Solving the Mixed Light Problem

[jplaurel 46]

I replied to someone heading to Socorro in another thread, but I decided this topic was worth its own thread, since so many people struggle with this issue.

Since I started shooting video underwater, I've been bedeviled by the mixed light problem. Years ago, few cameras apart from Canon DSLRs could dream of being able to white balance at depth. Then, along came the Panasonic GH5, and slowly camera makers followed suit. But what about supplemental light?

The problem is that when you're white balanced at depth, the output of 5600K video lights look red. If you white balance to 5600K to match your lights, then the ambient color looks terrible. And unlike strobes, almost video lights almost never have the sheer power to overwhelm daylight enough to get good color unless you're very close to the subject. What you really want is nice ambient white balance, and supplemental light that looks "normal", i.e., like natural light at depth.

The secret is to white balance for the ambient light at depth, then adjust your video lights so their output matches the ambient light color temperature. That way, you get a nice, colorful ambient light exposure, with a little more light on things close by to bring out detail and color, but without any weird color casts. For example, consider filming sharks. Ambient light only with a good white balance may look good when filming them from the side, but when the animal swims over you, it becomes a silhouette. It's alot nicer to throw some light onto the shark's belly so you can see some detail. But if you add light from normal 5600K video lights, it looks all red or pink. You want it to be white. And even though you can get a nice shot of sharks from the side with ambient light only, without extra light, you miss out on the beautiful iridescent colors in their skin. With good light, you will see flecks of gold and other colors in their skin as they swim by.

Around 8 years ago, Keldan released cyan heads for their original Luna 8 lights, and few people took notice. I remember then Nauticam rep Chris Parsons lamenting that he was having a hard time getting people to understand the idea of using cyan video lights to get better color underwater. After all, isn't a lack of red in underwater daylight the problem in the first place?

I was an early adopter of the Keldan cyan idea, but I never could get it to work very well with my GH4 (w/red filter) or the GH5 (without red filter, as it could white balance at depth on its own) Even with the GH5 white balanced at depth, I could never get really clean whites.

I was in the Revillagigedos a few weeks ago, and finally had some success getting decent ambient color with a mix of ambient and supplemental lighting. The rig was:

• Sony α1
• Nauticam NA-α1 housing
• Sony FE 28-60mm F4-5.6 
• Nauticam WWL1-B wet lens
• Keldan Spectrum SF -2 red filter (a frameless filter placed between the flat port and the WWL-1B)
• Keldan 4X lights with SF-12 Ambient filters.

I shot mostly Slog-3, but I also tried HLG. My experience was that, with Slog-3, I was at 6400-12,800 alot of the time in order to punch through the red filter and at the same time overexpose by about 2 stops required by this profile. This means quite a lot of noise, but Neat Video does a good job of cleaning it up.

I shot one dive at the boiler with HLG3, and I think going forward that will be my go-to profile. You don't have to overexpose it, so noise is less of an issue. If you nail the white balance, you get very nice color and good dynamic range. But remember that you have a little less room to work with it than slog-3. Still, HLG3 grades very easily, once you drop a corrective LUT onto the clip (I use the Leeming LUTs). Once that's done, I found that only minor corrections to contrast and exposure and saturation were required. Simple corrections and easy to do. Another benefit of HLG3 is that you can use the footage later to deliver for HDR displays, if you like. Here is the workflow for HLG in Final Cut Pro. My advice is to try HLG3.BT2020 in XAVC 4K S-I at 60P, 10 bit 4.2.2

For Slog-3, I am using the Phantom LUTs, and have found that the "Ice Blue" LUT works beautifully for underwater footage. After applying the LUT, only minor corrections to contrast, saturation and exposure were needed. Just a few clicks...

The Keldan system is brilliant. I was able to get nice color with ambient light at the Canyon cleaning station, where you will be at 80-90 feet. It's nice to have good ambient color and be able to put some light on the animals without the red cast. With the Keldan red filter (on your lens) and cyan filter on your lights, you get a nice clean look.

I credit a deceptively simple little tool for making my life underwater alot easier. If you're serious about video, YOU MUST have a good gray card at a minimum. And a color checker is also very useful as a color reference when finishing your footage. The Keldan color checker/white balance card was INDISPENSABLE. I had it on a small retract, so I could just grab it for white balance, and I'd also sometimes flip it over to show the Xrite color checker side at the beginning of a shot. I hold it at arm's length for white balance. Really, I cannot emphasize how valuable this thing is. Don't think, just buy it and thank me later.

