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class="style16"> Red IR

Published : 13th September 2009


Hi there,


Question :


We shoot 120 frames with the Red, but 25 Frames as well. So the level needs to be high enough for the 120 frames, and we need to stop down for the 25 frames. So there´ll be ND Filters involved. That for we need IR Filters best combined with ND.


Since we use the Optimo and the 10mm Ultra Prime we need to use 6.6x6.6 Filter size.


Are those available? Are there any other options, except switching off the lights?


Best regards
Kai Lachmann, AC
Berlin



Schneider has a 6x6 Tru-Cut which I use but I believe Tiffen has a 6x6 Hot Mirror.  I don't use a IR unless I have ND6 (2 stops) or more in the Mattebox.


Good luck,


Dane Brehm
310.710.2658
DIT : Data Tech
Phantom | Red | S.Two



Both Tiffen and Schneider and Formatt make IR filters; Tiffen and Formatt also make ND IRs (that is, NDs with a fixed IR value built in) in both 4x5 and 6x6


Hope this helps


Byron Shah
DP Los Angeles



Abel sells Formatt IR filters in 6x6. We really like these for the RED. You don't need IR if you stop down, only if you use ND.


Mitch Gross
Applications Specialist
Abel Cine Tech



Take a look here:


http://provideocoalition.com/index.php/aadams/story/ir_cheat_sheet/


Art Adams | Director of Photography
San Jose, CA USA
www.artadams.net
art.provideocoalition.com
415.760.5167



>>MPTV Filters Manufactured to stop IR pollution.
>>Hot Mirror: Tiffen - Formatt - Rosco
>>IR TRUE CUT 750 - Schneider
>>IRND (Manufactured by Tiffen) for USE with Sony F35 and Panavision Genesis.


Does anyone manufacture an IR filter *without* built-in ND that works to solve the problem I see all the time where, for instance, I'm shooting a Mariachi band against green screen, and the four people have "black" outfits on (by eye), and each one is a different color as seen by, say, an F23 with a Digiprime running almost wide open?


Bob Kertesz
BlueScreen LLC
Hollywood, California



Bob Kertesz wrote :


>>Does anyone manufacture an IR filter *without* built-in ND"


And by extension, why after spending $$$$$$$ on R&D then manufacturing and marketing a camera body for 6 figures can't a company like Sony put the right level of IR cut directly onto the sensor?


Or RED for that matter. The idea of a having to spend $$$ on a 4" glass filter must be especially galling at the more budget end of the owner/operator market

.
I spoke recently to a rental house who were quite peeved at the realisation that they were now going to have to invest in thousands of pounds worth of filters to accompany their fleet of (already very expensive thank you very much) F35s.


Tom Townend,
Cinematographer/London.



>>> Does anyone manufacture an IR filter *without* built-in ND


Sony has always used a longer wavelength IR cutoff point in their OLPF than some other manufacturers and thus is somewhat more compromised by this issue.


The Formatt folks were very accommodating and made me up a set of five IR Filters a while back. (I also am a strong proponent of their HD Soft filters, but that is another story.) I told them where I wanted the cutoff point and they took it from there. They weren't cheap, but the production company paid for them <grin>. Worked like a champ. Note that you will typically lose about 10 percent in the red channel (depending on where you specify the cutoff point) and have to compensate with a corresponding amount of increased red gain.


Tom Tcimpidis
L.A. DIT/VC/Tech Maven



MPTV Filters Manufactured to stop IR pollution.
Hot Mirror: Tiffen ? Formatt ? Rosco
IR TRUE CUT 750 ? Schneider
Pancro also makes IRND filters. they have no color shifts


Sergei Franklin
www.sergeifranklin.com



Bob Kertesz wrote:


>> "Does anyone manufacture an IR filter *without* built-in ND"


Yes, I have seen such filters by Formatt and Rosco, and Schneider.


Tom Townend wrote:


>> why <SNIP> can't a company like Sony put the right level of IR cut directly onto the sensor? Or RED for that >>matter.


These cameras do have adequate IR filtration for a normal spectrum of light. It's just when you use a ton of ND, you are greatly reducing the visible light, without altering the IR, so that the proportion of IR gets many times greater than the norm. You are effectively creating an IR pass. The same would happen with film stock, it's just not been common to use 5 or more stops of ND with film; at that point you'd normally switch to a slower stock!


