screw normally provided on the camera.
For the 4-in. and longer lenses, an entirely new focusing mount has been developed, common to all three lenses. A stainless steel adapter mounts the entire assembly into the camera, and is locked in position by the camera clampscrew. The focusing action is independent of this. The key orients the lens to bring focusing and iris index
fig. 10. Rear view of 2-in. and 4-in. lenses.
marks into the operating position (Fig. 10). Stainless steel was chosen because of its high shearing modulus and its ability to withstand fatigue at the junction between the camera turret and the lens body. Further, it is electrolytically inert with the camera turret. A red dot is placed on the flange focusing seat of the adapter in direct line with the bayonet slot, which enables the easy mating of the slot and the bayonet when inserting the lens into the camera. A square aperture in the adapter which allows added internal clearance for the light beam to the corners of the
Foote and Miesse: Military-Type Lenses
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