The attached video shows my wife, Karin, photographing a silver tip at the Canyon. It was shot in slog-3, probably at about ISO 3200 or 6400, XAVC 4K S-I (600 mbps), 10bbit 4.2.2 at 60-FPS. Noise reduction with Neat Video. Keldan SF-2 red filter, and Keldan SF-12 cyan light filters on Keldan 4X compact lights. Depth was 85-90 feet, proving that the SF-2 (rated for 2-15 meters) and SF12 (rated for 10-18 meters) work  well together, even beyond their respective depth ratings. Notice that the lights don't have an overly warm cast, even though at 30,000k, the light temperature is a little lower than ambient. I found the SF-2/SF-12 filter system to work well from safety stop depths all the way down to 100ft.

Edited May 3, 2022 by jplaurel
corrections

[rileym21 0]

Very interesting! I'm in the very early stages of learning about this. I just got my first underwater housing and I'm starting with ambient light only. I'm sure I will be working through this mixed light problem soon, thank you for sharing your formula!

[dreifish 362]

Anyone figure out a good combination of Lee color gels to use on 6500k torches to bring the colour spectrum to something resembling ambient at 6-12m depth? Not all of us use Keldan lights

I might have to do some experiminetation. These two look promising as a starting point: 132 Medium Blue & 200 Double C.T. Blue

[rgilkes 11]

Worth noting that Sola Pro 15Ks also have blue and green filters available now. I have not used them yet, but will soon.

@jplaurel thanks for the comment about using Neat Video for noise reduction. I almost never use my Keldan red filter because it cuts down on so much light and I hate bumping my ISO so high and also my A7SIII does great white balancing underwater. I will give Neat Video a try.

Edited May 5, 2022 by rgilkes

[jplaurel 46]

2 hours ago, dreifish said:

Anyone figure out a good combination of Lee color gels to use on 6500k torches to bring the colour spectrum to something resembling ambient at 6-12m depth? Not all of us use Keldan lights

I might have to do some experiminetation. These two look promising as a starting point: 132 Medium Blue & 200 Double C.T. Blue

I would love to know this as well. It would give new life to some of my old lights, like the old Sola Video 2000. Given the cost of the Lee filters, though, I was thinking that maybe a good option would be to buy a pair of the "bluewater dome port cover" for $39 each that L&M make for the Sola 15,000. I think those Sola 15,000s are pretty big, so they could probably be jury-rigged to fit her lights. You could even cut them down to size for something like the old Solas. At least with these, the only work would be getting them attached in some way. The light color should be perfect, assuming the Sola 15,000 is 5600K.

Bluewater Dome Port Cover for Sola Video 15,000

Edited May 5, 2022 by jplaurel

[hyp 111]

I think a 2000lm light won’t have enough output to use with a filter. It barely has enough without one. 

[jplaurel 46]

14 hours ago, hyp said:

I think a 2000lm light won’t have enough output to use with a filter. It barely has enough without one. 

That's a good point, Hyp. But maybe it's enough just to add a little fill in the shadows, especially at moderate depths, if you're not using a red filter, and a wet lens at moderate apertures? And what about a GoPro with a light red filter at moderate depths? Might work...

Then again, they're may be a good reason why L&M doesn't offer filters for the little Sola lights. I wonder if it would be feasible to offer those small lights with a switchable 5600K/30,000K output.

[dreifish 362]

21 hours ago, jplaurel said:

I would love to know this as well. It would give new life to some of my old lights, like the old Sola Video 2000. Given the cost of the Lee filters, though, I was thinking that maybe a good option would be to buy a pair of the "bluewater dome port cover" for $39 each that L&M make for the Sola 15,000. I think those Sola 15,000s are pretty big, so they could probably be jury-rigged to fit her lights. You could even cut them down to size for something like the old Solas. At least with these, the only work would be getting them attached in some way. The light color should be perfect, assuming the Sola 15,000 is 5600K.

Bluewater Dome Port Cover for Sola Video 15,000

This would largely depend on whether the L&M filters are suitable to the purpose, which is no guarantee. Keldan has done a bit of research and testing to come up with their filters, no doubt. I'm not sure other manufacturers have.

