June 26, 2015 at 1:09AM

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CTO gel for windows: Why not get ND filtering as well?

Hi all.

I'll be shooting indoors where there are large windows and lots of daylight coming in, and actors will be moving about in front of them in many shots. I have only a minimal lighting kit, all relatively low-powered halogen bulbs.

Because I can't overpower the daylight with daylight-colored lights, I need to gel the windows. I'm thinking that CTO with .9 ND is the way to go. Can anybody weigh in on this? It seems to me that three stops isn't too many, and if it is, I can reduce the amount of artificial light.

Thanks for any advice.

12 Comments

Three stops of ND should be fine. Daylight is very bright, so you will need the ND to give your tungsten lights a fighting chance against the window light.

June 26, 2015 at 3:16AM

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Guy McLoughlin
Video Producer
31440

Thanks, Guy. That's the highest ND I can find in a CTO anyway.

David Gurney

June 26, 2015 at 4:45PM

If my memory is correct full CTO eats up 2/3 F-stop, so you really are reducing the light through the windows by 3.66 F-stops.

June 26, 2015 at 5:14PM

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Guy McLoughlin
Video Producer
31440

You mention "large windows". How much gel will you need? Gel is not cheap, and this is also time-consuming work. Have you considered that it might be more efficient and even maybe cheaper to rent some HMI's?

June 26, 2015 at 7:00PM

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Gerrit Haaland
Filmmaker
83

.9 ND seems the way to go for day. I definitely wouldn't put CTO on the windows though why would a source through a window have the same colour temp as tungsten? Also just because you have ND on the windows doesn't mean the light variation through that window will stop. If the sun breaks through the clouds mid shot you are in trouble as you would then have to match that for close-up/reverse. Playing with the sun indoors in a long scene is dangerous as the sun moves throughout the day, the ND helps but you're still going to get a variation of light through the windows depending on how hard the light is. An overcast day would be exactly what you need, get someone to do weather cover and have them look (safely, ie with a pan glass) at the sun and rely the information to you as how long you have cloud for or how long the sun will be out for. If you establish in the shot that the windows are there do not put CTO on them it needs to be of daylight colour temperature. Have practical in shot lamps inside then use your small tungsten to replicate those, there is nothing wrong with mixing sources with diff colour temperatures in a shot. What you could do if you think the mix of tungsten and daylight is too ugh is blue your tungsten slightly like adding 1/4 or 1/2 CTB to the tungsten heads (not the pracs in shot obviously) that will still give you a contast between your daylight and artificial sources but not too much. What you would ideally do with the sun is flag it out and then move that flag throughout the day, due to the sun moving, however you need the really big weapons for that.

June 27, 2015 at 5:53AM

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Gino Lynch
filmmaker
134

>>>I definitely wouldn't put CTO on the windows though why would a source through a window have the same colour temp as tungsten?

If he's using tungsten lights to light his interior and does not want the outside to look blue, or the inside to look orange, then he needs to achieve one color balance for everything to look neutral. In this case it will be a tungsten color balance, and everything will look neutral color, both the inside set and the outside through the windows.

June 27, 2015 at 10:31AM

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Guy McLoughlin
Video Producer
31440

Sorry Guy but if you establish there is windows in a scene that source is daylight nothing else, simple as that. If you gel that source with CTO what are those windows suppossed to replicate? Two huge tungsten sources? No. If he is shooting where daylight is coming through a window and he has tungsten sources from inside (visable in shot i.e bedside lamp/house lights a fridge opening) there MUST be a contrast as they are two different sources/types of light. If he doesn't want a mix then he should use one or the other. If he just wants tungsten then he should blackout the windows entirely, but if it's day you would imagine there would a daylight ambient. I did suggest adding 1/4 CTB to the tungsten heads to give the light a bit more of a balance but maintain a contrast between the two sources. Putting CTO on the windows will give a tungsten ambient. The outside is blue, the colour temp of the sun only changes slightly at dusk or dawn. Another option would be to gel the tungsten lamps blue and use them in a way that the they are replicating an overall ambient from the windows i.e bounced off the floor/walls, that would mean there should be no practical lamps on in shot. It all depends on what you want your tungsten lamps to replicate. If there is prac lamps on in shot there need to a contrast established between the big man in the sky and your standard household lighting. If you persist on geling the windows CTO then do not balance your camera to tungsten, you need to rebalance your camera on the kelvin scale to make (through the view of the camera) the source coming through the window/overall ambient look like daylight.

This is all presuming your scene is set during the day. If the scene is set at night then that is a different kettle of fish.

