Gelling HMI to balance with tungsten?

[Ron Michaels]

Which gels should I be looking for? I know ROSCO has a gel called "HMI to TUNGSTEN" but it looks as if it is meant for 5000k lights, not 5500 to 6000. There is also an assortment of others that seem to be a mix and match kinda thing. Anyone have any experience or input with this?
thanks again,
Ron

 

[Josiah Duncan]

Just use anything that's labeled as a Full stop of CTO. Actual daylight varies by a couple hundred kelvin throughout the day, I would start with a full stop and add or subtract in 1/8ths from there. It's likely the HMI>Tungsten gel is pretty much also a full stop CTO. The actual color temp of the bulb also varies throughout it's life cycle anyway, but I think you would be challenged the tell the difference.

 

[Ron Michaels]

Tried a CTO that gave a pretty strong magenta hue. Didn't match the tungsten light at all in terms of tint. It was a standard CTO from ROSCO, brand new. The HMI lamp I tried it on is rated 90 CRI at 6000k but measures normal daylight 5600.

 

[Maz Mawlawi]

CTO only balances out the color temperature and NOT the tint....you may have to apply some gels like a minus or plus green etc... to get the correct color to match Tungsten. Like Josiah said the color of the bulb varies throughout it's cycle. Using a spectrometer would help you determine the correct combination of gels.

 

[Jake Wilganowski]

Yep just use different strengths of plus green to get where you want

 

[Robert Hart]

POSSIBLY RELEVENT LEE FILTER NUMBERS -


PURPOSED FOR FILTERING THE NEAR-DAYLIGHT OF HMI TO MATCH TUNGSTEN LIGHTING.

236 HMI TO TUNGSTEN


PURPOSED FOR PARTIAL ELIMINATION OF GREEN CAST FROM FLUORESCENT LIGHTING

279 EIGHTH MINUS GREEN

 

[David W. Jones]

This is where having access to a color temp meter is worth it's weight in gold.

Lamps change color temp as they age. Using a color temp meter gets you on the money very quickly.

 

[Noah Yuan-Vogel]

Yeah that's the problem with using gels to change color temp of a light source with a spikey spectral output. The CTO will lower the output of light in the blue part of the spectrum but leave the green spike mostly intact so the green spike will be amplified relative to the resulting output (the output is actually lowered but the green output remains the same).

 

[Ron Michaels]

CTO's and CTS's combined with either plus green and/or minus green are giving me some ugly color! Gonna try the gels specifically made for hmi to tungsten from lee and rosco. We'll see if they are any better....so far the CT gels don't look to good.

 

[abreu-canedo]

Do a scene test with your fixtures. Then bring in the footage and color correct it using blue/yellow and green/magenta adjustments in post until you get the result you want. Then you can reverse engineer your adjustments in post to their equivalent units in gels. But having a spectral read-out of the light coming from your fixtures is really useful, so you can know exactly what it's doing across the entire spectrum of visible wavelengths...which may not always translate exactly in software adjustments.

 

[Marc Wielage]

Do a scene test with your fixtures. Then bring in the footage and color correct it using blue/yellow and green/magenta adjustments in post until you get the result you want. Then you can reverse engineer your adjustments in post to their equivalent units in gels.

Be warned that often, the resultant white balance in post can look very odd and "dirty," with a lot of weird artifacts. This is a typical problem of mixed lighting, particularly issues with tungsten lighting.

 

[Hrvoje Simic]

Do a scene test with your fixtures. Then bring in the footage and color correct it using blue/yellow and green/magenta adjustments in post until you get the result you want. adjustments

That is a rudimentary adjustment and doesn't compensate particular spectral offsets.


I suggest taking these words very seriously and avoid mixed artificial light sources when possible:

Be warned that often, the resultant white balance in post can look very odd and "dirty," with a lot of weird artifacts. This is a typical problem of mixed lighting,

 

[Glen David Miller]

Would this be the time to tell the story of the famous film shot a while ago with a famous British DP who never really bothered to worry about the correct balance of Negative loaded into the camera. Didn't care. And in the end, you would never know.

