IR Pollution Tests with Vari ND on BMCC and BMPCC

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Patrick Finnegan

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IR Pollution Tests with Vari ND on BMCC and BMPCC

PostSun Nov 10, 2013 7:08 pm

We have seen plenty of tests like the Abel Cine one with different versions of IR Cut filters to control infra red contamination on the Black Magic Cameras, both the Pocket Cinema Camera (you will find the results of these tests a little later in this thread) and the Cinema Camera. I have read conflicting reports on whether or not Vari ND's have the same issue with IR pollution as do regular ND's. Since I like the Vari ND's for run and gun work, I decided to test out two versions I use for IR pollution and color shift and thought I would share my findings.

Additionally, in this thread:

viewtopic.php?f=2&t=14889

I shared a technical paper sent to me by a sales rep from Tiffen explaining why a combination of IR cut and Hot Mirror were the optimum IR Pollution protection. I wondered how those same findings applied in the case of Vari ND's.

This is what I came up with...

Equipment tested in various combination:

1) Light Craft Workshop Digi Pro Vari ND: This is the newer and much improved version over the old one which gave very poor results. I was impressed with the testing I saw done on this and have been happy with its performance. I use a 77mm version which has 82mm outer threads.

2) A few years ago I found a Tiffen 4x5.65 Rota Pola on ebay for $30. I put it in the outer stage of my Chrosziel matte box and put a 4x4 circular pola on the inner stage . It is really versatile because I can rotate the inner stage to either cut out the polarizing affect if I am shooting talent and want to preserve skin highlights, or dial it in if I want to control reflections. Then I slip in the outer stage and dial down my exposure. I have found this combination to be really handy when I am built into Studio mode either on my BMCC, BMPCC or my Sony F3 and don't mind the bulk of a matte box.

3) Tiffen T1 82mm filter: From what I can gather, T1 was originally specifically developed for cameras like the Sony f35 which had effective sensor hot mirror IR protection above a certain wavelength (750nm) but were exposed in the near red spectrum. This filter apparently is targeted at a very narrow band of wavelength.

4) Tiffen 82mm Hot Mirror.(note the T1 and hot mirror were stacked on the outer stage of the vari nd during the testing, the hot mirror always placed on the outer most stage)

5) Tiffen water white irnd6 & irnd1.2, (both in 77mm screw on versions)

I. So first I set up a color chart, and some black synthetic and cotton cloth to establish the base line. I shot both at f22 (2 stops overexposed but the narrowest setting available on my lens) and at F2 with nine stops of regular ND filter (I stacked ND6,9 &1.2). From the following image you can see how intense the IR contamination is. I shot in video mode and did just some basic color correction to pull in some contrast and balance the levels. Even trying to pull down the red channel you can see how intense the color shift is:

IR Pollution reference.jpg
IR Pollution Reference
IR Pollution reference.jpg (523.35 KiB) Viewed 10406 times


II. Then I shot four versions with the LCW Vari ND. Going clockwise in the image:

1) Just dialing down exposure to an f2.8 with only the Vari ND.
2) Dialing to an f2.8 with Vari ND and T1.
3) Dialing to an f2.8 with Vari ND, T1 and Hot Mirror.
4) I decided to test using an irnd6 on the lens and putting the vari nd on after. The idea here being that in really bright conditions, I could use the irnd to cut a certain amount of light and then fine tune it with a more minimal dialing on the vari nd to see if that created any IR advantage. I added the hot mirror as well on the outer stage.

LCW Vari ND BMCC tests..jpg
LCW Vari ND
LCW Vari ND BMCC tests..jpg (392.27 KiB) Viewed 10406 times


From the color charts you can see that the combination of vari nd, T1 and Hot Mirror preserved the richest colors and retained the deepest blacks. Interestingly, trying to cut a certain amount of visible light with an irnd first and then just fine tuning with the vari nd seemed to be of no advantage (and in fact really was a disadvantage) as you can see a certain amount of shift in the black synthetic bag on the right that is not so in the case of the vari nd, t1, hot mirror version. You can also see from the reference shots that there is no where near the IR contamination with a vari ND as there is with regular ND's. The difference is dramatic.

