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) |
Miscellaneous
| 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) |
Notes
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.
HOME
