View Full Version : Variable ND filters

11-Dec-2011, 15:16

Has anybody used these

they seem to be 2 polas put together

Do they polarise the image or just ND it
I would like to bracket but don't want anything else to change



11-Dec-2011, 15:41
this subject has come up before here. search the forum.

Jim Noel
12-Dec-2011, 09:08
A polarizing filter has two discs, one of which rotates. The rotation can be used to provide variable neutral density. A polarizing effect will be seen most if oriented 90 deg from the sun.

Bob Salomon
12-Dec-2011, 09:32
No, they do not polarize the scene. But if you add another polarizer to it then it will increase the maximum density and also polarize the scene.

For instance, the new Heliopan Variable ND uses the new Heliopan High Transmission polarizing foils. The High Transmission Heliopan polarizer has an optical density of 0.3 (one stop). When made into the Heliopan Variable ND filter it has a density range of 0.3 to 1.8 (one to six stops). If you add the Heliopan High Transmission polarizer to the Vario then the optical density range is increased by one stop overall and the added polarizer will function as a polarizer as it is rotated.

Note: the optical density of 0.3 is a one stop loss of light. The vast majority of polarizing foils are much denser and result in 1 and 2/3rds loss of light. So the High Transmission foil passes 2/3rds of a stop on to the image plane then a traditional polarizer. There is another polarizer that also transmits more light but it is still only transmits 25% more light then the normal polarizing foil which blocks 1 2/3 stops so it is still less efficient then the new High Transmission polarizer from Heliopan.

12-Dec-2011, 13:12
thanks for the useful replys

have just ordered the heliopan