III. Next, I shot the Rota Pola ND with my matte box. Since I don't have a three stage matte box nor do I have a 4x5.65 hot mirror or T1, I just tested this (going clockwise) by itself, with and irnd6 and irnd1.2 on the barrel. I also shot a reference of just using the rota pola at achieve an f22 (the least amount of polarization affect) to have as a comparison.

Rota Pola ND BMCC tests..jpg
Rota Pola Tests
Rota Pola ND BMCC tests..jpg (355.66 KiB) Viewed 10406 times


In this case it seems like the irnd6 combination with the rota pola fine tuning the exposure gave the truest colors in the chart There is still a slight shift in the blacks but nothing I couldn't dial out from a log file in Resolve. It seems the adding the higher irnd1.2 was less effective than using the rota pola, again leading me to believe that vari ND,s have less IR contamination issues than do regular ND's I suspect if I could have added a hot mirror to the outer stage I would have seen the black return to true black.


Final Conclusions:
1) As far as IR pollution goes for the cinema camera's sensor, from the dramatic shift to the red in the 1st reference shot, I suspect the Cinema Camera's sensor has very little IR protection compared with many other camera's (I saw this in Abel Cine's tests as well).

2) If you chose to use a vari nd to control exposure, while it introduces a certain amount of color shift to the green, it does a really nice job of controlling exposure without a huge price of IR contamination. Adding a T1 and Hot mirror seems to be the optimum solution (agreeing with Tiffen's findings) to solve what little issues it has and to my eye and from what I saw on my scopes, at least, it introduces the least color shift.

3) While the Matte Box Rota Pola ND was not as neutral as the LCW Vari ND in controlling exposure, knowing its limitations and how to combine it with some IR cut protection on the barrel I feel quite confident in using it when appropriate, particularly when shooting in log as I feel confident that I could correct in post the relatively minor shift to the green.

4) While shooting in raw would probably mitigate the need for concerns about color shift as you could dial the white balance after , I don't think it would solve the issue of the IR contamination and what it would do to certain fabrics. I would use the same protection.

5) And last, some feel that a Vari ND does a certain amount of degradation to the image, or image softening. I cannot repudiate or verify this, but the image from the BlackMagic is so sharp, I don't mind a certain amount of filmic softening to what it sees. My taste.

Hope this is helpful to some of you out there who have been asking some of the same questions as I have. Of course, for wide lenses (roughly 24mm and under) where vignetting can occur with pola's I will have to switich to conventional irnds in combination with the hot mirror.

Later in this thread you will find my results for another version of this test with the Pocket camera. I plan to shoot these same tests with my Sony F3 just to have as a comparison against a sensor that has more IR blocking filtering. I will share those findings as well when I get some time to post again if people are curious.
Last edited by Patrick Finnegan on Tue Nov 12, 2013 3:18 pm, edited 3 times in total.
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Re: IR Pollution Tests with Vari ND on BMCC

PostSun Nov 10, 2013 8:40 pm

Well might solve half the problem for me. I can't fit a hot mirror on my slim VND Singh ray but can get the 77mm Tiffen behind it...

Thanks for tests!
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 3:52 am

Thanks for your hard work. Very helpful. These tests are a lot of work.

Can you explain the actual different between the Tiffen T1 and the Tiffen Hot Mirror (the one w/o ND - as I already have Schneider NDs and a Schneider Vari-ND) … or, point me in the right direction? Is it that they suppress different IR spectrums? Would be nice to have T1 and the Hot Mirror in one filter. I wonder what the Vari-ND and Hot Mirror w/o the T1 would look like? I don't think you did that combination, but maybe I missed that.

