Thread: Ursa Mini Pro - IR Cut on 'Clear' Filter?

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  1. #1 Ursa Mini Pro - IR Cut on 'Clear' Filter? 
    Sorry if this has been answered before; I've seen it asked before but didn't see an official answer. I tried to ask this over on the official BM forum, but I guess a moderator has to approve my post, and has decided not to...

    So does the 'clear' filter on the Ursa Mini Pro block any IR as well? I know it's been stated that the 2, 4 & 6 stops NDs are IRNDs. I notice IR pollution on my Mini 4.6k even without any additional NDs, so I always have a Hoya IR cut on. It would be a major bummer (for me, at least) if the clear was actually clear and didn't have IR cut built in.
    Last edited by mstrouty; 03-20-2017 at 08:05 PM.
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  2. #2  
    Senior Member Timothy Cook's Avatar
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    Someone may be able to chime in and correct me if I'm wrong, but I think the BMD cameras are all balanced for daylight (actual sun) 5100k-5500k. So having the clear sensor non IR cut is relative right?

    Meaning that in daylight you won't need a IR cut unless adding NDs, and you won't need a IR cut without NDs unless you are shooting under strong tungsten lights which can produce a lot of IR.

    Whenever I shoot outside and stopped down enough that I don't need a ND filter, with the Micro I get very clean blacks and color balanced image. But as soon as I try the same thing under some really strong tungsten lights I have then I get very strong IR contamination and I have to use my IR cut.

    So it could be that the clear filter is just that, and BMD doesn't want to cut needed IR on your neutral shoots. (You do need balanced IR in you shots)
    This maybe the reason when shooting on Sony's and others that never really need a IR cut filter, because they have a strong one built in, you always get sort of pasty yellowish green skin that seems unnatural.

    I may be totally wrong but it seems like BMD always tries to give the operator the option to filter the image only when needed and only when the operator wants to.
    Once again I could be totally wrong.
    Last edited by Timothy Cook; 03-20-2017 at 08:03 PM.
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  3. #3  
    Fair enough, I understand BMD wants to give people 'filtration choice' and some people may not care about a bit of IR. I will say that the IR pollution (without additional NDs) was never terrible, but I had better blacks and skintones on Daylight and Tungsten sources with an IR cut added.

    Here is a quick test I did almost a year ago when I first had my camera that convinced me to always leave IR cut on (natural daylight was the main source). I've accidentally left IR cut off a couple times on some interviews over the past year and always had more trouble wrangling in skin tones.

    http://www.bmcuser.com/showthread.ph...l=1#post203912

    I guess at this point, I can see why BMD would include IR cut on the clear filter (for people like me who think it's needed) or I can see why they would leave it off (to give people the choice). I'd just like confirmation one way or the other. For me, the built in NDs would lose most of their appeal if still had to deal with an IR cut on clear shots.
    Last edited by mstrouty; 03-20-2017 at 08:20 PM.
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  4. #4  
    Hi!
    I was at the BM tour day in Vienna and asked a rep. If there's IRcut at the clear position. He said YES.
    Christian Haake / cinematographer / Austria / www.christianhaake.net / Reel: https://vimeo.com/208444259
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  5. #5  
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    Hi all,

    I think there's some misconceptions about IR. All Blackmagic cameras (and presumably all major cameras from any manufacturer) will have an IR filter. This is the blue glass you can see in front of the sensor on your Blackmagic cameras. The IR filtration is designed to make sure that the colour balance is correct for the sensor. Without this, skin tones for example, would look too magenta, or with too strong a filter they won't have enough magenta, and as mentioned will likely look too yellow/green. If you're seeing IR pollution without any other filters in front of the sensor it's probably due to a large imbalance of IR in the scene you are shooting, most likely due to the kind of lighting being used.

    Whilst I don't have the specs of the clear filter glass on the filter wheel, it doesn't need any extra IR cut because there's already the correct amount of IR filtration in the existing IR filter glass that all of the Blackmagic cameras have. I think it's important to make a distinction between IR cut filters and IRND filters. The ND filters on the URSA Mini Pro don't just simply cut IR, they are designed to cut the IR equally to the visible light so that the the colour balance remains the same with or without the NDs. If you are having to use an IR cut filter in front of your lens, I would still expect you'll need to use it when using the ND filters.

    So to answer the original question, yes there is IR filtration when not using the NDs on the ND filter wheel, but it would be fundamentally the same as using your URSA Mini 4.6K without your IR filter. It would not make sense to add extra IR cut to the clear filter glass because with that the colour balance would be incorrect in more situations than it would without it.
    Chris Pearse
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    Blackmagic Design Japan
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  6. #6  
    Quote Originally Posted by ChrisPearse View Post
    I think there's some misconceptions about IR.
    No, there are no misconceptions... I own an Ursa Mini 4.6k and I understand that it has some IR control built in to either the sensor or olpf, much like any camera. I just find this filtration much to weak for my needs. I find that skin tones and blacks are better with 'additional' IR cut filtration, with pretty much any lighting source (daylight or tungsten).

    BMD and other folks may disagree with me and that is fine. I have done my own test and reached my own conclusions, so I don't think anyone is going to convince otherwise.
    Last edited by mstrouty; 03-21-2017 at 07:06 AM.
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  7. #7  
    Senior Member rick.lang's Avatar
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    Quote Originally Posted by Christian Haake View Post
    Hi!
    I was at the BM tour day in Vienna and asked a rep. If there's IRcut at the clear position. He said YES.
    No, there is no IR Cut in any of the built-in Mini Pro filters. Must be a misunderstanding.
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  8. #8  
    Quote Originally Posted by rick.lang View Post
    No, there is no IR Cut in any of the built-in Mini Pro filters. Must be a misunderstanding.
    Surely the 2, 4 and 6 stop are IRNDs. I thought that had already been confirmed
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  9. #9  
    Senior Member rick.lang's Avatar
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    Chris is stating BMD's approach correctly and I don't think the clear filter has any infrared attenuation since the sensor glass covers nclude light infrared protection. But in my own tests using IR Cut filters I've seen a difference in the scene when there is enough infrared radiation to be a concern. I've seen the need to clean up some blacks in synthetics for example, but my two tests didn't emphasize skin tones. Again, I'm of the school that thinks IR Cuts can be detrimental to skin, taking out the variations enhanced by deep red wavelengths.

    I'd be interested in seeing posts with skin tones, primarily faces, dark skin and light skin, where a heavy IR Cut improved skin tones.
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  10. #10  
    Senior Member rick.lang's Avatar
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    Quote Originally Posted by mstrouty View Post
    Surely the 2, 4 and 6 stop are IRNDs. I thought that had already been confirmed
    That's correct as Chris explained. IRND filters like BMD use and NiSi and others are there to attenuate visible and infrared wavelengths equally. An IR Cut eliminates IR with a steep drop off to zero in the spectral response at 680nm typically for BMD sensors. Other filters Cut about 700nm or 715nm or 750nm... different cut for different purposes.
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