Series filters
From the 1930s through to the late 1970s, filters were also made in a sizing system known as a series mount. The filters themselves were round pieces of glass (or occasionally other materials) with no threads or rings attached. Instead, the filter was placed between two rings; the mount ring either screwed into the lens threads or was slipped over the lens barrel and the retaining ring screws into the mounting ring to hold the filter in place. The series designations are generally written as Roman numerals, I to IX, though there are a few sizes not written that way, such as Series 4.5 and Series 5.5.
| Series number |
filter size |
adapter ring |
| I |
|
|
| II |
|
|
| III |
|
|
| IV |
20.6 mm |
23.5 mm |
| 4.5 |
25.5 mm |
|
| V |
30.2 mm |
33.5 mm |
| 5.5 |
35.9 mm |
|
| VI |
41.3 mm |
44 mm |
| VII |
50.8 mm |
54.346 mm, 36 tpi thread pitch |
| 7.5 |
57.0 mm |
|
| VIII |
63.5 mm |
66.7 mm |
| 8.5/5.5L |
74.8 mm x 5.6 mm |
|
| 8.5/8mm |
74.8 mm x 8 mm |
|
| IX |
82.6 mm |
87.5 mm |
| 93 |
93 mm |
|
| 103 |
103 mm |
|
| 107 |
107 mm |
|
| 119 |
119 mm |
|
| 125 |
125 mm |
|
| 138 |
138 mm |
|
|
