By technical editor Matt Allard:
Using cameras that don’t have built-in ND filters can be problematic, to say the least. Variable ND filters are often the solution but they come in varying levels of quality and price. Swapping a Variable ND from lens to lens means using a step-down ring and constantly changing over filters. While there have been some interesting products come to market that has made the process easier, I have never come across a solution that I have found lives up to the level of speed I usually have to operate at.
I recently came across an interesting alternative solution, the Revar Cine Rota-Tray 4×5.65/138mm Variable ND Kit. It is a two filter system designed to fit into a two-stage 4×5.65 Mattebox to create a Variable ND Filter with 1.6 to 8 stops of light loss range. You place the Revar Cine 4×5.65 /138mm Rota-Tray with Circular Polariser in the rear stage of the Mattebox and the Revar Cine 4×5.65 Linear Pol MC in the front stage. Then all you do is rotate the little gears on the top of the Rota-Tray for a variable neutral density effect (Ed – all variable ND filters are a combination of two polarising filters like this).
I used the Revar Cine Variable ND kit on a documentary shoot in Sri Lanka recently and found it greatly sped up the level at which I could operate. By having a universal system that fits into a standard 4×5.65 filter trays in my Bright Tangerine Misfit matte box I was able to control my level on ND precisely no matter what lens choice I used. Variable ND filters are often limited to lenses with a maximum 82mm front diameter, however the Revar Cine System works on any lens no matter what the size.
One of the main concerns I usually have when it comes to Variable ND filters is the loss of sharpness and the color shift that can occur. I was very impressed to see that the Revar Cine had virtually no visible loss in sharpness and if there was a color shift it was so slight that I could not tell. I used lenses from a 12mm prime all the way up to a 200mm lens and was very happy with the results.
The Revar Cine Variable ND kit is a clever new take on the old age problem of dealing with how to control the amount of light hitting your sensor on cameras that don’t feature built-in ND. The only downside is that you have to use a matte box and that often requires rails and some sort of camera rig. With smaller cameras such as the GH4 and a7S users may not want to turn their small camera into a larger rig. For me, the versatility of being able to move the system between multiple cameras and use it with PL lenses such as my Zeiss CP2’s makes it a very valuable piece of kit. For my line of work speed and efficiency is everything. Any piece of equipment that saves me time and lets me spend more time shooting and less time fiddling around with equipment is a good thing.
This from Revar Cine:
The Revar Cine Rota-Tray 4×5.65/138mm with Circular Polarizer is a geared filter tray designed and manufactured in the USA from aircraft grade aluminum and poly materials to interface with the latest 4×5.65 matte boxes on the market today. Commonly referred to as a RotaPola, RotoPola, or Rota-Pola, this geared tray allows for a use of a common 138mmm unmounted circular Polarizer in a rectangular 4×5.65 tray. By insert it into a top loading 4×5.65 size matte box tray slot and spin the gear on either side of the filter tray to rotate the filter inside. This allows for easy rotation of the filter without the need for cumbersome locking and unlocking of a rotating filter stage. The Rota-Tray also allows for rotation of a filter in matte boxes that do not feature a rotating filter stage or if a secondary rotating filter is needed in a non-rotating stage.
The Rota-Tray also has features missing from other competitive products such as standard 0.8 pitch gears on both sides of the filter tray for use from either the operator or dumb side of the camera, a 1/4-20 female threaded hole for mounting of a wireless follow focus for remote crane or jib operation of the filter, and an overall low weight and profile design for maximum convenience.
The Revar Cine Circular Polarizer found in the Rota-Tray is a mid-efficiency Circular Polarizer constructed of Schott B270 glass featuring 38% transmission (1.5 average stop loss) and a special military spec hard Broadband Anti-Reflective Multi Coating (MC) that minimizes reflections and resists scratches from everyday use for optimal image quality. The multi-coating found on this filter is not common in motion picture filters which are generally polished but not coated. Multi-coating greatly increases light transmission for maximum image quality.
For more information head over to the Revar Cine website.