Far Red / IR contamination with F3

C

C.A.Magid

Active member
On a recent shoot we ran into what I believe to be Far Red or IR pollution.

We were in a situation where the shooting environment contained a few large windows which were covered with ND.

The resulting F3 footage pushed magenta or red to varying degrees. Not too severe but definitely there.

While it was easy to correct out in this situation, it did bother us that a blue shirt tended purple and flesh tones were not quite right. We also seemed to be battling lighting as our efforts to steer color temperature with correction gels were not producing the results we expected.

If it matters we were using Cooke Panchros, recording to a KiPro mini and were under tungsten balanced lighting (incandescent and kino). At times we had a Tiffen digital diffusion 3 and Schneider black hollywood magic 1/2 in front of the lens.

Wondering if anyone has specific suggestions for the make and model of filters they have used on a F3 to deal with IR or red push with good results?

I am familiar with various hot-mirror, IR cut and other filters from various manufacturers. It is my understanding that each camera behaves differently as far as the wavelengths affected so what works well on a RED may not be the best fit for an F3.

Looking for something I can keep in the matte box nearly all the time to guard against this.

What is the light loss with these types of filters and would they co-operate with F3 built in ND filters when used together?

Any other info would be greatly appreciated.
 
Tiffen T1 and T1/2 are recommended by London Filter Company for cutting far Red pollution on the F3 and Alexa. http://www.thelondonfiltercompany.com/filters.php?filterid=124

From Tiffen fact sheet:
' T 1⁄2 & T1 – Allows camera to capture subtle hues of red, while maintaining crisp blacks and assisting the camera in capturing the wide color gamut it was designed for – removing Far Red and Near Infrared Pollution from 680nm to 720nm – with a 1⁄2 and 2/3 stop loss. (Both filters available in the Far Red Control Kit).'

 
No ND on the camera but ND on the windows.

No real black in the frame to be an indicator. Just blues, browns and white.

Hard to say if the Kinos were a factor. It was a mixed environment with Arri Tungsten, Kinos and even a 1x1 light panel. Quite a bit of ambient was coming via large windows which played in the scene.

Interesting point though.

Kinos are great instruments when it comes to usability (power, weight, heat). However, put me in the camp that has reservations about what their color spectrum does to some skin tones. Never have been blown away with what they do to certain faces. Awfully easy to use and in most cases pleasant to look at. Though sometimes I wonder as there seems to be green/magenta flesh "oddity" when we color correct material shot as such.

Not sure if this was the case here. Been using Kinos for years.

BUT...I am new to the F3, CMOS and true large sensor in general. Whatever was happening is unlike anything I have encountered before.

The F3 was using cinema gamma 2 under both the cinema and standard matrix with detail off and aperture to +10.

THANKS FOR YOUR INPUT AND INFORMATION!


TimurCivan said:
my money is on the Kinos. if you say magenta, that sounds like kino bulbs that are on their last legs. IR contamination turns black things in the frame brown.

look here for extreme examples.
http://reduser.net/forum/showthread...-suffering-from-IR-contamination..HVX-IR-test

Were you Using ND on the camera?
Click to expand...
 
Schneider now also has some great filters available, the Platinums. They work great on the F3, and every other camera.
 
That doesn't sound like IR issues. I've notice some odd red handling in the F3 during testing and every camera has its own color bias.

I was hoping someome would do an F3 color balance on a scope and post the matrix online. I've been using my ex1 matrix, which is probably off a bit.
 
Mitch Gross said:
Schneider now also has some great filters available, the Platinums. They work great on the F3, and every other camera.
Click to expand...

Thanks Mitch.

Your participation here and in other corners of internet is greatly appreciated.

Really like Schneider. High quality stuff. Which flavor of True Cut IR do you recommend? 680 or 750 for F3?

Suppose it depends at what wavelength the camera starts to have issues.
 
Duke M. said:
That doesn't sound like IR issues. I've notice some odd red handling in the F3 during testing and every camera has its own color bias.

I was hoping someome would do an F3 color balance on a scope and post the matrix online. I've been using my ex1 matrix, which is probably off a bit.
Click to expand...

Duke. I know of what your are speaking regarding the F3's natural or basic colorimetry. The F3 certainly has a look and does seem to handle handle the red swatch of the color wheel a little ham fisted. Or I should say there is somewhat of a tint or push to it. At least in the default STD of CINEMA matrix.

But my recent shoot was different. The effect was localized and splotchy for lack of a better description. It was not uniform even over areas of like subject matter. It did seem like the camera was reacting to something like light, shadow, proximity to ND corrected windows, etc. The reverse angles we shot under similar lighting is clear of issues. Anytime the camera was catching any of the ND corrected windows in frame, odd things happened. VERY SUBTLE but odd.

Matrix tweaks are on my to do list. I believe Abel has some alternate scene files with matrix tweaks on their site. But not sure anything which centers the alignment on a typical Chroma DuMonde.
 
This doesn't sound like IR at all though without seeing footage I can't be definite. IR is an issue with certain kinds of black, very dark fabrics or just sometimes an oddball fabric of any color. It is not an issue with flesh or any general lighting so it will show up as a weird fabric in the middle of an otherwise normal looking shot. You have a number of different kinds of sources and that is where I would put my money and I would be willing to bet on bad ND filters on the windows. ND gel is very very prone to being off color and especially to going magenta. I remember being screwed by this in the past . My problem was with Rosco but it was many years ago and as I recall my supplier told me some brands were better than others. Kino Divas also tend to be a little magenta, but regular Kinos tend toward green in my experience.

Its hard to make truly neutral ND gels or even ND and pola glass filters. Many have a color cast. Also quite a few ND glass filters have their own IR weakness that will look like a sensor problem until you notice that you can see red in the blacks to your naked eye. When were testing the EX originally with Tiffen for IR problems I picked up some Tiffen and Schneider ND's (even ND's that were supposed to be IR corrected ) and noticed that they were turning my sweatshirt red and it had nothing to do with the cameras! I advise always looking carefully just with your eyes at any ND filter and look at a variety of black fabrics. Personally I've never seen a neutral Tiffen grad. The only ones I know that are good from my testing are B+W and Heliopan rounds, but I haven't tested all the professional brands that make 4x4 filters.

The F3 is prone to some IR contamination, but it is nowhere as bad as it is on the EX-1 and I think it might escape many people even when it is present. The Tiffen T1 is the only filter I know that will fix it though I've never even heard of a T1/2. That sounds like it might be good also. I would never be without a T1 in my EX-1kit or even my F3 tho I've never used it on an F3 and only rarely on the EX.

Actually its not IR but Far Red (pre IR) that is the problem spectrum. Various camera sensors have their problems in different parts of the spectrum, hence a good filter for the Red might not work on the EX or F3. Art Adams articles on Pro Video Coalition website are a great education on this , tho I think he was way to hard on the F3.

Lenny Levy
 
My Schneider contacts tell me to expect their IRND filters end of calendar year 2011. I've ordered a Tiffen T1. I've been using a Schneider 680 on my EX-1 and it does seem to work in some comparisons I've done (and don't ask me for them because I lost footage). As Lenny says, the issue is really the far red end of the spectrum.

Ned Soltz
 
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