IR - hot mirror & ND configurations...on shoot now.

[C.H.Haskell]

Greetings RED world...

I am on a Boes commercial as DIT/RED tech and getting a lot of questions about the IR filters. Can anyone give me the run down or Dos and Donts when it comes to stacking hot mirrors and ND filters etc? Is there a particular stacking order that will yield the best results? I appreciate any advice, hope all is well. Best.

Haskell

 

[Jay A. Kelley]

Hot mirror furthest away from lens.. Nothing in front of it.
We have a module on this in the RED101 DVD but will most likely not be out in time for you. I will try to upload a private version for you to view.. It may help

Jay

 

[Brian F Kobylarz]

Hot IR

Hot IR

Jay is correct - IR needs to be the outermost filter.

However, if I read your question right, you asked about multiples.
Do not stack multiple IR's!!!

The danger is that the Hot IR reflects back out - so each one added would create a new reflective surface that would be bouncing inside the light path.

 

[Paul Leeming]

One Hot Mirror only, outermost filter tray, mirror side facing out towards actor. More normal NDs as necessary behind along with any other creative filters you want to use.

HTH

Paul

 

[C.H.Haskell]

Thanks fellows, I really appreciate the feedback...I just have clients asking about some strange reddish looking flare in the center of our image...its more obvious on their monitors then it is on my LCD. Almost feels like an IR issue or some kind of flare bouncing around in side the filters maybe? Any idea.

 

[Stefan Scherperel]

Try pulling out the IR filter and see what happens. Had issues on one shot the other day with a hot mirror, ended up having to take it out for one shot, otherwise no problems.

 

[C.H.Haskell]

Hot mirror furthest away from lens.. Nothing in front of it.
We have a module on this in the RED101 DVD but will most likely not be out in time for you. I will try to upload a private version for you to view.. It may help

Jay

Very nice of you Jay, I would greatly appreciate anything I can learn from your experience...not to mention I like sneak peaks. Cheers.

 

[Jeff Kilgroe]

What IR or ND filters are you using? Some can leave color casts on your image. You may have light reflecting within your optical path. This can come from using reflective filters like IR, hot mirror, polarizers, a filter turned the wrong way, etc.. where you shouldn't be using them. Reflections can also come from light leaks. Check for gaps between filter trays. Grab some black wrap and gaff tape and block that light out.

As other's have said, the hot mirror should be the outer-most filter, mirror side facing your subject. Regular NDs behind it if needed. Don't use multiple mirrors and don't stack IR cut filters or IR+ND filters. Don't use a pola unless it's the outer-most filter either. Wait, how does that work with the hot mirror? ...It doesn't. Put the pola back in the bag.

Same with other effects filters for streaks, flares, etc.. You can use diffusion filters inline in some cases like frost / pro-mist. Don't stack glimmer glass filters behind ND filters or with a hot mirror. They have reflective metallic particles... Then again, that could be a desirable effect...

 

[C.H.Haskell]

Thanks Jeff...we have had it in the right spot, outer most facing away from sensor. The exact set up was an ND3 inside and IR/ND9 Pancro on the outer most tray. I am now 90% sure it was this mirror reason. We were able to remove it but its kind unpredictable and I think it has a lot to do with the angle of the lens in reference to the lamps.

 

[C.H.Haskell]

Thought I would share as many useful articles and info I can about IR & RED on this thread while I can.
Here is one.
http://provideocoalition.com/index.php/aadams/story/red_hot_mirror_shoot_out/

 

[Kwan Khan]

Check for gaps between filter trays. Grab some black wrap and gaff tape and block that light out.
.

agreed...

 

[C.H.Haskell]

Yes, I also agree that could have been it. Thank again.

 

[Martin Weiss]

Sometimes it might help to angle the filter slightly - for example if the mattebox has a swing away arm, open that and swing it just ever so slightly - might just be enough to get rid of the internal flare.

 

[Jason Wingrove]

so the issue with stacking hot mirrors is an internal refection one? that your essentially putting a mirror facing a piece of glass? or is there another issue?
jas

 

[Tony Lorentzen]

so the issue with stacking hot mirrors is an internal refection one? that your essentially putting a mirror facing a piece of glass? or is there another issue?

As far as I understand, yes.

 

[Steffen Vala]

I've had those kind of reddish rings/reflections and it was fixed by blocking any light leaks coming from whatever other sources may be leaking light into the lens' path, as others have noted.

Moreover, as DIT/some-form-of-camera-assistant, I always have a neoprene donut to put on the lens when the shot is calling for extra glass in front of the lens itself, especially HM filters. It's great to have this in the bag, because tape and black wrap can get cumbersome (but of course they are also a great solution! Actually I've used a scarf before just when there was nothing better to solve the problem with.)

 

[Marcus Struzina]

polariser behind hot mirror

polariser behind hot mirror

Just a question about using a polariser and a Hot mirror , I've occasionally used a polariser behind a Tiffen hot mirror without apparent weirdness, what should I look out for ? Jeff Kilgore earlier in this a thread mentioned it as a problem.

 

[Jeff Kilgroe]

Polarizers can sometimes act weird or cause some light bounce if they are not the outer-most filter. So this can be a problem if you are also trying to use a hot-mirror or other filter that could also cause reflections or light bounce within the optical path. There are so many different types of filters out there and possible combinations, so the best rule is to test, test and test...