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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 :)

Red and the infraRED

Deanan said:
This is not a RED specific thing but it does affect some cameras more than others and we do already have a conservative/strong IR cut filter.
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I'm delighted by this... It was one of my fears..

IR can plague Digital Time-lapse (especially daytime work)... Nikons early DSLRs were I think stealing any wavelength to increase sensitivity and suffered horribly with IR..

Years Ago I had a Hotmirror made up in a 4"x4" 3mm... If anyone is interested I will try and dig out the reciept..

Michael Lindsay
 
Any idea where you had that filter made?
 
no time to test it yet, but would a polarizing filter reduce the IR as well ? Might be a workarround if it works.

Manuel
 
First off - awesome thread, mike. My inner (and outer) nerd is having a field day right now.

We noticed something on set in december that, in retrospect, seems very similar to this. As you noted, there was much head scratching.

Deanan said:
I've noticed that the stronger filters (1.2+) seem to be worse than stacking.
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iirc, that's the conclusion we came to as well. I think there was a 1.2 on the camera when we noticed it, and we traded it out for a .9 + .3 But of course, this is completely anecdotal, and probably useless as actual data.
 
Dylan,

yes, BUT they don't seem to make them in Cine sizes, and they don't work well on wider angle lenses. B+W and Schnieder call them a 486 filter.
 
Do reflective ND's have the same problem ? They use a semi-transparent mirror like a pair of cop sunglasses. I think schneider makes them.

Not good for lots of situations because it reflects a nice square of light right into your scene, and you can only use one at a time and it has to be in front of the filter stack.

Matt Uhry
www.mattuhry.com
 
Mike Prevette said:
Dylan,

yes, BUT they don't seem to make them in Cine sizes, and they don't work well on wider angle lenses. B+W and Schnieder call them a 486 filter.
Click to expand...

Tiffen seems to be trying to win back a bit of market share and I bet they would make a 138mm round...here is hoping.

I was pretty freaked out by this post, because the reality of dealing with 320ASA in daylight and having no built in camera processed ND means using filters. I don't want to shoot with a 1/2000 degree shutter!

Dylan Macleod
Cinematographer
Toronto, Canada
www.dylanmacleod.com
 
Matt,

I don't believe the reflective coating on the mirror ND's cuts any of the IR. I could be wrong, but I have a hunch it's not touching the IR.

Dylan,

You should be freaked out, it's a big deal and I don't think people will care till it bites them in the ass. I wasn't scared at first when we discovered the M8's issues, but all it took was one photo with skin and a supposedly black thing to change my mind. The tone of the "black jacket" was so similar to the tone of the Lips, and rudy features of the skin that it was iimpossible to accurately correct out. At least not without making masks for both objects. Even then the skin never looked right.

The filters are a bitch, let me list the reasons:

1) MUST be the outward facing filter. They reflect a ton of light from off axis angles, you don't want that light bouncing into your ND's or other filters.

2) They can't be used on wide lenses without software correction (simple, but an added step)

3) They reflect a lot, which can cause weird pinkish reflections in your scene.

4) They are expensive and not currently made in Cine sizes

5) they are fragile. The Dielectric coating can scratch easily. Remember this is not a piece of gel between two glass layers like ND, it's actually a evaporated metallic deposit on the surface of the glass.
 
Mike Prevette said:
Matt,

I don't believe the reflective coating on the mirror ND's cuts any of the IR. I could be wrong, but I have a hunch it's not touching the IR.
Click to expand...

To quote Pancro: "Our ND filters are good in the near IR and out to about 1200 (nm) in the mid IR."
 
Good to know!

I had only seen spectral graphs for the Schneider mirrored ND, they didn't do anything for IR.

I'm still digging for Pancro's information on this, but I will call them in the morning.
 
Some more IR testing

Some more IR testing

I just did a very little test with the infra red LCD from litepannels, the Hot filter which was removed from my IR converted Nikon D100 and some ND6 just to find out more about this "issue".
In picture -126 you see the IR litepannels shooting straight in the lens.
On -710 you see the hot filter taken from my converted IR Nikon in front of the litepanels which cuts away almost all IR light, and on -891 you see the Nikon filter I used to block the IR. All shot with a Zeiss T2.1/20 under tungsten, not corrected in Redcine. Does anyone know if these hotfilters by Pancro or Tiffen cut the sensitivity or leave a cast like the cyan Nikon filter do ?
 
Schneider Fix

Schneider Fix

I just got off the phone with Bob Zupka from Schneider, who happened to be looking at this very thread when I called. If I remember correctly, he said that he's working on a fix for some of the NDs such as the .9 and 1.2, however he said it will be difficult with the heavier grade NDs such as the 1.5, 1.8, etc.

He explained to me that the 486 has 26 layers, hence the hefty price tag, but he also said that he could easily make a 486 that would fit over the sensor. Because it would be sensor size, it would only cost around $100. The other benefit to that would be that you could leave it on permanently, since it only affects the IR spectrum.

In order for the sensor-sized 486 solution to work, he said the existing filter would need to be removed via some small screws, as is common on other cameras. Unfortunately, I was unable to confirm whether or not the Red's filter is removable (although my Red is sitting on my desk right now, taunting me, I have to wait until I get home to open it!).

He plans on getting his hands on some Reds in the next couple of weeks, and also mentioned plans to contact Red to come up with a solution.
 
Good news that Schneider and I would assume other filter companies are on this as this is a really big problem that will be a deal breaker for many.
 
Mick- A typical hot mirror or 486 does not cut sensitivity or leave any color cast. The exception to the color cast issue is for light entering at steep angles (ie the sides) the filter starts to effect the visible red spectrum thus leaving you with cyan vignetting as I've shown in earlier posts in this thread. I'm a little confused by your test, a filter for an "IR modified nikon" to me means it's passing all IR and no visible light. Am I understanding you right?

DJ- Good news from Schneider. I'm impressed they are watching this. However like Deanan has said the behind the lens filter can only be so effective. At a point your hitting the limits of physics. Thats why he recommends 2 filters, the current behind the lens filter and one in front of the lens. That way you are catching the waves of light at two different points, and filtering as much of the IR wavelength as possible.

I have some small 486 filters I could possible rig behind the lens on a RED, but it would increase the possibility of flare, and obviously would effect the flange focal distance. All in all it's not a great sollution.
 
It's not possible to simply swap out the OLPF/IR cut filter for only an IR filter as they are the same filter. It also has to be done in a clean room by RED. The spec for OLPF/IR is considerably different than the spec for a filter in front of the lens.

We are constantly evaluating new formulations of IR/OLPF filters to see if we can find one that's better than what we have. So far we haven't found one that's better but we will keep trying.

An additional filter in front of the IR/LP will affect FFD but it will also create more inter-reflections and possible degradation depending on the quality of the glass and the AR coatings on the filters.

I've seen 6x6 hot mirrors before but can't find the source at the moment.
 
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