Series filters are a type of lens filter that were made in several different sizes or series. Many cameras and lenses from the 1930s through the late 1970 use Series filters. Series filters were an early attempt at standardization where a camera user could use one size of filter on similar sized lenses from different manufacturers.

Series filters are round glass or optical resin filters that are usually in a metal mount distinguished by the absence of threads. The filter is mounted by placing it in an adapter. It is held in the adapter either by a threaded retaining ring or by a threaded lens hood that also functions as a retaining ring. The size of the "front" of the adapter is determined by the Series, but the size and style of the "back" of the adapter is chosen to suit a particular lens or camera. Adapters were made in many sizes and in both push-on and threaded configurations. Photographers could obtain an adapter for each lens, permitting one set of filters to be used on more than one camera. "Series to Series" adapters were used to fit larger series-sized filter to lenses of smaller diameter.

The sizes in the series filters are identified by a number or by the diameter of the filter in millimetres (such as series 63 or 93). The number is usually in Roman numerals for integers and in Arabic numerals for half sizes. The series number is often stamped into the mount on their circumference. The progression of the integer sizes is in imperial .

The diameter of the filter for each series is:

Series Diameter (") Diameter (mm)
IV 13/16 20.6
4.5 ~ 25.5
V 1 3/16 30.2
5.5 ~ 39.5
VI 1 5/8 41.3
VII 2 50.8
7.5 ~ 57.0
VIII 2 1/2 63.5
IX 3 1/4 82.6
X 4 1/2 114


  • Warren, Bruce, 2001, Photography, Thomson Delmar Learning, ISBN 0766817776.