For instance, I've bought 4x of these filters from Divepro for my g18s and I must say I was quite dissapointed with the results. It's as if they just picked a cyan color at random. https://www.walmart.com/ip/DIVEPRO-F01B-Ambient-Light-Filter-Blue-for-Underwater-Video-Lights/479099933. Doesn't seem to attenuate the warm wavelength sufficiently. 

[jplaurel 46]

13 minutes ago, dreifish said:

This would largely depend on whether the L&M filters are suitable to the purpose, which is no guarantee. Keldan has done a bit of research and testing to come up with their filters, no doubt. I'm not sure other manufacturers have.

For instance, I've bought 4x of these filters from Divepro for my g18s and I must say I was quite dissapointed with the results. It's as if they just picked a cyan color at random. https://www.walmart.com/ip/DIVEPRO-F01B-Ambient-Light-Filter-Blue-for-Underwater-Video-Lights/479099933. Doesn't seem to attenuate the warm wavelength sufficiently. 

Glad you mentioned that, because I'd run into those filters as well. Well, I guess there's no substitute for actual research into the color science, and at the moment, Keldan seems to be the only company pursuing it for underwater video lights. The AF-12 filters work very well on my Keldan 4x and 8x. I also have the 30,000k cyan heads for my old Luna 8s, which are the same light color.

As an aside, if you use the AF-12B filters, pay attention to the "use in water only" warning. I had to hand my rig off to a fellow diver just before we surfaced, and I neglected to turn the 4x adjustment ring to the lock position. Of course, they got bumped as they were brought up into the RIB, and after 5 minutes, this is what happened. Expensive lesson!

 

Edited May 6, 2022 by jplaurel

[dreifish 362]

24 minutes ago, jplaurel said:

Glad you mentioned that, because I'd run into those filters as well. Well, I guess there's no substitute for actual research into the color science, and at the moment, Keldan seems to be the only company pursuing it for underwater video lights. The AF-12 filters work very well on my Keldan 4x and 8x. I also have the 30,000k cyan heads for my old Luna 8s, which are the same light color.

As an aside, if you use the AF-12B filters, pay attention 

Keldan AF-12B Melted-1.HEICUnavailable Keldan AF-12B Melted-2.HEICUnavailable

Interesting, JP. So are you suggesting that the AF-12B filters from Keldan more or less produce the same light temperature/quality as the old 30k cyan heads? 

If so,  the 200 Double CTB gel from Lee Filters would be a good starting point for experimentation:

200 Double CTB

Converts tungsten (3200K) to daylight (26000K) 

 https://www.leefilters.com/lighting/colour-details.html#200&filter=cf&sort=number

On the topic of light output, 2000 lumens is definitely too weak for use in wide angle, even without the filter. My understanding is that the AF-12B filter knocks down light output by 2 stops, i.e., they lead to around 25% of the same illumination as without a filter. 

In practice, I've tried using Keldan Filters with 2x luna 8s (about 13k lumens each) in the past and didn't feel they produced enough illumination to fill in shadows in typical tropical diving conditions. It doesn't help that the Keldan Luna 8s have a 110 beam angle -- it diffuses the light over too wide an area imo, reducing effective illumination. Part of the reason I went with DivePro g18s (apart from the price!) is the tighter 95 degree beam angle, which leads to almost 2x brightness over the area you're interested in. More on that here: 

 

By my calculations, you really need about 4x ~15k lumen lights to start to get acceptable results with ambient light filters in tropical diving conditions. You can maybe get away with 2x on early morning/late afternoon dives, overcast days or below 30m (but then, you perhaps shouldn't be using this mixed light approach at those depths anyway, IMO. It's most effective down to 20, 25m where it's still possible to recover some warmer colours from ambient light). 

Final point -- yep, definitely be careful, the heat put out by 15k lights that close to the element is deceptive! Don't use them in air if you can avoid it. This is doubly true if working with gels rather than glass filters. I've melted a few in past experiments

 

Edited May 6, 2022 by dreifish

[dreifish 362]

Hmm.. perhaps we can reverse engineer our way to the optical formula Keldan uses in their blue filters . I just did a quick an dirty test shining with a DivePro g18 light at 50% power onto a white wall (painted in Benjimin Moore Chantilly Lace, if you're really curious). I did it first with the bare light, and then with the Divepro Blue Filter to measure the effect. I took photos to gauge exposure and white balance. I've exported both photos here with white balance set to daylight so you can see the difference, but then did a custom white balance off the wall to measure light temperature:

Without Blue Filter:

ISO 200, 1/200, F4.0 @ 14mm, WB: 4800k +15 magenta

With Blue Filter

ISO 200 1/160, F4.0 @ 14mm, WB 7350 +84 magenta

This leads me to conclude that the DivePro blue filter is just not strong enough. On the positive side, it only reduces light output by ~1/3 of a stop. But it also only cools the color temperature down by ~2500k. 

