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frame is positioned by taking advantage of the slot.
The focusing jacket deserves special comment. Because of the weight of the lenses, a sturdy mount is required (Fig. 11). The focusing threads are nominally square, but the sides have a few degrees taper for ease of manufacturing, and to provide a good fit. They have been perfection-lapped with special noncharging compounds in order to maintain smooth operation and long life at all temperatures.
The outer sleeve is made in two separated sections, spring loaded for accurate positioning. The focusing lock, when applied, operates in the same direction as the loaded spring; thus, a rigid, exact station of focus is acquired. When the knurled lock ring behind the focusing ring is turned, the floating section of the sleeve is pushed away from the main stationary section, clamping the threads axially on the internal sleeve or screw.
These lenses are all flange focused on an internal flange. Consequently, there is no defacing of any outside surfaces. The trimming dimension is held within plus or minus 1/20 of 1%, to plus or minus 1/33 of 1%, depending on the particular focal length of the lens in the series. Special equipment had to be designed in order to measure and maintain these very close dimensions.
Provision has been made to add Depth of Field Scales when required.
A new design dust cap is provided (Table II). It is black molded coldresistant synthetic rubber with a metal insert, giving the stiffness and protection of an all-metal cap and the grip of a
Table II. Lens (Dust) Caps.
Size
No.
For Diameters
in.
mm
1.870 47.5 2.244 57.0 2.744 69.7
rubber cap. Because of size standardization, each cap fits the lens with or without the sunshade.
The following tabulation gives lens nomenclature, mount characteristics, and accessory sizes:
1-in. (25.5mm} f/2 (T2.2)
Focuses from infinity to 1 ft
Iris calibrated from//2 to //22 (T2.2 to T22)
Filter size 6 (1$ in.)
Sunshade size 6-7
Gap size 7 1.4-in. (35mm)f/2(T2.2)
Focuses from infinity to 1.5 ft
Iris calibrated from f/2 to f/22 (T2.2 to T22)
Filter size 5 (1 in.)
Sunshade size 5-6
Gap size 6 2-in. (50mm) f/2 (T2.2)
Focuses from infinity to 2.5 ft
Iris calibrated from f/2 to f/22 (T2.2 to T22)
Filter size 6 (H in.)
Sunshade size 6
Gap size 6 3-in. (75mm) f/2 (T2.2)
Focuses from infinity to 5 ft
Iris calibrated from f/2 to f/22 (T2.2 to T22)
Filter size 7 (2 in.)
Sunshade size 7
Cap size 7 4-in. (100mm) f/2 (T2.2)
Focuses from infinity to 4 ft
Iris calibrated from f/2 to f/22 (T2.2 to T22)
Filter size 8 (2% in.)
Sunshade size 8
Cap size 8 6-in. (152mm} j I 3.5 (T3.7)
Focuses from infinity to 10 ft
Iris calibrated from//3.5 to f/22 (T3.7 to T22)
Filter size 8 (2| in.)
Sunshade size 8
Gap size 8 10 in. (254mm) f/4.5 (T4.9)
Focuses from infinity to 25 ft
Iris calibrated from //4.5 to f/22 (T4.9 to T22)
Filter size 8 (2% in.)
Sunshade size 8
Cap size 8
Foote and Miesse: Military-Type Lenses
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