June 27, 2015 at 3:00PM, Edited June 27, 3:07PM

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Gino Lynch
filmmaker
134

>>>Sorry Guy but if you establish there is windows in a scene that source is daylight nothing else, simple as that.

During a "day" scene the viewer automatically assumes that any light coming through a window is daylight, but technically they really have no idea what color temperature of the light coming through the window was when the shoot took place.

Using CTO and ND filters to balance window light with interior tungsten lights is a very old and common technique that has been used for many decades. As long as the light coming through the windows looks "neutral" in the finished image, is does not matter how this was achieved.

The last thing you want to see in your film is blue highlights from the window light with neutral shadows from the interior tungsten lights, or neutral highlights from the window light with orange shadows from the interior tungsten lights. It's fine if it's subtle and done as an effect in the finished film, but you have to start from a "neutral" color balance and then decide where you want to go from there.

June 27, 2015 at 4:35PM, Edited June 27, 4:36PM

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Guy McLoughlin
Video Producer
31440

My point is if you put CTO on the windows you will have big sources of light coming through a window that does not look like daylight, I'm not saying the audience will sit there and say 'oh that colour temperature isn't right' however it will look strange and won't look right and the audience will identify that. David stated that he will have actors play out action in front of the windows therefore you cannot cheat that source in using it as a tungsten ambient. Lighting is replicating the sources you establish in a scene, if you shoot a scene to establish daytime with big windows your primary source is going to be daylight not tungsten so why would you gel the windows with CTO? Honestly it just wouldn't look right. I've worked as film spark for years and mixing tungsten and daylight sources works because it makes sense in certain situations, I've never once gelled windows with CTO for a daytime scene, I'm not saying it should never be done but there must be a logical reason for it, lighting most of the time is simple; replicate the lighting sources you establish, if you establish there is windows in a scene thats's daylight, simple. Changing that source to tungsten has no logic, either does the concept you put forward of neutral balance. If you have a mix of tungsten and daylight sources you balance the camera accordingly, there will be a contrast in the image but so there should be. Life brings up scenarios where Colour temperature of light is mixed all the time due to a mix of sources and thus film does so as well to replicate that and it's important on those occassions to show a contrast in colour. Im currently working on a film at the minute with a pretty hefty budget we are working with talented DP and we are constantly mixing lamps of different colour temps when the situation is right. Sometimes we only use tungsten; sometimes we only use daylight; and sometimes there's a mix of both. If you have tungsten as the main source you could colour correct in post but to me the 'we'll fix it post' mentality is a destructive one.

June 28, 2015 at 1:48AM

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Gino Lynch
filmmaker
134

Please ignore my ranting about the CTO on the windows David. I've done a bit of research and yes it is a viable solution, I look like quite a knob now lol. I've just never come across it before I'd be used to using big 5600k HMIs through windows, the CTO solution is a simple one and yesterday my brain didn't compute that information relative to the balance of the camera. Also we light with big tungsten through windows in studio film and TV so why that concept didn't click with me is pretty embarrassing. Apologises Guy but you were right about that. I'd like to think the rest of the info I posted was correct.

June 28, 2015 at 6:45PM

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Gino Lynch
filmmaker
134

You will almost never see productions gelling windows (at least not more than one or two). It's rarely worth the hassle and leaves you having to deal with potential light flickers from the gel moving with the wind, gel falling off, gel making noise when caught in the wind and not to mention the time it takes to put them up.

Alternatives (aside from using daylight temperatured fixtures) include shooting during dusk or dawn (golden hour) when the sun isn't as strong, or choosing a location that doesn't have direct sunlight entering through the windows. I once lit a conference room by hanging a 2x8 silk along the wall opposite the windows.

Nowadays though I have learned to love the look of blown out windows (controlled) and not be bothered by having my scene lit entirely through natural window light. If you got lenses fast enough, just turn off your tungsten practicals and use negative fill to shape what you get from the windows. It'll save you a lot of hair and stress wrinkles, trust me.

June 28, 2015 at 7:10PM

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Tobias N
Director of Photography
1318

>>>You will almost never see productions gelling windows (at least not more than one or two)

I think this is because we have lots of daylight light sources to light interiors now ( HMI, Fluorescents, LED, Remote Phosphor, etc... ), so it's easy to match the color balance and possible to match the brightness with certain light sources.

When I shoot corporate interviews, I try and work with the windows in the room and balance things out with 1x1 daylight LED lights. ( I also own a couple of fluorescent Diva lights, but these are a pain to transport compared to the LED lights )

Remote Phosphor looks like it might be the future of cine lighting if they can get the power up enough. ( certainly it's bright enough for small sets right now )

June 29, 2015 at 5:51PM

6
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Guy McLoughlin
Video Producer
31440

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