Could someone with access to the Keldan blue filters or the Light & Motion ones perform the same test for comparison?

 

 

Edited May 7, 2022 by dreifish

[shanesmith.photos 13]

Really interesting info, thanks @jplaurel! You mentioned that you were getting quite a bit of noise in the final video. What aperture and ISO ranges did you take most of the video at? I've just got myself a rig very similar to this but haven't had a chance to do any video with it yet, so I'm really curious about what one can get away with behind the WWL-1 for video.

[dlwheeler05 0]

@dreifishI have 2 Gates GT14 video lights and would like to use filters for ambient light. Which filter did you use for blue water for depth range of about 10-18 meters? I would like something comparable to the Keldan filters. Ambient Filter AF 12 Blue Water

I was looking at filters here: 58 mm color filters | B&H Photo Video
 

thanks.

[jplaurel 46]

23 hours ago, dlwheeler05 said:

@dreifishI have 2 Gates GT14 video lights and would like to use filters for ambient light. Which filter did you use for blue water for depth range of about 10-18 meters? I would like something comparable to the Keldan filters. Ambient Filter AF 12 Blue Water

I was looking at filters here: 58 mm color filters | B&H Photo Video
 

thanks.

I use the Keldan SF-2 spectrum filter (for the camera) and the Keldan AF-12B for the lights. Assuming your Gates lights output at 5600K, then the Keldan AF-12B should work, assuming you can find a way to fit them. The inside diameter of these filters is 72mm. They also make a larger version that is 110mm. Daniel Keller mentioned that they can supply the AF-12B material by itself. So, you could get some of that material, a few 58mm filter rings, and make some 58mm filters for your Gates lights with the Gates filter mount. I do see from the specs that the Gates lights are 5000K. Keldan are very responsive. You can reach them here: https://keldanlights.com/contact/contact.html

 

Edited May 12, 2022 by jplaurel

[dreifish 362]

On 5/11/2022 at 11:29 PM, jplaurel said:

I use the Keldan SF-2 spectrum filter (for the camera) and the Keldan AF-12B for the lights. Assuming your Gates lights output at 5600K, then the Keldan AF-12B should work, assuming you can find a way to fit them. The inside diameter of these filters is 72mm. They also make a larger version that is 110mm. Daniel Keller mentioned that they can supply the AF-12B material by itself. So, you could get some of that material, a few 58mm filter rings, and make some 58mm filters for your Gates lights with the Gates filter mount. I do see from the specs that the Gates lights are 5000K. Keldan are very responsive. You can reach them here: https://keldanlights.com/contact/contact.html

 

Great! If Keldan sell the AF-12B filter glass stand-alone, perhaps we could fashion comparable filters for other lights. I'll see if they can provide some with a 72mm diameter (DIVEPRO G18s) or 58mm diameter (Gates G14s).

[Davide DB 484]

Guys I'm not sure I followed you on everything...

Where I can find a definitive guide to how to use these filters?

I'm not meaning an explanation of how a car works but an explanation how to use a car: open the door, turn the key.... :)

[lutfu 118]

7 hours ago, Davide DB said:

Guys I'm not sure I followed you on everything...

Where I can find a definitive guide to how to use these filters?

I'm not meaning an explanation of how a car works but an explanation how to use a car: open the door, turn the key....

 

[dreifish 362]

Davide, you could start by watching this video from Florian Fischer: https://www.facebook.com/keldanlights/videos/359120794910357/

How I do it:

1. With the blue filters, the color spectrum output by the video lights more or less matches the color spectrum of the ambient light at a certain depth. What that exact depth is will vary from location to location based on water clarity, time of day, cloudy/not cloudy, etc. But it will usually be somewhere in the 6-12m depth range.

2. I go down to 12 meters and do a MWB off a grey or white card using just ambient light. If the camera can't execute a good MWB at that depth without a red filter, then I use a red filter. 

