Infra Red Again

[Dalibor Fencl]

Hi all,
recetly we did a test with RED One for a feature.

The guys that came with the camera placed a large IR filter in mattbox. It was suppose to correct a false violet or magenta dye in picture. When I told them it's strange, I had never heard anything like that, they were a bit mysterious, told me they new nobody ever talked about that issue, but they were confirmed from RED that the IF filter was really needed.

I could hardly believe that.

P.S. There were no NDs. We did it in studio, tungsten light, wide open Zeiss lenses.

 

[Ed Watkins]

I've never used an IR filter with the RED indoors using tungsten.
I use an 80B filter to push the white balance to closer to 5500K to account for the tungsten, but not an IR filter.

I do however use an IR filter outdoors in direct sunlight, as it does correct for RED's sensitivity to IR light (which makes some blacks appear magenta tinted). It's not absolutely necessary, but the color rendition is more accurate with an IR cut filter.

Maybe they are just playing it super safe.

 

[Dalibor Fencl]

Yes, that was what they told me they wanted to address: Blacks tinted with magenta.
OK direct sunlight only.
They said it was hard to correct it.
Thanks.

 

[Birns and Sawyer]

Ed, have you experienced any of the gradient-style problems that were mentioned on an IR filter test here a few months back?

That's the only thing that keeps me a bit hesitant from using IR filters.

 

[Brent J. Craig]

I have seen the IR effect very strongly when using big tungsten lights (Arri T-12s) at close range.

Basically if your light source, whether it's the sun or studio lights, gives off a lot of infrared you will see it in the blacks.

 

[Patrick Tresch]

OK direct sunlight only.

Only when cutting light with (non IR corrected) ND filters (no necessary below ND6, good for DN9/12 and must have for above).

ND filters don't cover the whole spectrum of the red sensor sensitivity (the IR spectrum) so as you increase the ND filtering, you amplify the IR ratio that gets to the sensor, resulting in a color shift.

See you.

Patrick

 

[Patrick Tresch]

I have seen the IR effect very strongly when using big tungsten lights (Arri T-12s) at close range.

Basically if your light source, whether it's the sun or studio lights, gives off a lot of infrared you will see it in the blacks.

Isn't this true only if the visible light spectrum (or wanted spectrum) is weaker than the undesired spectrum (in this case the IR)?

I've shot with thungsten but didn't notice such a huge IR spill. Though they where only small lamps (0.5k and 1k)...

Patrick

 

[Jeff Kilgroe]

IR pollution can come into play, even when the visible spectrum is quite strong. It manifests in various ways, such as pink tint on blacks and shadows or flesh tones. Or it can come in the form of washed out colors in general, strange halos and edge anomalies, possibly other things.

I suppose it's possible to have IR problems indoors, if the lights being used throw enough heat. Mostly it's an outdoor issue and even then, not all outdoor shooting has serious IR issues.

More often than not, an IR filter is unnecessary. But it's good to have a hot mirror and one or two IR+ND filters in the kit.

When the IR shows up as tinted blacks, it's fairly easy to correct out. IMO far easier to correct for that than the color-cast from shooting with tungsten. In an indoor situation with tungsten, I would think and 80C or 80B filter would be far more useful than putting an IR cut filter in front of the lens.

 

[Dalibor Fencl]

Only when cutting light with (non IR corrected) ND filters (no necessary below ND6, good for DN9/12 and must have for above).

ND filters don't cover the whole spectrum of the red sensor sensitivity (the IR spectrum) so as you increase the ND filtering, you amplify the IR ratio that gets to the sensor, resulting in a color shift.

See you.

Patrick

Yes, thanks, I'd red that thread about NDs here some time ago, bit different issue, NDs don't cut IR. Not gonna be our case, we'll be shooting slowmo wide open to 2.8 anyway, but with strong tungsten lamps on green/bluescreen behind.

 

[Patrick Tresch]

2k thungsten bluescreen : are swear words in RED world!



Patrick

 

[Brent J. Craig]

... I would think and 80C or 80B filter would be far more useful than putting an IR cut filter in front of the lens.

The Rosco Trucolor IR's don't require any stop compensation and they are cheaper to buy than an 80C or 80B.

