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Variable ND

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Todd Terry
Variable ND
on Oct 30, 2012 at 11:09:32 pm

Any of you guys use "variable ND filters"? (i.e., using polarizers as ND)

We've been using the Canon C300 for about a month or so, and while I LOVE almost everything about this camera, it's soooo light sensitive that it can be problematic at times.

For interiors, it's a godsend... you could literally light a scene in a pitch black room with three birthday candles (and no gain noise at all). For for exteriors, that's another story.

I like to shoot with my lenses fairly open. Most of my primes are either f1.2 or 1.3 and I'll often like them ALL the way open... but that can be a struggle. Earlier today I was on an exterior shoot in hazy/bright sunlight... I had the camera's internal ND filters clicked up as high as they will go (6 stops), I had the ISO turned down as low as it would go (ISO 320), AND I had an ND filter (.9) in the matte box, and I STILL had to stop the lens down way more that I would have liked (.9 is the highest 4x4 filter I have, and I didn't want to start stacking filters in the box). Since I was shooting 24p my shutter speed was 1/48th, and obviously I don't want to go higher than that.

I've never really used polarizers as variable ND filters, and frankly I'm not even sure you can (or should) do that with 4x4s (mine are cine lenses so while all the barrels are the same size, they do not have threaded fronts... so I need to use the matte box).

If anyone has any bright ideas as to how to make this eaiser, I'm all ears...

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Mark Suszko
Re: Variable ND
on Oct 31, 2012 at 2:44:33 pm

I thought stacking all the filters was what the matte box is for?

You can't always use this because of the motion artifacts it can induce, but you can add more shutter to simulate adding ND sometimes.

Do you have the option to de-tune the sensor, apply negative gain, as it were, outside? Our Pannies have this ability but I don't know that DSLR's do.


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Todd Terry
Re: Variable ND
on Oct 31, 2012 at 2:58:15 pm

[Mark Suszko] "I thought stacking all the filters was what the matte box is for?"

Well, yeah, but you generally want to keep them at a minimum. Every one you add to the sandwich is just another surface for light to bounce back and forth between. I try to keep it to one, rarely to two. Never more.


[Mark Suszko] "you can add more shutter to simulate adding ND sometimes."

Yeah but that really screws with your motion blur. I try to stick with the "one over twice the frame rate" rule for shutter speeds. You don't have to crank shutter speed up much at all before you start getting that "narrow shutter" look... then suddenly you're shooting "Saving Private Ryan," or "Gladiator."


[Mark Suszko] "Do you have the option to de-tune the sensor...I don't know that DSLR's do."

Well the C300 is not a DSLR... but no, I don't think so. The ISO range is from 320 to 20,000, with ISO 850 considered "optimal" for that camera, for both noise and color grading (I think on the C300 that ISO 850 is considered "zero" if you are thinking about it as if it were gain, not ISO). For exteriors I crank it all the way down to 320, which is as low as it will go.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Angelo Lorenzo
Re: Variable ND
on Nov 3, 2012 at 1:56:21 am

I personally don't like using variable ND filters. Even the best on the market have issues with shifting color casts as you adjust the filtration; shifting from cool to warm.

If you do some test footage and find that you're ok with the level of color shift then I say all's fair. It's a good chance to lighten the load of your kit.

Angelo Lorenzo
Fallen Empire Digital Production Services - Los Angeles
RED transcoding, on-set DIT, and RED Epic rental services
Fallen Empire - The Blog
A blog dedicated to filmmaking, the RED workflow, and DIT tips and tricks


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