3. I then lock in that MWB and turn on the video lights with the blue filters in place. There should be no/very minimal color cast to the areas of the scene that the video lights illuminate.

4. I keep the same MWB for any shots at 8m depth or deeper, down to maybe 30m. 

5. Below 30m, I just remove the blue filters from the lights and set a CWB on the camera to 5000k (the color temperature of the video lights). 

5. If I need to shoot above 8m depth, I do a MWB again at that depth based on ambient light alone. I mostly shoot with just ambient light at 8m or shallower. You could try to fill in shadows with your lights, but to avoid red color casts on foreground objects, you'll either need a 2nd set of weaker blue filters that are formulated to match ambient light at shallower depths or you'll need to use your lights at a weaker setting so the red wavelengths they put out aren't so overpowering.

[Davide DB 484]

Thank you all guys,

I would be very curious to test it in Mediterranean waters. Unfortunately (or fortunately for my pocket) my Luna 8 CRI lightheads are not compatible. Maybe with some custom gel but they are definitely too weak.

Shallow shots with this technique are on another league.

[lutfu 118]

12 hours ago, Davide DB said:

Thank you all guys,

I would be very curious to test it in Mediterranean waters. Unfortunately (or fortunately for my pocket) my Luna 8 CRI lightheads are not compatible. Maybe with some custom gel but they are definitely too weak.

Shallow shots with this technique are on another league.

Once i did this with a ur pro red filter and scubalamp ambient filters in front of scualamp 6vk lights, mediterranean sea 

the fish are 5 meters and the wreck is about 21 meters

[lutfu 118]

10 meters and Half meter but im not sure if i used the filters last one

[Davide DB 484]

Thanks Lutfu!

[rgilkes 11]

Just got in ambient filters for the Sola Pro 15Ks. Will be testing this week. 

[dreifish 362]

Please take some photos with the bare light and with the light + blue filter to measure the color temperature (mired shift)

[dreifish 362]

My Lee Half CTB, Full CTB and 2 CTB filters have arrived, along with a whole swatch of Rosco filters. So I did some more testing with interesting results:

1. The LEE CTB filters aren't as good as I hoped. They increase the color temperture (I.e. introduce a lot of blue) but don't introduce enough green into the light to match underwater ambient light. Results:

• No Filter = 4750K, +14 Magenta, 0 stops light lost
• Half CTB = 7550K, +6 Magenta, 2/3 stops light lost
• Full CTB = 21000K, +7 Magenta, 1 1/3 stops light lost
• 2x Full CTB = 50000K +12 Magenta, 2 stops light lost (in fact, 50000K was not sufficient to restore neutral color -- I had to dial down blue saturation to -100 in Lightroom)

2. From the Rosco filters, I tried the Cyan 30 (#4330), Cyan 60 (#4360), Cyan 90 (#4390) and Storaro Cyan (#2005). Interstingly, the Cyan 30 perfectly matched the DivePro F01C filter. I'm guessing this would be good at around 3-5m depth to match ambient light?

• No Filter = 4750K, +14 Magenta, 0 stops light lost
• Cyan 30/DivePro F01C = 6600k , +67 Magenta, 1/3 stops light lost
• Cyan 60 = 8600k, +116 Magneta, 2/3 stops light lost
• Cyan 90 = 12250K, +150 Magneta, 1 1/3 stops light lost
• Storaro Cyan = 13250K, +150 Magneta, 2 stops light lost (in fact, +150 magneta was not sufficient to restore neutral color. I had to dial down Aqua saturation -100 and Orange saturation -100 in Lightroom to get rid of the remaining color cast)

 

Based on above testing, I think the Cyan 60 might be a pretty good start for matching ambient light at 6-9 meters. Cyan 90 for 9-12 meters. Not really worth using the Storaro Cyan or the 2x Full CTB.

Next up -- testing combinations of Cyan 60/90 + Half CTB/Full CTB. Cyan 60 +  Half CTB should create interesting results.

Looks like @Interceptor121 did some testing with Cyan 60 gels on his strobes a few years back with good results: https://interceptor121.com/2019/09/29/creative-strobe-filters-for-wide-angle/. He also did some testing with custom filters for his DivePro lights in 2019 with nice results at 9 meters depth. Results at 18m don't look so great in my view. But he doesn't specify which filter he used on the lights.