Infrared Cinematography

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Witold Plociennik

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Infrared Cinematography

PostFri Aug 22, 2014 7:45 pm

Hello.I wonder how to remove "ir low pass filter" from the camera Blackmagic 4k, becouse I would like the camera to see full visible spectrum and the infrared.
Does anyone know, how to do this operation? Is it possible in that camera? Thank you for all yours answers.
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Alastair Traill

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Re: Infrared Cinematography

PostSat Aug 23, 2014 1:33 pm

I do not know how to remove the IR cut filter from your BM 4k but I once tried to remove the filter from a defunct Sony PD 150 sensor. There seemed to be no easy way and I virtually chipped it out and never tried again. I was surprised at its thickness and seem to remember it consisted of two bits of glass cemented together. Had I been successful in removing the filter I would have had to find another piece of glass of the same properties to compensate for the removal of the filter. Without a substitute the lens-flange to sensor distance would have been incorrect.

I have done some IR work using cheap surveillance cameras. The advantage of the cheap cameras is that they have no IR cut filters whereas more expensive surveillance cameras may have filters that retract automatically with falling light intensity. I tried one of these and found that when the filter was automatically retracted the camera would decide that it was not so dark after all and put the filter back again. It would then remove the filter again and the cycle would continue. The most expensive surveillance cameras permit either manual or auto filter removal.

I now have two cameras that I hope to use for more IR work, one is a surveillance camera - the IOC ‘Orion’ CHDC-34BSDC and the other is a ‘C’ mount converted GoPro 3+ black that has a removable and replaceable IR cut filter.

Finally there is at least one business that modifies various cameras for IR use.
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Nikolay Smirnov

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Re: Infrared Cinematography

PostSat Aug 23, 2014 3:13 pm

As far as i know bmd cameras doesn't have any ir filtration. I've done ir video with my bmcc a couple of times.
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John Waldorff

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Re: Infrared Cinematography

PostSat Aug 23, 2014 6:41 pm

Really there is no filtration... I thought it was just quite low.

How to do the Infrared Cinematography then? Is it done in post and with the usual ETTR. Or are there special tricks?

Thanks.
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Alastair Traill

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Re: Infrared Cinematography

PostSun Aug 24, 2014 9:50 am

I have just done a quick test of my BMPCC using infrared illumination only. There was no sign of infrared sensitivity.
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John Waldorff

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Re: Infrared Cinematography

PostSun Aug 24, 2014 11:48 am

You could stick a 2.1 ND non IR block or even a 0.6+2.1 ND to have lots of IR pollution.
But if that is usable to be used as Infrared Cinematography.. I doubt.
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quantumrider

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Re: Infrared Cinematography

PostSun Aug 24, 2014 12:24 pm

so there is no need for infrared filter whatsoever on the packet?
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John Brawley

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Re: Infrared Cinematography

PostSun Aug 24, 2014 1:22 pm

The camera has a sensor cover glass which also blocks SOME IR.

You can remove the filter, its only held in place by a rubber O-Ring. ( I can't remember if it's the same on the pocket, I don't have one in front of me)

BE WARNED...

It means your sensor is NAKED and EXPOSED....

Normally the cover glass is fitted in a clean room environment so no dust settles on the sensor or the inside of the cover glass. If you remove it and replace it again, it's VERY VERY likely you'll get dust you won't be able to clean on your sensor or cover glass that will show up on your image at deeper F-stops.

JB
John Brawley
Cinematographer
London UK
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Alastair Traill

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Re: Infrared Cinematography

PostSun Aug 24, 2014 1:35 pm

It looks as though the IR cut filter is held in place by an 'O' ring on the BMPCC.
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quantumrider

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Re: Infrared Cinematography

PostSun Aug 24, 2014 1:37 pm

so how can we know for sure if there is no need for an additional IR cutter filter on the lens?
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DaleCampbellFilms

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Re: Infrared Cinematography

PostSun Aug 24, 2014 3:58 pm

You will need to remove the IR cut to do the kind of IR cinematography you seek.

I've had a few cameras modded in the past and the IR sensitivity of the Blackmagics as they stand is not close to cameras that have been modified. Once modded the cameras image is unusable for 'normal' footage.

Something else to consider as John mentions is the fact you are removing a protective glass cover by doing this, but also that piece of glass is a factor in how your lenses interact with the sensor. Without getting to technical most places that mod cameras for IR replace the filter with another piece of glass for protection and to keep the light getting to the sensor passing through the same amount of glass, sometimes this actually has some IR cut as people like different amounts of IR for different applications etc.
http://www.dalecampbellfilms.com

Blaine Russom

Re: Infrared Cinematography

PostSun Aug 24, 2014 6:04 pm

Get an IR-Pass filter and see how it goes.. then you'll know what to do form there.. you can also make your own..
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Nikolay Smirnov

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Re: Infrared Cinematography

PostSun Aug 24, 2014 6:54 pm

My old test with IR 720nm filter. I am now waiting for 680nm filter.

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Thomas Thiele

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Re: Infrared Cinematography

PostMon Aug 25, 2014 2:29 am

With pocket, no modification:
BMPCC, Lumix G3, GF3
pana 7-14, SLRM 12/T1.6, sigma 19, pana 20/1.7, pana 14-42, pana 45-150,
pentacon auto 29/2.8, 50/1.8, 135/2.8.
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Aaron Scheiner

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Re: Infrared Cinematography

PostMon Aug 25, 2014 12:58 pm

All the BMD cameras have an IR/UV cut filter installed... it's just inadequate (like many other CMOS cameras).

Removing the filter will change the optical path and unless you replace the glass with something else you won't be able to focus to infinity. I removed the IR cut filter from a Canon 350D a while back and this was one of the issues I encountered.

If the cameras really didn't have IR cut filters plants and black cloth would all appear bright purplish-brown without any filtering under tungsten and sunlight.

It is possible to film in IR with the cut filters in place if you shoot under direct sunlight and you use a fast lens (f/1.4 and faster). I tried this a while back with an IR-only filter on the lens.

IR photography and cinematography is a bit of a one-trick pony... it doesn't stay interesting for very long.
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Thomas Thiele

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Re: Infrared Cinematography

PostMon Aug 25, 2014 3:39 pm

Why it is not possible to get pseudo color IR pictures from te bmpcc?
For instance with my G3 I can get by choosing the right filter (750nm I think) pseudocolor IR.
This works because the blue channel (the green too, but much noisier) get the "pure IR" image. Which does not change with greater nm- filter, eg. 830nm). And the red channel get still enough visible red.
So the pseudo color ir is actually a two color picture with visible red in the red channel and pure ir in the blue (and green) channel. So sky gets red and chlorophyll and other gets bluish white.
With the pocket all channels "see" the same picture! Regardless of filter. (650, 715, 750, 830). The only thing changes is the generell brightness and the amount the red channel is more exposed and the IRish look slowly transform into a black and white red filter image by choosing lower nm.

It funny the blue channel do not differ from the red or green. When normalizing the channels you get a nearly perfect black and white.

That means that the blue channel and the green channel "see" visible red in the same amount as IR.
And this means also that there is a huge amount of color grosstalk and maybe can explain the orangish reds of the bmpcc.
BMPCC, Lumix G3, GF3
pana 7-14, SLRM 12/T1.6, sigma 19, pana 20/1.7, pana 14-42, pana 45-150,
pentacon auto 29/2.8, 50/1.8, 135/2.8.

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