Thanks!
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 5:13 am

Great info. Thanks for your time and energy Patrick. Interesting how it seems that the vari nds have less ir issues.
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 5:27 am

Thanks Patrick. I actually didn't like the one Tiffen IRND I tried on my Pocket, the 1.2. Pulled out too much red and shifted sky noticeably cyan.

The graph on page 2 of this pdf might explain why and answer some other questions about the different Tiffen filters. http://www.tiffen.com/userimages2/Filte ... _Broch.pdf

People should also be aware that the Pocket and the BMCC apparently react differently to IR. I only own the Pocket and I have tried up to 7 stops of ND with no IR filtration and with no visible IR contamination. That was in direct sunlight; artificial hotlights might be different. My best guess is that the extra cover glass in the throat of the mount on the Pocket accounts for the difference from the BMCC.

Looking forward to your tests.
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 6:52 am

Scott Stacy wrote:Thanks for your hard work. Very helpful. These tests are a lot of work.

Can you explain the actual different between the Tiffen T1 and the Tiffen Hot Mirror (the one w/o ND - as I already have Schneider NDs and a Schneider Vari-ND) … or, point me in the right direction? Is it that they suppress different IR spectrums? Would be nice to have T1 and the Hot Mirror in one filter. I wonder what the Vari-ND and Hot Mirror w/o the T1 would look like? I don't think you did that combination, but maybe I missed that.

Thanks!

You are welcome. Glad it could be of use.

From the research I have done my understanding is that yes, they do suppress different IR spectrums but by two very different techniques. Here is a press release from Tiffen explaining the T1 filter. It is very informative.

http://www.tiffen.com/press_release_T1IR_filter.html

From what I understand, there are basically two ways filter manufacturers block IR light, the first is through absorption (this is what you get in what are referred to as IRND's) and the second is through actually reflecting the infra red wavelengths ( this is what is referred to as a hot mirror or dichroic).

From what I understand the T1 filter was developed for cameras like the Sony F35 which have effective hot mirrors over the sensor for blocking higher wavelengths of infrared but were susceptible to contamination in a very specific band of wavelength in the near red part of the spectrum. With such contamination, blacks were a bit muddy and reds were muted.
If you had a Red or Ex1 or EX3, you would need to spend the extra money on adding a hot mirror (adding about $400 to the cost) component to your filtering as those cameras were not as effectively protected above 700-750nm where the hot mirror does its work. This is one of the reasons they are offered for purchase separately. I suspect that the BlackMagic cameras suffer from the same lack of hot mirror protection as do the Red MX etc...which is why in my tests the hot mirror/T1/Vari Nd combination seem to yield the truest colors.

The technical paper from Tiffen I uploaded in the (above referenced) thread:

viewtopic.php?f=2&t=14889

explains this pretty well, I believe. In the graphs you can see the various spectrums dealt with by forms of filtering. Plus the paper quoted by Steve above fills in a lot of the details as well.

The drawback to using a hot mirror is that if you are shooting cars or reflective surfaces or shooting nearly into a light source you have to be careful because you can actually get a mirror like reflection at times from the hot mirror drifting across your scene. The other disadvantage is that a hot mirror can only be mounted on the outer most stage of your filters (the one farthest from the lens) otherwise it can reflect back to the filters above it causing weird light distortions.

You can use an IRND (or absorption filter) on the inner stage of your filters and even stack regular ND's on top of it or under it with no ill effect, but it is not recommended to stack IRND's together.

So you can either purchase a hot mirror and IRND's separately or use an IRND Hot Mirror combination filter which is an IR absorption filter with a hot mirror built into it.

You are right I think I forgot to test for just the hot mirror without the T1. I will look through my footage and see if I missed it. If not, I will test that when I test my pocket cinema camera with these same combinations.
Last edited by Patrick Finnegan on Tue Nov 12, 2013 5:53 pm, edited 2 times in total.
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 7:02 am

Dwight wrote:Great info. Thanks for your time and energy Patrick. Interesting how it seems that the vari nds have less ir issues.


