IR nd filters .... A few questions

Albion Hockney · May 8, 2015

1. With tiffen filters what is the difference between the ir nd filters and the hot mirror ir nd filters?

2. With tiffen filters how do you use the non nd stand alone hot mirror filter. Is it effective to get standard nd filters and just place the hot mirror infront of them ? What strengths of ir nd work best with the hot mirror or does it work in such a way that it doesn't matter?

3. Does anyone use Schneider platinums with the red mx sensor and what do they think? I have seen tests and the footage that comes back looks super green I feel it must be losing Atleast some color information no?

Is there an overall preference between

Schneider platinums, tiffen hot mirror nds, and tiffen standard ir nds?

Thanks for any insight, I know there are a lot of topics about these filters and no clear answers it seems.

Albion Hockney · May 8, 2015

And can you stack IR ND's or are you only supposed to use one IR ND and then standard NDs under that?

Satsuki Murashige · May 8, 2015

Generally, IR filters are made to either absorb excess magenta by adding green, or reflect the IR away with a mirror coating. Hot Mirrors are the latter type and most straight IRs are the former. Hot Mirror IRs are a combo filter. There are also dichroic IR filters like the old Schneider IR750 and Rosco TruColor that cut off specific wavelengths of light close to the IR end of the spectrum. These are not combined with any NDs, they are just pure IR filters. Nobody really uses them anymore since sensors and filters are more advanced now. They can have an off-axis problem where with wide lenses, the image at the edges would get more or less correction than the middle because of the light coming it at extreme angles to the filter. The Schneider IR690 was infamous for this.

Which to use depends on the specific sensor design. Red MX sensors pretty much only work with Hot Mirrors. I think things have changed with the new Skin Tone OLPF for Dragon. Arri and Sony require IRNDs but if you are using the internal NDs on the cameras which already have IR built in, then you can probably get away with straight NDs up to about N6.

Finally, there are two new brands of ND filters which seem to eliminate the need for IR or Hot Mirrors. Mitomo True NDs and Formatt Firecrest NDs are very neutral straight ND sets which (from what I understand) use metal particles imbedded in the glass to reflect or absorb the IR instead of using a special coating. I have not seen the Firecrest yet, but the Mitomos work very well on Sony, Arri, and Red without a color shift. Presumably they work great on film as well, Greg Irwin could tell you for sure. So everyone is switching over to those now. They are twice as expensive though.

Satsuki Murashige · May 8, 2015

With IRNDs, you should stack them since there is incrementally more green in each filter as you step up to compensate for the increase in IR. But since each camera responds to IR differently, it won't be consistent enough to keep your footage from being more or less green, shot to shot. Internal NDs specific to a particular camera should do better.

You can't stack Hot Mirrors because their reflecting qualities would cause multiple reflections. With a filter pack, you should always place the Hot Mirror in the furthest tray away from the lens for this reason. One of the big downsides of Hot Mirrors.

Albion Hockney · May 9, 2015

thanks much. the Firecrests look great from the reviews and very affordable. True ND's seem like the ones to really use but yes expensive.

look forward to the day all cameras have internal ND or a better way of dealing with this!

Albion Hockney · May 27, 2015

Hey Satuski I have a production about to start and the rental house only has Tiffen IRND's and they are pushing it on me. I'm curious what your experience was that resulted in you saying that "IRND's pretty much dont work with the red mx"

thanks much!

Satsuki Murashige · May 27, 2015

The Tiffen IRNDs don't remove far-red on the Epic/Scarlet MX sensors. Only Hot Mirrors really do the job. So with the IRNDs, you're just adding green overall to compensate. You can sort of get away with it up to about ND1.5 if you add a Schneider IR750 IR Cut filter in front, or a plain hot mirror (not ND). But it's not ideal, you'll get increasingly reddish blacks and greenish midtones above N9 with the former and deal with an extra filter with the latter. How good of a relationship do you have with this rental house? Can't they just sub a set of Hot Mirror NDs for you? Kinda short-sighted of them to not keep a potential new client happy if you ask me.

This is a non-issue on the Dragon sensor since the new Skin Tone OLPF (have not tested Low Light) does such a good job of filtering out IR on it's own. We used IRNDs on a Skin Tone OLPF Dragon this week on a commercial and it was a little green but otherwise fine. Obviously, TrueNDs or Firecrests would have been ideal but they are not too many sets up in SF yet. We were shooting wide open on Summicrons day and night.

Albion Hockney · May 28, 2015

thanks much for the information, it's a new relationship and the situation is a little weird because of how the production has gone about things. Hopefully should work out today. Nothing worse then a rental house that won't just admit they don't have the right stuff they told the producer "Yea we have the best filters, nothing better then Tiffens" haha.

I'm in a 2 stage box and shooting 1/8 pro mist so I can't toss anything else in there and would really like to not anyways even if I had the space. Hopefully can get them to sub rent some hot mirrors.

yea wide open in the day is tough! I had ND 2.1 on the last thing. luckily we had hot mirrors. I bet those lecia's were looking good though