Useful Optomechanical Shop Data

Flange-to-film distances for various cameras

Nikon F series 46.5 mm
Canon R/FL/FD 42.0 mm
Canon EOS 44.0 mm
Leica M 27.95 mm (27.8?)
Leica R 47.0 mm
Leica screw 28.8 mm
M42 (Pentax) 45.46 mm
Minolta AF 44.5 mm
Minolta MD 43.5 mm
Olympus OM 46.0 mm
T2 55.0 mm
C-mount 17.526 mm
CS-mount 12.5 mm

Lens threads

Leica (old? check this) 39 mm x 1 mm pitch (was 55° Whitworth)
EL-Nikkor, Rodenstock, Schneider 39 mm x .977 mm pitch (1/26")
Pentax 42 mm x 1 mm pitch
C-mount 1" x 32 tpi
CS-mount (check this) 1" x 32 tpi (also special 30.5 mm x .5 mm pitch)
Microscope objectives (R.M.S.) .7952"-.7982" x 36 tpi (55° Whitworth)

Eyepiece diameters

Microscopes, low end & early .911"-.915"
Microscopes, modern ?
Gaertner & others .800" (also .764" & .625")
Telescopes .965", 1.25", 2" (cut -.002 to insure fit)

Adapter threads

T-mount M42-.75
2" Telescope ports (useless!) 2"-24UNS (most commercial parts are oversize)
2" Telescope ports (practical) 2.012"-24UNS (sloppy but works)

Filter threads

Nikon (most lenses) 52 mm x .5 mm pitch
EL-Nikkors 40.5 mm x .5 mm pitch
1 1/4" telescope eyepiece 1.125" x 44 tpi (varies)


allowance for aluminum lens cells .001" per inch dia. @ 20° C for -40° C (60° total)
Density of glass 150 lb/ft3 (2.4 g/cm3)
35 mm frame size 24 x 36 mm (.9448 x 1.4173 inches)
35 mm frame diagonal 1.703"
Tripod socket, modern 1/4 x 20 tpi
Tripod socket, large 3/8 x 16 tpi (was 55° Whitworth)
Nikon old style cable release M8-.75 (check this) (camera is male)
Standard cable release M(2.5-3.5)-.5 (camera is female)


Note 1- .75 mm thread pitch is very close to 34 tpi (.747 mm). 34 tpi will work fine in most applications, if suitable change gears are available to cut it (16 & 68 teeth). 50 tpi will work for the .5 mm pitch, if the engagement length is short. There is no good non-metric solution for the 1 mm pitch of any significant length, though 26 tpi may work for some applications. Exact metric threading requires 127 and 100 tooth change gear. Almost exact metric threading can be done using 37 and 47 tooth change gears.

Note 2- The pitch diameter of threads must be measured using special thread mics or with precision thread measuring wires (Van Keuren Corp.). Many commercial parts will have the correct OD, but an incorrect depth thread. If the OD is correct, but the thread had an excessive flat on top, it is likely oversize. Note that the OD is never to exceed the nominal thread diameter. See Machinery's Handbook for specific sizes and formulas.

Note 3- Autocollimation is used to set infinity focus in film cameras. It is extremely difficult to do with CCDs, as the cover glass/IR filter generally returns a bright clear image, whereas the CCD surface returns a dim, difficult-to-evaluate, diffracted image.

Note 4- The 2"-24 telescope port standard is anything but. Most commercial externally threaded parts measure 2" OD, but have shallow threads that equate to a 2.010" size. Internally threaded parts cut to a correct 2"-24 thread either won't fit at all, or risk seizure if forced. If you cut male parts to 2"-24 and female parts to 2.012"-24, they will be compatible with most telescopes and adapters. Take particular care with Takahashi, as their ports are unusually oversize.

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