You are welcome. Yes, I was presently surprised to find that out. I had suspected it for some time but had to test to be sure.
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 7:03 am

Steve Wake wrote:Thanks Patrick. I actually didn't like the one Tiffen IRND I tried on my Pocket, the 1.2. Pulled out too much red and shifted sky noticeably cyan.

The graph on page 2 of this pdf might explain why and answer some other questions about the different Tiffen filters. http://www.tiffen.com/userimages2/Filte ... _Broch.pdf

People should also be aware that the Pocket and the BMCC apparently react differently to IR. I only own the Pocket and I have tried up to 7 stops of ND with no IR filtration and with no visible IR contamination. That was in direct sunlight; artificial hotlights might be different. My best guess is that the extra cover glass in the throat of the mount on the Pocket accounts for the difference from the BMCC.

Looking forward to your tests.


It will be interesting to compare the two cameras. Hope to get to it this week if possible.
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Re: IR Pollution Tests with Vari ND on BMCC

PostMon Nov 11, 2013 7:58 pm

Steve Wake wrote:People should also be aware that the Pocket and the BMCC apparently react differently to IR. I only own the Pocket and I have tried up to 7 stops of ND with no IR filtration and with no visible IR contamination. That was in direct sunlight; artificial hotlights might be different. My best guess is that the extra cover glass in the throat of the mount on the Pocket accounts for the difference from the BMCC.

Looking forward to your tests.



Steve, I would double check your findings. Make sure you have some synthetic blacks in the test because cotton doesn't really show the IR Pollution (in the images above I kept a piece of black cotton in the shot which doesn't change colors while the piece to its left changes dramatically). As you can see from the findings below there is substantial IR pollution affect on the Pocket Cinema sensor, as far as I can tell, the same as the Cinema Camera. I don't think either of these cameras (which I also understand lack optical low pass filters over the sensor) have much if any IR blocking filtration over the sensors.

These are the results of my tests with the Black Magic Pocket Cinema Camera.

First the reference shot. Again I shot the fabrics and color chart at an f22 to establish a reference. Even at f22 the shot was overexposed so I had to put in an ND3 to keep it from being overblown. What is interesting here is that even that little amount of ND is already showing the affect of IR pollution in the fabric to the right of the clapper, as opposed to the all cotton black cloths-pinned to the clapper. At F2.8 (I know it is labeled F2 but that was an error) with 6 stops of regular ND, the red shift in the black fabric is dramatic.


BMPCC Reference.jpg
Reference Shot
BMPCC Reference.jpg (269.18 KiB) Viewed 10220 times



Next I shot the same reference scene with the LCW Vari ND (going clockwise) with a T1, a Hot Mirror and with both the hot mirror and T1. The final frame is just the reference again at F22 with an ND3. I then brought all of the levels into a very quick balance in Resolve. These findings agree with the ones above. To my eye and the scopes, in spite of a slight shift to green with both the T1 and Hot mirror, that combination in conjunction with the Vari ND produces the truest blacks and colors.

That is what I am sticking with when I use the Vari ND for run and gun.



BMPCC Vari ND Tests.jpg
Vari ND Tests
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostMon Nov 11, 2013 8:04 pm

Thanks for the tests, Patrick.

Could you post a DNG of the HM + T1 + Vari combo? If possible.

Also, how does the contamination look when shooting with heavier ND? Say wide open at 1.4 or 1.8 (Not sure if your lens goes that fast), but still exposed properly via ND.

Is the green cast from your HM, T1? Or your Vari ND?

I agree on pocket contamination, it's there, certain types of materials show it worse than others.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostTue Nov 12, 2013 12:10 am

Thanks, Patrick. This is really helpful and for me, timely.

I never did catch what light source you were using for your tests.

