IR Pollution on Pocket 6k Pro

Hi,

I’ve been enjoying getting used to my Pocket 6k Pro, but I have noticed what looks to be some IR pollution when using the internal ND filters.

This is a quick test against the C100 MKii (both with 6 stops of ND):
https://vimeo.com/520358521/2ab5a0a673

Does this look normal or do you think I’ve got a defective unit? I'm trying to decide whether I need to send it back to get looked at.

As you can see on the shots below, certain things like the black tyre and trampoline look fine but other things like the case, remote and black DVD cover look to have a redish tinge. It's not super noticeable but it's there. Not sure how this compares with other units of the same model or a 6k with a screw on IRND.

Any thoughts/feedback appreciated.

Many Thanks,

Matt

In the video, you didn't show a Log to extended video version of the 6K shot without ND, and the Canon shot appears to be non-normalized LOG, so there's really nothing against which to make a fair comparison.

To my eyes, it looks more like the characteristics of extended video with Gen5, rather than IR pollution. But without more information....

Even if there is some IR pollution related to the internal NDs, it's unlikely that sending the camera in will fix it.

There are at least a couple of youtube videos of people testing the internal ND delivering cooler images than clear mode turned out the internal ND being IR cut were correcting the WB and that in clear mode is actually warmer and suspect that was due to IR pollution not being blocked. You should be seeing the opposite.

There are at least a couple of youtube videos of people testing the internal ND delivering cooler images than clear mode turned out the internal ND being IR cut were correcting the WB and that in clear mode is actually warmer and suspect that was due to IR pollution not being blocked. You should be seeing the opposite.

I thought the entire ND mechanism was behind an IR glass?

In the video, you didn't show a Log to extended video version of the 6K shot without ND, and the Canon shot appears to be non-normalized LOG, so there's really nothing against which to make a fair comparison.

To my eyes, it looks more like the characteristics of extended video with Gen5, rather than IR pollution. But without more information....

Even if there is some IR pollution related to the internal NDs, it's unlikely that sending the camera in will fix it.

Thanks John. The Canon footage was shot in Wide DR which is like their version of extended video. I don't normally shoot log with it because it's only 8 bit. I put it in there as I know there's no colour shift between ND and clear.

As you suggested, I had another look and I can't see much colour shift between clear and the various stops of ND on the 6k Pro.

The LUT is just the Blackmagic Film to Extended Video so I wouldn't have thought that caused a colour shift. If I don't apply the LUT and just add contrast and saturation then we get that same slight reddish tinge on the blacks.

If Tom is right and the entire mechanism is behind and IR glass, my guess would be that it cuts most of the IR pollution but not quite all of it, which is why it is visible on certain black items. Might be wrong though

I think it's best to redo these tests but with black fabric. This is where I've noticed it to be most prevalent in older Pocket 6K.

I think it's best to redo these tests but with black fabric. This is where I've noticed it to be most prevalent in older Pocket 6K.

Good idea Will. I'll try do that over the next week or so when I get chance. Cheers

The built-in IRND filters attenuate the infrared light to the same degree as they reduce visible light. So they are not aggressively cutting all infrared. Some material such as black nylon seem to generate a lot more infrared than other dark material. But the material doesn’t have to be black, since we all know green leaves on trees also radiate infrared light.

So it is possible that the built-in filters work well in most situations but there may be times when an IR Cut filter is needed. The reason the IRND filters aren’t more aggressive is that they are designed to complement skin tones which can suffer some with an IR Cut.

The built-in IRND filters attenuate the infrared light to the same degree as they reduce visible light. So they are not aggressively cutting all infrared. Some material such as black nylon seem to generate a lot more infrared than other dark material. But the material doesn’t have to be black, since we all know green leaves on trees also radiate infrared light.

So it is possible that the built-in filters work well in most situations but there may be times when an IR Cut filter is needed. The reason the IRND filters aren’t more aggressive is that they are designed to complement skin tones which can suffer some with an IR Cut.

Thanks Rick, that makes sense. Generally speaking, I'm quite happy with the internal NDs and I'll probably pick up an IR cut filter for those times when it is needed.

If you chose to redo the tests consider using a white reference card, neither camera seems to have the correct WB.

