The 100 x 100mm square polariser.
This polariser slots into the filter holder, which is then rotated to achieve the desired effect.
This version is recommended for studio use, or when no filters are required in addition to the polariser.
A polarising filter will increase your exposure by 1Ã¢â€¦â€ stops.
Linear or Circular? (...and we're not talking about the shape)
There are two types of polarising filter: linear and circular.
These terms do not refer to the shape of the filter, but rather the way in which the filter modifies the light waves that pass through it.
The type of filter required depends on the camera. If you use an autofocus SLR (digital or 35mm) in, for example, spot metering mode, you will need a circular polariser. This is because a linear polariser will interfere with the complex metering and AF systems of modern cameras.
If you use a manual focus camera, whether 35mm or medium format, you can use either a circular or a linear polariser. If you are still unsure of the type of polariser you require, check your camera's instruction manual.