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Hot Mirror & IR filters

hot mirror ir filter filters infrared
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#1
QuickHitRecord

Posted 12 November 2012 - 01:53 PM

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I am trying to better understand the difference between of these filters. I have come across several resources:

From Tiffen:

Unlike many photographic films, the CCD or CMOS of a digital camera is inherently susceptible to infrared contamination, even when the manufacturer attempts to reduce this problem by adding an infrared absorbing filter on top of the image sensor. Because these filters do not have a sharp cutoff at the infrared wavelengths there has to be a compromise in order not to exclude visible red wavelengths. This results in some infrared wavelengths being allowed to pass. While minor infrared contamination does not normally cause much of a problem for visible images, when using conventional neutral density filters especially denser grades, this issue is multiplied by the filter factor


From Cavision:

The Hot Mirror filter reduces the amount of infra-red light entering the lens while having no affect on the wavelengths of light in the visible spectrum. Digital sensors are especially sensitive to IR light, which can cause aberrations and colour shifting in the image. The hot mirror filter is especially useful when using a neutral density filter because the ND filter will increase the ratio of IR light to visible light. The Hot Mirror ND filter accomplishes both tasks in one combination filter, freeing up an extra filer stage in your matte box.


Is there anyone using IR or hot mirror filters that can clarify? How significantly do these filters improve your image?


#2
andy lee

Posted 12 November 2012 - 04:23 PM

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quote from Roger Deakins cinematograper on James Bond Skyfall from his forum
http://www.rogerdeak....php?f=2&t=1685

"I am using no specialized IR filters. I do use NDs when shooting exteriors. I generally shoot with a 400 ASA setting and a ND6. I have seen no adverse colour shift and almost everything I shoot is coming in where I want it with our chosen LUT.
The IR issue is not something I have experience of at all with this camera."( Arrialexa)

Andy Lee
LTI Films
Tecnoir

'If it looks good , it is good!'


#3
Germy1979

Posted 12 November 2012 - 06:05 PM

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Jeff Cronenweth uses an 80D with the Red One MX. Schneider has a video from Nab 2011 of their "then" new nd's for matteboxes. They filter IR also,
(basically just for true blacks...) - so the selling point was a set of those would be the only filters you would need. All i saw in the video was a Sony EX3 turn a purple hat back into a black one when they stuck it on.

I have a Gh2, which sure as hell ain't an Alexa.. Lol.. I don't think i ever saw an issue like that or even thought about it being a problem until i started researching these filters.. Lol.

#4
QuickHitRecord

Posted 12 November 2012 - 06:29 PM

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Andy -- Interesting to read Roger Deakins' take. If he's able to create the images that he does without these filters, then I probably don't need them either. Thanks for sharing.

Germy -- I'm getting the feeling that these may be in the category of ultra-nitpicky control filters. It's hard to be too nitpicky when you're running a GH2 like we are!

#5
andy lee

Posted 12 November 2012 - 06:53 PM

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I wont be using one on my GH2 either
just NDs thats all I use

Andy Lee
LTI Films
Tecnoir

'If it looks good , it is good!'


#6
andy lee

Posted 12 November 2012 - 07:13 PM

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Jeff Cronenweth uses an 80D with the Red One MX. Schneider has a video from Nab 2011 of their "then" new nd's for matteboxes. They filter IR also,
(basically just for true blacks...) - so the selling point was a set of those would be the only filters you would need. All i saw in the video was a Sony EX3 turn a purple hat back into a black one when they stuck it on.

I have a Gh2, which sure as hell ain't an Alexa.. Lol.. I don't think i ever saw an issue like that or even thought about it being a problem until i started researching these filters.. Lol.


interesting read here on Cronenwerth with the Red One MX with an 80D filter to give more blue so he had more latitude...interesting idea!

http://www.icgmagazi...011/12/01/1787/

Andy Lee
LTI Films
Tecnoir

'If it looks good , it is good!'


#7
Germy1979

Posted 12 November 2012 - 11:01 PM

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interesting read here on Cronenwerth with the Red One MX with an 80D filter to give more blue so he had more latitude...interesting idea!

http://www.icgmagazi...011/12/01/1787/


That's pretty awesome....considering if one had four grand laying around, he could own the camera. Accessories are all over the place in the "red stuff for sale" thread at Reduser for great deals. I think the only reason there are still any available on Red is the fact that Redmags are RIDICULOUSLY expensive.
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#8
andy lee

Posted 14 November 2012 - 09:37 PM

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The Arri Alexa has an ISO of 800 so when you shoot outside you do need ND filters
once you go past 2 stops ND4 there is a slight colour shift especially in the blacks due to the NDs
so you do need to use a IR filter to correct this cast.
Had a good talk today with several DOPs on the Arri Stand at BVE North.
So there are a few ways of doing this!
Some use IR filters and some dont....
Its a personal choise thing!

Andy Lee
LTI Films
Tecnoir

'If it looks good , it is good!'






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