Compare the same lens and stop. In the video there is a strong vignette on the P6k indicating that the lens is WFO. The Canon shot exhibits none of these signs. There’s about 2 stops of falloff with the P6k that is enhancing an already significant color difference.

The neutral transform is G5 to Video, the Extended Video G5 transform is a slider preset for G5 film.

Good Luck

If you chose to redo the tests consider using a white reference card, neither camera seems to have the correct WB.

Compare the same lens and stop. In the video there is a strong vignette on the P6k indicating that the lens is WFO. The Canon shot exhibits none of these signs. There’s about 2 stops of falloff with the P6k that is enhancing an already significant color difference.

The neutral transform is G5 to Video, the Extended Video G5 transform is a slider preset for G5 film.

Good Luck

Thanks for the tips Howard. I'll keep this in mind.

I got a 1 stop Hoya ProND to intercut with the internal ND so instead of 2,4,6 stops I now have 1,2,3,4,5,6,7 stops. I will find out how much it going to affect WB using this method.

Adding a magenta tint of 10 is going to exacerbate existing IR pollution, especially at higher ND stops. Try going the other way – add green tint between −10 and −25.

Additionally, Blackmagic cameras, for reasons unclear, are weak in two major aspects – IR-blocking coating of the sensor glass and the lack of an OLPF. So, the current solution to address minimal or significant IR pollution, in my experience, is to shift the midtones towards green or simply add green tint in post.

Pushing towards green will seem odd in the beginning, but only because of the mere-exposure effect most of us are unaware of – all modern camera sensors and consumer display screens are, unfortunately, magenta-biased. You can check this yourself on your smartphone, external monitor, or your laptop screen – open a fullscreen all-white blank webpage or JPEG, or play a white-screen video on YouTube and hold a sheet of A4 paper beside it in direct sunlight – the screen will appear pink.

So it’s safe to assume that any footage that is pushed towards the red-end of the visible spectrum, and especially that which contains IR pollution above 650 nm, will be appear terribly magenta on any major display screen.

... Blackmagic cameras, for reasons unclear, are weak in two major aspects – IR-blocking coating of the sensor glass and the lack of an OLPF...

This was explained around 2012. It’s by design and completely intentional, not an oversight.

OLPF and the lack thereof:
In designing a camera (BMCC 2.5K) that would shoot lossless raw (as well as ProRes), it was decided to have an image that was as sharp as possible compared to other cameras that included an OLPF. There are many ways to soften a sharp image temporarily when that is desired including by the use of filters in front of the sensor or in front of the lens for example when there’s a creative reason to soften the image. The downside was the increased possibility of moiré which sometimes can be eliminated by changing your distance to the subject; not always an option of course especially when shooting subjects wearing clothes that are prone to moiré and you just can’t ask the groom to change his outfit during a wedding shoot.

Sensor cover glass IR filtration:
Again the original camera was called the Blackmagic Cinema Camera and it was designed to produce gorgeous skin tones naturally, by which I mean, the raw image wasn’t going to enhance colours by processing of the image in camera as might occur in other cameras to create a more pleasing and saturated look. BMD recognized that digital sensors are more sensitive to infrared wavelengths than was true with the celluloid film that ‘cinema’ implied at the time. Infrared doesn’t begin at 650nm, closer to 700nm. However many IR Cut filters begin about 650nm, as you know, with about 680nm being the midpoint of the filtration. However that really is cutting deep red. Regardless of your subject’s skin colour, deep red wavelengths are an important component in arriving at a pleasing but natural skin tone.

And so BMD designed a sensor glass filter with mild infrared attenuation to let in deep red to produce great skin tones. The downside can be evident of course when you are shooting many scenarios that include other subjects including landscapes or certain materials prone to radiating infrared such as nylon or rayon. For that additional IR filtration is required in front of the lens generally; that can mean an IRND or an IR Cut (which work differently).

Now this design philosophy has continued on all BMD cinema cameras. Hope this explanation gives you an understanding of their design rationale. It isn’t meant to argue BMD is right or wrong and for the most part, the shooter can work with the limitations either on camera (infrared filters and moiré) or in post (softening an image).

Adding a magenta tint of 10 is going to exacerbate existing IR pollution, especially at higher ND stops. Try going the other way – add green tint between −10 and −25.

