Colour Variation In ND Filters

Hello CML. On a recent job we experienced noticeable colour shifts attributed to which ND filter was in. We were working with all Tiffen filters, but I couldn't say if they were perhaps from different batches, different years. They were sourced from a rental house.

Anyhow, I did this quick test of pointing the camera at a white card indoors with consistent lighting and took an auto white balance with each filter and noted the info. I'll put the results below. I have to say I was surprised. I wonder if anyone is manufacturing a set of ND/IRND filters that is truly colour neutral or at least closer than this? If I can acquire a set that doesn't vary so drastically I would probably do so to avoid this dilemma in the future.

white balance results, Kelvin/tint
No Filter 2800 / -2

N3 2800 / -2

N6 2800 / -3

N9 2700 / -2

IRND 1.2 - 2900 / -4

(1.2 Created by N3 and N9 = 2700 / -3)

IRND 1.5 2800 / -5

(1.5 created by N6 and N9 = 2700 / -3)

IRND 1.8 3000 / -5

IRND 2.1 2900 / -8

Camera was Alexa.

Thanks in advance for replies.

Matthew Schroeder, DP, NYC

The Formatt Pro Stop IR filters should do the trick. I have a set here if you would like to test out. From ND9 to ND2.1

Regards,
Steve Gal
Du-All Camera
(212) 643-1042
www.duallcamera.com

Matthew Schroeder wrote:

class="style4" >> I did this quick test of pointing the camera at a white card indoors with consistent lighting and took an

class="style4" >> auto white balance with each filter and noted the info.

***************

I did a similar test a while ago with our ND’s and Polas with an Alexa. It’s very difficult to find neutral ND’s … it’s VERY difficult to Manufacture neutral ND’s. The only ones that are near perfect are Kodak Wratten ND gels. Last time I looked then were about $75 for a (basically disposable) 3” X 3”.

So one possibility is to have a correction chart made up during the camera prep. With the Alexa it’s easy to create and name WB pre-sets.

Mako/Makofoto, S. Pasadena, CA

Programming in compensating WB presets is what we finally did. So I certainly believe that it's difficult to create a colour neutral ND set, but then again the IFM-1 claims to be neutral like Thorsten said, and I've heard Sony F55's internal NDs don't colour-shift either. (haven't tested to verify) So it is a bit strange I think that 4x5 glass from the known filter companies don't equal those internal options. Anyhow, thank you for the replies.

I have enjoyed the internal ND aspect of the F55 (.9 & 1.8), allowing to work with only a .3 and .6 in the mattebox to achieve any density.

Matthew Schroeder, DP, NYC

Hi,

You can check out the Japanese made TrueND by Mitomo, people are happy with those. They do not come cheap though.
Warning: I am affiliated with them, so I am not as neutral as the glass is. :-

Best,

Herman Verschuur

The variations in ND filters is nothing new for me. It seems like we are just seeing it more pronounced now that we're dropping in 1.2, 1.5 or 1.8 and "bigger" versions to control stop. I had many days of shooting product, models and fashion on 35 while using ND and finding myself in telecine kind of bummed with the shift in green between, say, an N9 and an N6. It was always easy to time it out. I just started to be more precise in my decisions to use a certain ND then I stuck with it for a set-up or scene to ensure that there was uniformity in colour and shift. I've never been a huge fan of Wratten Gels, as Mako suggests using for more uniformity. Maybe for those super finicky shoots it would be a good alternative. But the subtle difference in colour is so easy to combat in post.

Matthew Clark
Director/DP
www.str8films.com
Seattle, WA

We are not affiliated with Mitomo but we do own a set of these.
They are very, very neutral. They are also not cheap, but no IRND filters are.
The downside is that they only go up to 1.5 (at least last time I checked).

Art Adams tested them at our facility and wrote them up.

>Hopefully he will pipe up with a link.

Leigh Blicher
Videofax
San Francisco

Mitomo TrueND and Panchro mirrors seem to be the only truly neutral NDs out there. All others show variations between densities.

I posted some graphs of how two sets of common IRND filters tracked colour wise:

http://www.dvinfo.net/optical-science/one-set-of-nd-filters-to-rule-them-all.html

Art Adams
Director of Photography
San Francisco Bay Area | CA | USA

"Art Adams (CML)" wrote:

>> Panchro mirrors

Dangerous, reflection issues, although actors love to see themselves. Clairmont Camera destroyed theirs years ago. I lent mine to a production/Dp, with strict warnings! Motion control shoot pre HD. I didn't feel guilty when they had to reshoot because of unseen reflections.

Mako/Makofoto, Santa Monica, Ca

>> All others show variations between densities.

Were the Formatt pro-stop filters recommended earlier in this thread also exhibiting variation? Or are these a new offering since your testing?

Thanks,

Theo Stanley
Director / DP / NYC
www.harborpicturecompany.com

Thanks for those tests Art, that article was very helpful.

One thing you wrote almost as an aside was "You can mix hot mirrors with regular NDs, but you can’t mix IRNDs with regular NDs". I haven't noticed it prior, but is there a significant colour consequence of mixing an IRND 1.2 with a (non-IR) ND.3 for example? (compared to a single filter of IRND 1.5). By the looks of it most brands have enough variation between filters as it is that this could be splitting hairs? I've certainly used this type of combination to maintain a stop in changing light, faster to pull the .3 than switch out a 1.5 for a 1.2

From Art's tests the TrueND filters were remarkable. He voiced a hypothetical concern as to if they would steal lustre from skin tones so I wondered if anyone else used them in a production scenario and observed that or the contrary? The other concern was to their longevity since they have use a surface film. Seems valid to weigh that in.

Matthew Schroeder, nyc, DP