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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Some questions about IR contamination

M

Mike N

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Hello,

I want to know if the IR contamination problem only appears when shooting outdoors with the NDs and at what ND density it starts to show up (.06 , .09 ?) , or is it visible in interior/studio shoots in tungsten or daylight lamps.

I'm asking this because I want to purcahse a IR filter (I read that Formatt's Hot Mirror is the best next to the Pancros but those might bring unwanted glare and flares in the image) and if this happens also in the inside i'll only buy the clear filter without NDs in it. If it doesn't I might as well get it with .09 ND in it so that I won't use 1 or 2 ND's separately in the mattebox.

Does my logic make sense ?

Thanks,
Mike
 
Mike N said:
Hello,

I want to know if the IR contamination problem only appears when shooting outdoors with the NDs and at what ND density it starts to show up (.06 , .09 ?) , or is it visible in interior/studio shoots in tungsten or daylight lamps.

I'm asking this because I want to purcahse a IR filter (I read that Formatt's Hot Mirror is the best next to the Pancros but those might bring unwanted glare and flares in the image) and if this happens also in the inside i'll only buy the clear filter without NDs in it. If it doesn't I might as well get it with .09 ND in it so that I won't use 1 or 2 ND's separately in the mattebox.

Does my logic make sense ?

Thanks,
Mike
Click to expand...

That's right IR contamination is generally only going to happen with an absorptive ND filter .9 or greater. That's because the ND is passing IR light while blocking visible light. Thus when you open up to compensate for the optical light blocked by the ND you are overexposing the sensor with IR light, overcoming the standard IR filter in front of the sensor.

IBloom
 
IR is heat. Any excessive heat will generate extra IR. So in theory you could pile up tons of tungsten lights indoors and then put on ND filters until IR contamination appeared. In practice, no sane person lights this way (it is how we test for IR protection though). So the only place we usually see the excess heat is on warm days outside.

The camera's sensor has a standard IR reflector (aka Hot Mirror) on it. But on a bright day one will typically pile on a lot of ND filtration in front of the lens. The problem is that standard ND filters block the visible spectrum but not IR. So the effect is to transmit a great deal of IR relative to the visible light, making the IR pollution quite evident. The fix for this is to use a IR reflector (Hot Mirror) in a filter to place in front of the camera lens. Remember, it should always be the first filter in the mattebox so that the IR is reflected out into the world instead of onto the back of another filter.

Most REDusers have typically reported only noticing IR pollution with ND9 and above, but this is completely dependent on the environmental factors of the day and location. It is technically possible to see IR pollution with no ND (a REALLY hot day) or no IR pollution with a great deal of ND (a cold day). One DP called me quite confused when she could not repeat the results of an IR test she had conducted months earlier. We eventually realized that it was because the first test was in July and the second in November, both in New York.

Abel sells several IR filters from the different manufacturers and we currently prefer the Formatts for the RED One. What is unique about the Panchros is that they are true mirrors, reflecting ALL light including the IR wavelengths. But this can be a big issue with light reflecting back into the scene.
 
Thanks Mitch and Ian. I was very excited about Pancros at first but then I heard about the problems with reflections and flares and calmed down :) .

@Bassam : Using a IR filter usually solves this problem but some filters do bring a certain colored tint in the image (the color differs from filter to filter) . The least amount of tint is achieved with the Formatt hot mirror filter and with the Pancros which have none but you need .09 and above to filter all the IR light out and as i've said, you might have flares glares and other nice things in the image.
 
Having owned (and sold) two sets of Pancros, I can tell you that they probably work great with cine lenses, but they are a total disaster with Nikon still lenses. We had ghosts in the machine in just about every shot, and it made no difference what we did. . .there they were. Exactly why Nikon lenses ghost so horribly (when, apparently, cine lenses do not) I have no idea.

We have not experienced ANY ghosting issues since changing to the Formatt IR+ND filters.

An alternative solution is to purchase a "hot mirror." This means stacking filters (which can lead to issues on occasion), but it is a lot less expensive.

Stephen
 
Wide angles

Wide angles

Mike N said:
(I read that Formatt's Hot Mirror is the best next to the Pancros but those might bring unwanted glare and flares in the image)
Click to expand...

Silvered ND filters may work better if you need to use wide angle lenses, like wider than 35mm at 4K since Hot Mirrors can leak IR in the corners of the frame. To avoid reflections cut some black Neoprene sheet with a hole large enough to shoot through and push the lens up to the back of the filter, put the silver size on the actor side. Also if the lens has white lettering around the front you should paint that black or put dull black tape over that since anything that can reflect back onto the silvered surface can make reflections. The SLR lenses may have a larger front element to make larger reflections on, so you see more reflections from them than cine lenses because the cine lenses have smaller elements because the cover a smaller image circle, and cine lenses may have better coating and blackened edges to their elements...