My quick test had several black synthetics, black cotton and green grass, in pretty intense direct sunlight. There was a B+W Vario ND in the mix and that could have blocked at least some IR (a Schneider engineer told me that polarizers inherently block near-IR). Anyway, I don't doubt IR contamination can affect the Pocket, and from your tests it looks like it has no more protection than the BMCC. Seem every situation and combination of filtration is different. This is all new to me, though I understand the basic ideas from physics and shooting stills. I'm experimenting and sending stuff back for refunds when they don't work for me for any reason. I've settled on what I want to try next: Genustech eclipse with a dichroic IR that rolls off in the 650-700nm region in front, plus an empty polarizer frame mounted behind (so I can control the polarization of the fader). Trying to find a vary-ND solution that works.

I can't agree that "cut"=absorption. Schneider Tru-Cut filters are dichroic (=hot mirror) and Schneider Platinum are absorption type. "Cut" as far as I can tell is really a way to distinguish filters that filter out IR from those that pass IR (for IR photography). I think some confusion could be avoided if we just distinguished the two types as "absorption" or "dichroic = hot mirror = interference" I understand that "cut" may be the same as absorption in many people's understanding, but as with Schneider's naming system it can be confusing too.

BTW, you might want to take a look at these since to my reading they counter what you've said about RED's IR problems:

http://alfonsoparra-development.s3.amaz ... num_ev.pdf
http://provideocoalition.com/aadams/sto ... _solved/P2
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostTue Nov 12, 2013 4:43 am

Kholi wrote:Thanks for the tests, Patrick.
You are most welcome. Thank you

Could you post a DNG of the HM + T1 + Vari combo? If possible.

Will try to get to that next chance I can.

Also, how does the contamination look when shooting with heavier ND? Say wide open at 1.4 or 1.8 (Not sure if your lens goes that fast), but still exposed properly via ND.

I posted a frame grab of 9 stops of ND at an F2 in the opening of the thread. My lenses actually do go to a 1.4 but I felt with the dramatic IR pollution at an F2 was evidence enough of where things are headed. More ND's would have meant even more IR contamination.

Is the green cast from your HM, T1? Or your Vari ND?

I suspect both the Vari ND and the T1 introduce a certain amount of color shift. Again, I felt it was something I could easily dial out in post as it was an overall effect...unlike the IR contamination which although overall also affected certain elements of the scene more than others.I simply could not dial it out of the fabric for instance. Didn't try a secondary color correction on it though.

I agree on pocket contamination, it's there, certain types of materials show it worse than others.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostTue Nov 12, 2013 5:06 am

Hey Patrick,

Thanks! The T1 alone actually looks better than the HM alone on both the Pocket and the Cinema Camera. That's interesting.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostTue Nov 12, 2013 5:12 am

Steve Wake wrote:Thanks, Patrick. This is really helpful and for me, timely.

I never did catch what light source you were using for your tests.

Hi Steve,
I shot in direct exterior sunlight...no window glass to confuse the findings.

I can't agree that "cut"=absorption. Schneider Tru-Cut filters are dichroic (=hot mirror) and Schneider Platinum are absorption type. "Cut" as far as I can tell is really a way to distinguish filters that filter out IR from those that pass IR (for IR photography). I think some confusion could be avoided if we just distinguished the two types as "absorption" or "dichroic = hot mirror = interference" I understand that "cut" may be the same as absorption in many people's understanding, but as with Schneider's naming system it can be confusing too.

Thanks for the clarification. I do so much research on all of this, at times some of the nomenclature spills over in my thinking. You are right. It would be more clear to just talk about absorption and reflection as the two ways I know of that IR contamination is handled by filter manufacturers. I have corrected my post

BTW, you might want to take a look at these since to my reading they counter what you've said about RED's IR problems:

http://alfonsoparra-development.s3.amaz ... num_ev.pdf
http://provideocoalition.com/aadams/sto ... _solved/P2


Very helpful articles. I had previously stumbled on Art Adams post but couldn't find it for the life of me when trying to come up with the answers for the questions I was getting.
Yet again, another example of transposition of concepts in my mind. I thought the EX!, EX3 and the Red MX were the cameras that had the hot mirror protection. Sounds like it is just the opposite. Apparently it is the Sony F35 and Alexa, while the Red, etc lack protection above 750nm and therefore needs the hot mirror added. Again, corrected my post. Thank you very much for the clarification.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostTue Nov 12, 2013 5:40 am

Scott Stacy wrote:Hey Patrick,

Thanks! The T1 alone actually looks better than the HM alone on both the Pocket and the Cinema Camera. That's interesting.


