Could not find much about them apart from this
forum post and not so favourable reviews
here.
To quote:
Quote:
Although the concept is intriguing in reality though the results are quite poor and it’s all due to physics. The way these filters are made is by taking a simple variable ND filter, which is a sandwich of 2 types of polarizers and adding a red longpass filter on top of the stack. At this point some of you may already have figured out the issues just from reading the previous sentence. That’s right, all the problems you experience with variable ND filters transfer over and are made worse with the capture of two different light spectrums, visible and infrared.
The dreaded cross pattern is just as bad here, gets progressively worse the stronger IR effect you dial in. Also, because of the qualities of stacked polarizing filters you also induce a lot of softness to the image, washing out fine detail considerably. I guess if these effects is what you are after then great, this is a perfect filter for you but for the general photographer who is seeking the finest image capture possible this filter just isn’t a good idea.
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What do you plan using them for?