How to check the quality of the optical polarizing photo filter?

This method can also be applied to other polarizers.

We place our filter in polarized light and rotate it. As a polarized light source, we can use an LCD computer monitor or a laptop screen, it is best if our ‘background’ is bright (white).

There will be 2 characteristic filter positions:

1. The filter is as transparent as possible
2. The filter is all black

In the first case, the filter polarity plane coincides with the plane of the polarized light emitted by the screen.

In the case of the second, these planes cross and the filter does not let any light through. A well-functioning filter should be completely black at this point. This is a distinctive feature good polarizer.