Jendra Jarnagin, DP, NYC
www.floatingcamera.com



So,


Is my Schneider REFL ND's considered a HOT MIRROR filter and thus capable of cutting IR contamination?


Cheers,


Jeff Barklage, s.o.c.
www.barklage.com
agent: TDN ARTISTS www.tdnartists.com
USA based DP



>> Does anyone manufacture an IR filter *without* built-in ND... that works to solve the problem... the four >>people have "black" outfits on (by eye), and each one is a different color as seen...


Yes, while I have tested this with Phantom, I have not tested it yet with f23... different rgb filters but same idea.... so maybe different cut, but same idea... more to follow when I wake up


Mark H. Weingartner
LA-based VFX DP/Supervisor
http://schneiderentertainment.com/dirphoto.htm



Yes Jeff, the reflective ND's cut all the wavelengths out past the camera's sensitivity equally. No ratio shift in near IR to visible light as you increase ND values. But do be careful of reflections.


Bob Zupka
Product Manager
Schneider Optics



I believe all of the manufacturers make their various IR filters available with or without ND combined. Please note that every sensor type is a little different and therefore may benefit from one manufacturer's design over another's.


And BTW, all the Phantom HDs now have a built in IR absorber sandwiched into their OLPF. An absorber is preferable to a reflector in that it, well, doesn't reflect anything so there is no danger of flaring or other issues. It eats a bit of exposure but it actually helps make the colors on the Phantom quite true, and has the added benefit of shifting the camera's native color balance somewhere in the middle between tungsten and daylight. So the camera is equally sensitive to both with no additional noise.


So no additional IR filtering needed for Phantom HD, ever. At the time of Mark's test with an IR filter on the Phantom, the IR absorber was not yet implemented on the OLPF. It now is.


Still waiting for a Certain Colored Camera Company to try implementing a similar upgrade to their OLPF. Perhaps on one of those soon-to-arrive models...


Mitch Gross
Applications Specialist
Abel Cine Tech



>>And BTW, all the Phantom HDs now have a built in IR absorber sandwiched into their OLPF.


How does an IR absorber work? What material is used?

Art Adams | Director of Photography
San Jose, CA USA



Mitch Gross wrote:


>> And BTW, all the Phantom HDs now have a built in IR absorber sandwiched into their OLPF.


Depending on where you are and where you are renting your Phantom and where they are renting it from, I would very specifically ask about this... my own telephonic research suggests that not very owner of a Phantom has sent his or her camera back for retro-fitting... I would love to be proved wrong on this.


Mark H. Weingartner
LA-based VFX DP/Supervisor



>>How does an IR absorber work? What material is used?


The IR absorber is colored optical glass (which absorbs certain wavelengths irrespective of the angle of incidence of the light). The other alternative is to use an dielectric filter, which has much sharper transitions and better peak transmission. It has two drawbacks : one is that it's transmission is angle-dependant (so you may get a leak with angled light, even if you didn't have one with normal incidence); and the second is that it bounces the IR back towards the lens - in IR, the filter is essentially a perfect mirror. and that reflected IR can bounce back and forth and ultimately end up at an angle that will make it pass through the filter. (this sounds worse than it is in practice - the overall effect, while quite visible, is small). We have a dielectric filter on the sensor coverglass, and a color glass filter in the low pass stack.


Please note that on phantoms, the low pass stack can be removed/changed by the user.


Radu Corlan



>>the other alternative is to use an dielectric filter, which has much sharper transitions and better peak >>transmission.


As I had no idea what a dielectric filter is, I took a look on Wikipedia. Apparently it is also known as a dielectric mirror, and is similar to a dichroic filter.


Here's the dielectric mirror page : http://en.wikipedia.org/wiki/Dielectric_mirror


And the dichroic filter page: http://en.wikipedia.org/wiki/Dichroic_filter


>>we have a dielectric filter on the sensor coverglass, and a color glass filter in the low pass stack.


The colored glass filter sounds a bit like what Tiffen does in their ND IR filters: a dye filter that absorbs whatever spectrum doesn't get blocked by the dielectric mirror.


Art Adams | Director of Photography
San Jose, CA USA



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