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Approach to using Gels

SteveytzSteveytz Member
edited March 2011 in flash & lighting
I've just finished reading on-camera flash and I have a question on the approach to using gels. I understand the reasoning but 1/2 CTS, CTS, CTO? Is it trial and error, or a complicated algorithm?


  • The choice of (1/2 CTS, CTS) or CTO is a personal one.

    CTO tends to give people a warmer color (i.e. slightly reddish/orange) than (1/2 CTS, CTS). Neil has leaned more towards 1/2 CTS or CTS gels.

    From Neil's blog:

    "The Full CTS will bring your flash WB down to around 2900K, more or less neutralising the look of the Tungsten light. The 1/2 CTS will bring your flash WB to around 3800K, which will leave your backgrounds still with a touch of the warmth of Tungsten lighting."

    For my own case, I chose CTS. My camera's tungsten setting is calibrated to 2900K and I often want to neutralize the tungsten light entirely.

  • It does't have to be complicated at all. As mentioned CTO tends to produce slightly more orange in skin tones, I personally use CTS only as I like the skin tones it produces. I have 1/2 and full CTS gels and usually use 1/2 when I want to balance my flash to late afternoon (warm) sun or tungsten light indoors. By using 1/2 CTS and not fully balancing to the background tungsten it leaves a slightly warm glow to the background which I like. If the ambient is really warm then I might go to full CTS, but if there is a mix of cooler daylight and just a little tungsten in the ambient I usually don't gel the flash at all, the LCD can really help in determining what your balance looks like here but I find I just get a feel for the ambient light and gel accordingly.

    Flourescent of course is a different story and requires different gels but there seems to be so many different ones around these days that it can be difficult to gel for. I usually just use available light or overpower the available with flash. If possible I turn any flouros off, leave on tungsten lights and any available light.

    I have to say that gelling your flash to closer match the available light can make a huge difference to the look of your images and save you lots of time in post trying to colour correct when you have multiple temps. present, so it's definately worth experimenting with, you don't need to be exact to make significant improvements. I have seen a picture where the photographer used some material from the lining of his coat pocket which was orange, to 'gel' his flash because the room light was so warm and he didn't have any gels at hand, the results were very good. Also keep in mind that if you bounce the flash it can pick up the colour of the surface you are bouncing on, so you might not need to gel if bouncing off a warm coloured walll or a gold reflector.

    Hope you don't mind the long reply, good luck.
  • Thanks for the insight. I have just bought a life time supply of CTS and 1/2CTS, and I'm already enjoying the results. I'm going to experiment with different senarios so hopefully I'll be ready when it counts.
    Thanks again.
  • Neil vNNeil vN Administrator
    Steve ... I do think you'll like the results.

    It's partly trial & error ..
    but generally,
    if I want to have my flash as neutral as possible, or work in light that is very warm, then I opt for full CTS.
    If I only want to partially gel my flash for tungsten, and get the background still warm, instead of neutral, then I go for 1/2 CTS.

    I mostly just use 1/2 CTS, but keep a strip of full CTS taped to my lens hoods as well.


    I do think that we have a fair amount of leeway as portrait and wedding, and as general photographers ... compared to commercial photographers. For most of us, *any* correction would be better than none. Commercial photographers would be far more particular about specific color balance.
  • When I take my weekly pictures of our Rotary meetings, I have been using 1/2 CTO and setting my D700 WB to 3850K and use RAW. I could balance the image in PS or LR, however it is easier for me to have the "As shot" image close.
    Do any of you more experienced photographers set the WB to match the gel? And is there a chart that gives the Kelvin value of the gels?

  • Please note that the LR and PS do not directly read the WB information from the RAW. They use some other algorithm to determine the WB, so the kelvin rating never seems to match the camera setting, but it looks like what the camera would do.
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