 

[abreu-canedo]

Be warned that often, the resultant white balance in post can look very odd and "dirty," with a lot of weird artifacts. This is a typical problem of mixed lighting, particularly issues with tungsten lighting.

Right. My suggestion was not to "fix it in post", but to use post software to give you an idea of which fixtures need what type of gels based on the adjustments you make in post. So, you'd essentially reverse engineer your post adjustments into their equivalent units in gels on set.

Means I also mentioned to be careful and get a spectral reading of the lights because the process I mentioned may not fully account for non-continuous wavelength spectrum or odd spikes as clearly.

So so I don't necessarily disagree. Just perhaps I didn't make myself clear? Or am I misunderstanding you?

 

[Ron Michaels]

Hey guys, new question. I've found using rosco UV gels seems to add more green to my HMI, enough to where it needs correction. Are these gels really necessary nowadays being as how the bulbs are UV protected?
thanks,
Ron

 

[Ron Michaels]

Be warned that often, the resultant white balance in post can look very odd and "dirty," with a lot of weird artifacts. This is a typical problem of mixed lighting, particularly issues with tungsten lighting.

im assuming you mean balancing mixed lighting to 3200 and not balancing tungsten to match daylight fixtures such as flo's and HMI's? Or both?
thanks,
Ron

 

[abreu-canedo]

Most digital sensors are balanced for daylight capture...so around 5600k. Doing in camera white balance to 3200k simply amplifies the blue and green channels, which can introduce noise. In some case, if combined with ISO adjustments, it can even clip the blue and green channels. Of course, this is less of an issue when shooting raw. However, when shooting tungsten, there is such little blue wavelengths that the sensor can be starved of blue, thus also contributing to noise in said channel. Specially since blue wavelengths are much smaller and faster, so digital sensors already have a harder time collecting blues. The warmer wavelengths are deeper and slower so the penetrate the photosite troughs much more easily. For this reason, I generally recommend lighting a scene for capture at around 5600k.

Of course, light temperatures is a creative decision. I often mix lights for emotional effect, but I do it knowing that I won't be white balancing for it. So my tungsten look usually means warmer lights at around 4000-4500k, just to separate them from the 5600k lights in a scene. This still provides enough info to all color channels, then if I need them to be warmer, I can push them further in post, knowing that I have enough information in all color channels to maintain fidelity and fine textures in the image.

This also holds true when working with saturated lights, colored stage lights or disco LEDs. When going for an extreme saturated look such as in a club, or a dark-room, I prefer to not go fully saturated on set in any given color. If a lit scene needs to read as red, for example, I'll still make sure their is some white light in that red light (so not fully saturated) so that the other color channels also capture information. Then I can push that red saturation in post and still retain fine textures and more fidelity. Otherwise, if you go fully saturated on set, you starve the other color channels and you have less information to work with.

Of course, this is not a rule, just one practice that I find helpful.

 

[Marc Wielage]

Would this be the time to tell the story of the famous film shot a while ago with a famous British DP who never really bothered to worry about the correct balance of Negative loaded into the camera. Didn't care. And in the end, you would never know.

I'm not sure what you mean by "correct balance of negative loaded in the camera." But if you mean mixed lighting...

As long as they didn't want clean whites and accurate color, and they liked that look, they can use any lights they want. I can assure you it is hard to balance a scene in post that is shot with a variety of different color temperatures. I've done it, the shows have aired and been shown in theaters, but it's an exhausting and miserable experience. The end results are a lot more pleasing when the scene is well-planned and controlled in terms of color temperature and exposure. It also takes a lot less time in post, and I think accurate whites and blacks are one of the building blocks for color in post.

If they want small pockets of yellow light here and there in the background, that's fine as long as that's what you want. But the potential for disaster is pretty great these days, particularly when DPs can use LEDs, HMIs, incandescents, fluorescents, daylight, and a combination of all or some of them, up to and including open flames. Combine that with the risk of overloading IR and other issues... it's not as simple or easy as you might think.

 

[Mihnea Bi]

IF full CTO is too magenta, then full CTS should work... After that I dont think you will need extra plus green.