Yes, from Abel Cine's tests it seems the dye Tiffen uses in its filters, while looking too greenish blue on other cameras, seems to produce a nice neutral balance on the Black Magic cameras. The slight cyan in the T1 seems to counter the orangish red of the near red IR pollution pretty well. i think the addition of the hot mirror just adds a little extra help above 750nm, far red. What surprised me was how little the addition of an IRND .6 with the vari ND made any effective color adjustment. It seems (as Steve Wake was told above by Schneider), the polarizers in Vari NDs inherently cut IR in the near red part of the spectrum, and since the T1 is designed to cut a narrow band between near red and where a hot mirror cuts in for far red, it seems like the perfect addition to a Vari ND used in combination with the sensor on the BlackMagic...but that is just a guess on my part...no science to back it up from Black Magic. It would be great if they could weigh in on what IR protection if any they build into the sensor.
Again obviously since vari NDs vignette and give the dreaded cross X with wide lenses you have to revert to normal IR nd's and hot mirrors for anything as wide or wider than (roughly) a 24mm.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostTue Nov 12, 2013 11:25 am

Hi Patrick. Very interesting, thanks for sharing.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostWed Nov 13, 2013 11:06 pm

Patrick Finnegan wrote:Again obviously since vari NDs vignette and give the dreaded cross X with wide lenses you have to revert to normal IR nd's and hot mirrors for anything as wide or wider than (roughly) a 24mm.


Again, what an awesome review you have done here.

Yep, the problem I run into is that my Arri matte box only has room for two 4x5.65 filters (a ND and an IR filter). Looks like I will pick up the pricey T1. When I can get away from my mattebox and use a prime lens and a vari-ND, the dreaded vignetting issue comes up on wider lenses when trying to use the T1 with the pretty thick Hot Mirror :(
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostThu Nov 14, 2013 1:28 am

Scott Stacy wrote:
Patrick Finnegan wrote:Again obviously since vari NDs vignette and give the dreaded cross X with wide lenses you have to revert to normal IR nd's and hot mirrors for anything as wide or wider than (roughly) a 24mm.


Again, what an awesome review you have done here.

Yep, the problem I run into is that my Arri matte box only has room for two 4x5.65 filters (a ND and an IR filter). Looks like I will pick up the pricey T1. When I can get away from my mattebox and use a prime lens and a vari-ND, the dreaded vignetting issue comes up on wider lenses when trying to use the T1 with the pretty thick Hot Mirror :(


I just found one of these on ebay

http://www.ebay.com/itm/140976576678

82mmfilterholder-1logo.jpg
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Although they are designed to fit into one of the matte box stages I plan to velcro the holder onto the outer plate of my matte box and use it to affix my 82mm hot mirror beyond the filter trays. Since the Hot mirror always wants to be on the outer most stage this should free up the slots of my matte box for other things I need filter wise. I think an added bonus is that it will screen out unwanted light from around the circular lens in the square glass and opening potentially reflecting among the stages of glass. I will post results of it when I build it and try it out. Additionally, 82mm filters are much cheaper and easier to come by second hand than 4x4. I got my 82mm hot mirror for $70 off ebay.

You could also stack a Ti and Hot Mirror in 82mm if you chose.
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Re: IR Pollution Tests with Vari ND on BMCC and BMPCC

PostThu Nov 14, 2013 3:15 am

Hmmm … that looks interesting.
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4x 2TB NVME M.2 Samsung 970 (RAID10)
Decklink Pro 4K
Areca 1883 48TB RAID6

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