I threw one in my kit just to bring it out and save the day when necessary.

Correcting in post might be OK for drama, but on TV commercials where you have people comparing Pantone swatchbooks, it is a better career move to get it right in camera.

 

[Jason Mitchell]

You may want to audition one even when you're not using ND. I've seen a red light in frame go pure magenta when the camera was balanced to tungsten and using tungsten lighting. Dropping an IR cut in helped bring it back to red. (Changing the color temp of the preview to 5600 also changed it back to red, but changed the color on everything else.) More often than not, I've found an IR cut pretty standard in my kit.

Jason

Jason

 

[Dalibor Fencl]

To IR or not to IR

To IR or not to IR

Well, to throw an IR to a kit seems to be a good option,
sure,
but the question is if it should be in front of the lens all the time long or just wait, check the blacks if there is no magenta in it and if so use the filter.

 

[Brigham Edgar]

2k thungsten bluescreen : are swear words in RED world!



Patrick

mmmmm, yes, i recently found this one out. I heard it was a relatively small issue and in reality it works but aint pretty and causes a lot more work in post. Green screen under tungsten is great, only way to go. It's just a pity there isn't a decent one here in Brisbane that i know of that you can record audio in.

 

[wshultz]

Anyone recommend the best IR filters and merchants for purchase?

 

[Dalibor Fencl]

2k thungsten bluescreen : are swear words in RED world!



Patrick

I know, I know, green is always better, not even in RED world, but what if you need a fresh grass in front of it?
And tungsten is cheaper.

But what about the IR filters. Let's make a poll.

 

[Dan Hudgins]

XB29 filter?

XB29 filter?

I know, I know, green is always better, not even in RED world, but what if you need a fresh grass in front of it?
And tungsten is cheaper.

But what about the IR filters. Let's make a poll.

You might try a XB29 filter to get better color under all kinds of light, it cuts UV, cyan, yellow, and IR, that makes colors more bright, and reduces haze.

It might not work on very wide lenses in front, but the Kinoptic 9.8mm took internal filters, so with some back focus adjustment that might work also...

Here is the link,

http://www.glenspectra.co.uk/SiteResources/Data/Templates/1product.asp?DocID=147&v1ID=

 

[Mitch Gross]

Anyone recommend the best IR filters and merchants for purchase?

Having tested all the available IR filters from the major manufacturers, we found that the new Formatt filters do the best job for the RED One's sensor. We made a special deal with Formatt to supply nicely bundled kits of IR and ND filters at dramatically low prices. These kits will allow you to use various combinations to go from no ND to ND.21 (seven stops cut) with IR protection. Check it out on our website's RED Store.

 

[Dalibor Fencl]

You might try a XB29 filter to get better color under all kinds of light, it cuts UV, cyan, yellow, and IR, that makes colors more bright, and reduces haze.

Isn't it in terms of color something similar to what used to be called Enhancing?
Plus UV and IR cutdown.

 

[Dan Hudgins]

Enhancing vs. XB29 filter

Enhancing vs. XB29 filter

Isn't it in terms of color something similar to what used to be called Enhancing?
Plus UV and IR cutdown.

The normal pink glass Enhansing filter (rare earth elements, i.e. didymium) just cuts yellow light, but is colored glass so works with wide angle lenses.

The XB29 filter "is a patented triple bandpass, interference filter coating that enhances colour and improves overall spectral performance." It cuts 4 bands, but the UV cut seems to come also from the base glass(?). The three bands passed are blue, green and red.

Because the XB29 blocks cyan light (as well as yellow) you get better blue vs. green as well as better green vs. red.

Since it is patented, other companies can not make this kind of filter, "SPECTRAPLUS is protected by U.S. patent #5,646,781".

I did not see any sample images on their web site:

http://www.glenspectra.co.uk/SiteResources/Data/Templates/1product.asp?DocID=147&v1ID=

If they want to sell the filter you would think that they would have some?

It should help cut haze, make the colors more true. You might want to use an 80 series blueish filter with the XB29 to get the best results(?) under warm light. You can use it with a pink glass Enhansing filter to get more yellow cut, like for sodium lights, or florescents.