Videomaker – Learn video production and editing, camera reviews › Forums › General › Using Gels – article in magazine, but I disagree with so much of what it says!
April 26, 2019 at 1:17 AM #72014164paulearsParticipant
I read with interest the article in the magazine I read online today.
“Lighting gels serve a number of purposes, but the ultimate goal of any gel is to change a light’s color temperature.”
Absolutely and utterly wrong!! They change the colour. They could change the colour temperature, as in the CTO, CTB gels talked about a bit later, but once you move from these few gels to the colours, then what they really do is take bites out of the rainbow spectrum that tries to pass through them. If you take out the green and blue, you get left with the red content. If you look at the hundreds of gels in a swatch book, you’ll see a graph showing where they work. You get great weird ones too – Lee 126, Mauve – it appears to be a very dark purple – but anything yellow in the image, like a banana turns red! If you stick a bit over the lens of your camera it can be very odd, and practically impossible to create as a colour tweak in the edit. Gel changes colour. It does it by subtraction, so it’s wasteful of light. Some dark blue gel – Congo 181 for instance, is so dark it lets less than 1% of the light through – the rest goes up in heat!
Gels are designed for tungsten light sources, 3K or 3.2K. The manufacturers have produced a totally different range of gels for LED sources that give the same colour on the subject from white LED light. A piece of tungsten gel and the identical colour effect LED gel look totally different to the naked eye, holding them up to a light source. This is of course because light from a heated piece of metal filament has gentle peaks and troughs in the frequency response, while LEDs have very sharp and powerful spikes, with very large missing sections.
If you make music videos, then gels have been your friend for years, now, far less so. I’m personally down to very few tungsten sources, and I’m saving hundreds a year in melted and faded bits of plastic film. I still buy CT gel- but be aware again that converting lights from colour to colour is more difficult that it appears. My own rule is to recolour the brightest light source. Trying to blue up a tungsten source to match daylight is often ineffective. After 93 million miles, the sun is still so bright even a 2K tungsten source hardly makes an impact. If the light from the sun comes through a window, then you can put CTO on the window and tint the sunlight an orange colour which lowers the apparent colour temperature of the sun. The light stays at 3 or 3.2K and you tell the camera that and all is well. If you have inside lighting and mix tungsten and discharge, then colour treat the HMI. If your brightest source is say a 1.2K Arri, but your other lights are LED panels, then CTB on the Arri may make it closer to the LED light, but many LEDs have varieties of white, so looking through t he camera carefully is important.
“Gels alleviate this spill by keeping the light intensity down — a cheaper alternative to reflective panels and umbrellas.”
Rubbish! I’ve no idea what the writer meant here. If you get spill from your green screen, then that is light landing on the subject that you don’t want – black wrap or light sources with barn doors or just better fixture focussing is the key here – dimming them to lower spill lowers the light you want. If you use a colour filter, light drops, but what colour? A gel that cuts green would work, so a magenta gel allows little green light through, but that would be ineffective landing on a green surface? Reflective panels and umbrellas soften light – what has that to do with colour? Towards the end, the writer starts to talk about changing colours for mood, which is of course their primary role. Colour and Colour correction are VERY different uses, and the article in the first section really confuses new readers.
The article is essentially correct, but presented in a style that makes big statements that will confuse, then corrects them later.
My first experience with gels was in the 70s and the damn things were fragile, short lasting as they faded quickly and expensive, I still have rolls and rolls in the store, and out of hundreds of colours available – colour correction is a very small number – a few blues, a few oranges, and then the ones to remove flu tube casts. The vast number are for colours – NOT colour temperatures. The best selling ones are NOT CT.
April 30, 2019 at 10:12 AM #72014475JackWolcottParticipant
Great comment Paul. As one who has worked with stage lighting for more than 50 years I concur completely. Physically, gels have come a long way from the 1970, of course, with plastics and composite media, but color still works the same way.
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