Another way to cut reflections is to use a dye ND filter between the silvered filter and the lens, maybe a 0.3ND dye filter plus a 0.6ND silvered filter, the reflections need to pass twice through the dye filter and so are cut two stops by the 0.3ND. Try to put the back of the silvered filter in contact with the dye ND filter or spaced with a thin black paper gasket, since if the filters are at angles from the play in the holders you can get the reflections going like a "hall of mirrors" effect.

When using wide angle lenses interference filters aka Hot mirror are maybe not as good as filters that absorb IR light, e.g. heat absorbing glass.

The heat part of the spectrum is only part of the problem, the sensor's bayer filter can pass near red IR which is not so much heat as dark red light, that can expose the blue sensors and shift red subjects to pink, so what you need to cut are deep red and near IR rather than so much far IR and what we feel as Heat, so the near IR and far red will be there even on overcast days for the most part.

If there is not much motion in the shot it may be better to stop down the shutter angle, if you go from 180 to 90 you can use a 0.6ND rather than a 0.9ND, or if you go from 180 to 45 you can use a 0.6ND rather than a 1.2ND etc. That way with wide angles you avoid the problelms HOT mirrors have with wide angle lenses, and maybe some reflection issues...
 
Stephen Pruitt said:
Having owned (and sold) two sets of Pancros, I can tell you that they probably work great with cine lenses, but they are a total disaster with Nikon still lenses. We had ghosts in the machine in just about every shot, and it made no difference what we did. . .there they were. Exactly why Nikon lenses ghost so horribly (when, apparently, cine lenses do not) I have no idea.

We have not experienced ANY ghosting issues since changing to the Formatt IR+ND filters.

An alternative solution is to purchase a "hot mirror." This means stacking filters (which can lead to issues on occasion), but it is a lot less expensive.

Stephen
Click to expand...


We have Panchro hot mirror NDs at .9, 1.2 and 1.5 and they work great on the RED. We back them with standard Schneider NDs as needed to get the stop. Agree that IRs are not needed below .9.

Oh, and those are on Zeiss UPs in an Arri MB-20 II MB.

M
 
Hi Mitch, I have been trying to buy an IR cut off filter and a 1/2 CTB filter from you or filmtools.com for about 2 months, no success yet, and there is nothing wrong with my credit cards...

(filmtools.com has some issues with Norweigan credit cards that apparently no one else has, Abelcine seems to have too much business to bother about such a small order - sorry to say in a public forum, but I have tried time and time and time again... hopefully this time I will be able to complete my order)
 
Eirik Tyrihjel said:
(filmtools.com has some issues with Norweigan credit cards that apparently no one else has)
Click to expand...

They have the same problem with Aussie CCs - the banks here won't divulge addresses on request so their "verification" procedures don't work. If you can ever get in touch with Filmtools' billing people you can wire money.
 
@Eirik - if you are not from the US only wire transfer will work. Give them an e-mail here : Martha [martha@filmtools.com] and they'll surely help you out.
 
We're very much aware of this situation and are woring to create an answer. International internet credit fraud is a huge problem and we've been burned before. In the meantime, if anyone is having a problem placing an order please contact me directly and I will shepherd your request to a person who can deal with you directly.
 
I Bloom said:
That's right IR contamination is generally only going to happen with an absorptive ND filter .9 or greater...
Click to expand...

I disagree. I have seen several occurrences now in studio situations with no ND where an IR filter was necessary to get proper color rendition. As long as you have light sources rich in IR (such as tungsten lamps) there will be certain fabrics, materials and inks that bounce back lots or IR.

This has happened a couple of times with color corrects on commercial shoots. Some of the inks they use reflect IR.
 
Brent J. Craig said:
I disagree. I have seen several occurrences now in studio situations with no ND where an IR filter was necessary to get proper color rendition. As long as you have light sources rich in IR (such as tungsten lamps) there will be certain fabrics, materials and inks that bounce back lots or IR.

This has happened a couple of times with color corrects on commercial shoots. Some of the inks they use reflect IR.
Click to expand...

Ditto that, exactly my experience and I was happy as a dog finding that we had IR+ND's in the box though not ordered.
Was a set with about 90kW's of Tungsten and a RED painted background apparently reflecting lot of IR.
 
NIce class gentlemen...:beer:
 
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