Thanks. I understand what you're saying. Initially I'd just selected the daylight preset on the camera, which sets the WB to 5600 and adds the magenta tint, but I'll certainly do some tests without the tint or pushing towards green.

Thank you for elucidating the rationale, Rick. I was perplexed for ages about it.

I’d still firmly argue that cinema camera-design philosophy must favour an OLPF with a strong UV- and IR-blocking coating, with transmittance between 410 and 670 nm.

Regarding moiré and aliasing, I’d go along working around them only when they overwhelm a camera’s OLPF. In the absence of an OLPF, the distraction they create in the footage is dispiriting. Nevertheless, I find myself not entirely unhappy disregarding my Pocket 4K’s moiré issues, which, although not negligible, can generally pass unseen.

And pleasing but natural skin tone still looks pleasing and natural to me without the extra red, but as you know, these things are deeply subjective.

I remember chuckling in agreement as David Fincher mockingly criticised display manufacturers in an interview for injecting magenta in the white point under the assumption that that pink-looking skin automatically makes people look healthy and happy. He said he hates that, and I couldn’t agree more, though it seems like he prefers to push midtones towards yellow instead of green. I admit – I can’t help feeling vindicated for sharing a minor sensibility with one of the most acclaimed directors of all time.

All good... and then there’s Mank.

Adding a magenta tint of 10 is going to exacerbate existing IR pollution, especially at higher ND stops. Try going the other way – add green tint between −10 and −25.

Thanks. I understand what you're saying. Initially I'd just selected the daylight preset on the camera, which sets the WB to 5600 and adds the magenta tint, but I'll certainly do some tests without the tint or pushing towards green.

I’d add that rating the white balance between 4000 and 4400 K is also helpful, even for daylight, along with adding the green tint. The more you shift the white balance and tint towards blue and green, the more likely it is that moderate IR pollution can be mitigated.

And so BMD designed a sensor glass filter with mild infrared attenuation to let in deep red to produce great skin tones.

Rick makes a great point.

BMD cameras DO HAVE AN IR FILTER, it's just that it's mild enough to favour letting in more of the spectrum. If you want to take more out use a good full spectrum ND or even a straight IR cut filter.

JB

I got a 1 stop Hoya ProND to intercut with the internal ND so instead of 2,4,6 stops I now have 1,2,3,4,5,6,7 stops. I will find out how much it going to affect WB using this method.

I've found the HoyaPro ND to be amongst the most neutral of the inexpensive screw in photo ND filters.

JB

I’d add that rating the white balance between 4000 and 4400 K is also helpful, even for daylight, along with adding the green tint. The more you shift the white balance and tint towards blue and green, the more likely it is that moderate IR pollution can be mitigated.

Thanks. I'll bear this in mind.

Here's a test that someone did on the internal NDs. He said there was very minimal colour shift; not really noticeable at 2 or 4 stops and easily correctable at 8. There was no more colour shift than the external NDs he tested against.

He mentioned that his only issues are the white balance on the LCD and not being able to import LUTs.

I've not tested trying importing LUTs, but I can't seem to delete presets. Even when I confirm and click the delete button the preset doesn't delete. Does anyone else have that issue?

This is a very minor thing and hopefully easily fixed with firmware.

Regarding the white balance on the LCD screen, mine doesn't seem to be off by anywhere near as much as what some people are saying so hopefully any firmware fix won't overcorrect and will just be a case of making sure all the monitors are calibrated the same.

I've found the HoyaPro ND to be amongst the most neutral of the inexpensive screw in photo ND filters.

JB

Hoya Pro ND filters are labeled as "Pro Imaging & Cinema", they are highly rated. I'm slowly building up the range of 82mm with step up rings.

In depth review here which talks about ir pollution

Sent from my iPhone using Tapatalk

In depth review here which talks about ir pollution

Sent from my iPhone using Tapatalk

Here's a link to the part of the video which talks about IR pollution (it's at the 20 minute mark):

In terms of doing another test, I don't think I have much to add to this. I agree with him that the effects of IR pollution can be visible on certain black fabrics. I understand what other users have said about the camera prioritising skin tones and if I find the IR too noticeable for certain shots then I'll use an IR cut filter or low strength IRND for those shots. For me it's not too much of an issue.