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Using two polarising lens filters to block 100% light

Talk Basics - Talk Photography - www.talkphotography.co.uk
It's not entirely camera related but:

As I understand it, if you have two polarising filters stacked on top of each (aligned to the way they polarise) then they will block about 50% of the light. But as you rotate one of the filters it blocks more and more light until it blocks 100% light when it is 90 degrees. This is exactly what happens with two iMax 3D cinema glasses.

I needed to do this using something else so I purchased some cheap polarising camera lens filters from ebay but they do not exhibit the same behaviour. There is a subtle change of light but it does not block anywhere near 100% of the light. In fact, it doesn't seem to block any more light than the first filter. The only change is appearance of the colour of the combined lens which turns from a 50% tinted black to a 50% lightly brownish/black tint.

So my question is, is this normal for camera lenses or are these a problem with these specific ones I've purchased (they were the cheapest ones I could find).

Or put another way, using two "proper" polarising camera lenses aligned 90 degrees to each other, will they block 100% of the light?

TIA

 
Date: Oct 11, 2017   


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