Simple Variable Neutral Density Filter

Step 4 Final Assembly

Screw the two polarising lenses together making sure the normal filter is on the camera side and the flipped lens is on the other side.

If you don't plan on using the unmodified filter as a polarising filter on it's own then you can glue the two together to make sure you don't get confused. If you do want to glue the filters together be careful; to use the filter you have to be able to twist the front filter while the back filter remains stationary - don't jam the twisting mechanism with glue! Also avoid using cyanoacrylate-based glues (eg. superglue and krazy glue), their vapours can fog the glass.

Comments

[yamahito]

Nice. You can also get away without modifying the front polariser if you can get your hands on a linear rather than circular polariser. However these are quite rare these days as they would normally interfere with TTL measurements.

[Zephyris]

If you can get a linear polariser then that is ideal; you will find that the quarter wave plate on the back of the circular polariser will allow the automatic metering etc. to work fine. Linear polarisers are really quite rate these days, the cheapest I could find was around £25 which defeated the low-cost aim!

[A.Mac]

Considering the Singh-Ray variable ND filter runs between $350-$400, I think £25 still counts as pretty low-cost. Regardless, thanks for the 'ible