A long-long time ago I've read Prof. Lorenzo Vanini's article about direct composite restorations. In his article, there were some really interesting photographs where one could see all the details in the teeth. As I was so excited about this technique, I've started to do some search on the internet and on a nature photography site I found some clues about how to do it. Photographers using a cross-polarizing technique to photograph amphibians as they can see the skin much better if there is no reflection.
So I made my first cross polarising filter setup with films and glass polarising filters. It worked beautifully, but soon I realised the setup is really time-consuming if my flashes are on a bracket and the flash heads are not locked in a parallel position.
So after some time, I've designed my PolarFrame to avoid the time-consuming process.
Now it just seconds to attach the PolarFrame to the lens and take stunning cross-polarised photographs with twin flash setups.
The filter size of your lens