Variable ND filters

[Nils Ruinet]

As the Red won't have built-in ND filters like in other (video) cameras, I was looking for an easy and quick solution to replace this feature for Run'n gun situations, when you have to quickly change filters in the field and don't have an assistant with you.

And then the name "Singh-Ray" came up in another thread : variable ND filters, adjustable from 2 to 8 stops with just one filter. Sounds great...
http://www.singh-ray.com/varind.html

But only available for 77mm and 82mm threads...
If I remember, Red zoom will be 114mm and primes 110mm (this one may change), so they won't fit.

So, do you know if something similar exists for larger lenses like the Red zooms ?
And did anybody already use these kind of filters, would they be good enough to be used with Red ? How do they compare to normal NDs ?

Thanks,
Nils.

[Martin Drew]

I think this is just 2 polorizing filters stacked, that would explain the colour shifts at higher ND settings and why they say you can't use it with polorizing filters. If you want to impliment a variable ND filter in a larger size you could do it by stacking separate polorizing filters to get the same effect. Not quite the same as a standard ND filter though.

M

[Michael Morlan]

The Singh-Ray filter is just two linear polarizers in the same frame. You can create your own in any size by buying two, separate linear polarizers and ganging them together on the lens. Watch out for vignetting on wide angles and take time with a spot meter to mark the filter edges with calibrated f-stops.

Also, watch out for polarizing artifacts in your scene. In the plus side; more intense colors and reduced glare on reflective surfaces (when properly aligned with the glancing light rays.) On the negative side: bands of interference color on polarizing automobile window films.

M

[Blair S. Paulsen]

Michael makes an important point about being aware of auto window polarizing films when using a pola filter. I typically use a circular "true" polarizer which does not require manual alignment which is great except when you have rainbow or color moire issues that are distracting.