Variable NDs are usually thought of as a necessary evil for DSLR shooters, useful because they allow rapid exposure control, but also associated with colour shifts and images where the subjects have less than lifelike skin. They’re also seen as a cost effective solution to a problem that was traditionally solved with matte boxes and expensive sets of fixed strength ND filters.
Now that’s all to the good for most of us shooters who might be on a deadline and just want to get the job done. But for productions where you’ve got cameras and lenses that might be costing north of $100k US, the notion of strapping a variable ND filter to the front of your rig might get you a few funny looks. Not to mention that, if your camera already has built-in ND filters, then surely there is no need for a variable ND?
Tiffen, however, think otherwise, and have developed a vari-ND system that’s suitable for use on high-end productions. Even with the best kit available, shooting outside in strong light can make setting your exposure very challenging – especially as base ISOs for Log-style shooting often start at around 800. Your camera’s built-in ND filters may get you close, but if you want to shoot at the widest apertures on a very bright day then you’ll still need help.
We saw the Multi Rota tray kit at IBC this year but this is the first time we’ve been able to use it ourselves, courtesy of Tiffen – and it’s very impressive.
The kit comprises a 4 x 5.65 size Multi Rota filter tray that fits in a single stage of a compatible matte box. The tray has room for two special, very thin, panes of glass. The first pane is a polariser that rotates; and when combined with the second polarising filter offers from two to six stops of light reduction. Other manufacturers have had similar two filter neutral density solutions for some time, but the difference with the Tiffen solution is its slimness. This means that is a regular two stage matte box you can easily combine variable ND with another stage of filtration: a diffuser for example. It’s also possible to attach a motor to the Rota Pola to allow remote adjustment of the ND using the same type of controllers you might otherwise attach to focus or iris gears. This could be useful for changing exposure on Steadicam shots which move between interiors and exteriors, where you would otherwise have to remotely pull iris and alter the depth of focus.
The nature of the two filters working together will still produce a polarising effect: so water, computer screens and car windows won’t look quite right; however if you’re shooting outside with very fancy kit in light you can’t entirely control, this would be a great option.
Another use for the filter is as a variable warming effects filter. This is done by reversing the rotating polarising filter tray. Instructions for this are marked on the filter tray itself.
The unit has been designed to be compatible with industry standard mounts and various matteboxes – there’s a compatibility list on Tiffen’s website here.
Could be an expense for the production to pick up though, as the units start at around £850 GBP for the Variable ND version.