How do you know when to use 1/8, 1/4, 1/2 or full CTO?

I'm beginning to understand the use of gels for balancing flash and ambient light outdoors. I also know that I love the look of having my man light warmed up a bit and would like to do that with a gel as it's being shot. I don't want a warming filter on the lens because I typically don't like the whole shot with the filter but find it to be very pleasing on skin tones. This would also save me a step in post processing where I add a warming filter.

Is it more trial and error to determine which CTO gel is going to work the best or is there a science to it?

TMR Design wrote in post #5721585
Is it more trial and error to determine which CTO gel is going to work the best or is there a science to it?

I am not an authority on this but I offer my experience.

Like you I use gels for artistic purposes from time to time. If I am photographing a staged scene I just use the colors I want and that is based on ART not science...

But your question I assume is in areas outside your studio and areas you don't have total control over. You and I need to buy this:

Sekonic Prodigi Color C-500 Color Meter

Most of the time doing weddings and the like I don't gel. As I walk from room to room it is to hard to get exact because of flash angle and bounced heights. You can only get close... The only time I would gel in these scenarios is when my flash lights the room I am in but not the room behind the subject lite with tungsten. In those scenarios just put a CTO 1/4 and it will be close.

Thanks man,

I should have specified that this is only when I'm doing portraiture.

TMR Design wrote in post #5721653
I should have specified that this is only when I'm doing portraiture.

One note I will add. There is a recent thread in which someone thought I should have used a CTO gel to balance a scene. However the resultant shot I took was because I was bouncing off of a certain color wood not because tungsten bulbs where in use (they where but my flash was over powering them).

When I am doing event photography I don't get paid to case the venue like a full production movie crew would do. Yes I should have color tested what the wood would do to the subjects. I just don't get paid to do that...

TMR Design wrote in post #5721653
Thanks man,

I should have specified that this is only when I'm doing portraiture.

I kinda think CTO gels are a bit too orangey/redy for shooting people and have always preferred these rosco gels:

Cinegel #3444: Eighth Straw 1/8 CTS
Cinegel #3443: Quarter Straw 1/4 CTS

However, I love CTOs for non-human subjects...especially food shots and architectural interiors. Generally, I'll use a full CTO for those kinds of subjects....it's much more fun to go all the way when warming up a strobe rather than going halfway or 1/8th of the way

Just an opinion...I'm sure others will certainly disagree

Gentleman Villain wrote in post #5721681
I kinda think CTO gels are a bit too orangey/redy for shooting people and have always preferred these rosco gels:

Cinegel #3444: Eighth Straw 1/8 CTS
Cinegel #3443: Quarter Straw 1/4 CTS

However, I love CTOs for non-human subjects...especially food shots and architectural interiors. Generally, I'll use a full CTO for those kinds of subjects....it's much more fun to go all the way when warming up a strobe rather than going halfway or 1/8th of the way

Just an opinion...I'm sure others will certainly disagree

Interesting. Thank you. I'm going to have to play around with the Rosco swatches to get a feel for the differences in these gels.

I posted on the subject a little while ago on this thread:

https://photography-on-the.net/forum/showthre​ad.php?t=518707

Essentially it is a combination of experience and trial & error. There is little point spending money on a colour meter as you will generally only be choosing between three gels, 1/4, 1/2 and full CTO - with a little bit of practice, making the choice will be second nature.

As has been mentioned, CT Straw is also useful on occasion although personally I prefer to reduce the amount of CTO on the flash when shooting people rather than switching to straw, as it does give a yellow cast which does not suit everybody.

TMR Design wrote in post #5721585
I'm beginning to understand the use of gels for balancing flash and ambient light outdoors. I also know that I love the look of having my man light warmed up a bit and would like to do that with a gel as it's being shot. I don't want a warming filter on the lens because I typically don't like the whole shot with the filter but find it to be very pleasing on skin tones. This would also save me a step in post processing where I add a warming filter.

Is it more trial and error to determine which CTO gel is going to work the best or is there a science to it?

There is a science to the light shifting of gels. However, I do not know how to apply it....selectively...th​e way you want to. It is much easier to apply it to a masked layer in Photoshop.

Thank you for the suggestions guys.

I just did some testing, and although this won't help me in terms of balancing flash with ambient light, it does show me the warming effect on skin tones (well, fake skin, that is).

I shot these samples using a Nikon SB-800 at a constant f/9. Custom white balance was set for the first shot with no gel. Some color is lost in the web optimized images but you can still see the effect. There is a slight difference between CTO and CTS and can really only be seen with a larger, higher resolution image.

I didn't check color temperature to see how much the temperature shifted with each one. This was just done as a visual test but I can definitely say that either the 1/8 CTO or 1/8 CTS are exactly what I was looking for and almost identical to the warming I would add with a layer mask in Photoshop. I'd much prefer to get it in camera so I think that I'm going to try the 1/8 CTO on my next shoot. The 1/4 and 1/2 are just too extreme, or at least it seems that way. I can see trying 1/4 but 1/2 or greater seems a bit much.

In my shots I'm obviously close enough to the background to see the effect but if I were shooting outside and my background was a natural setting with ambient light then I suspect the gel'ed light wouldn't have any effect on the ambient surroundings.

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TMR Design wrote in post #5723063
I just did some testing...

I had my fingers crossed you would do this! I have enjoyed your other posts with this model...

The reason you might use a 1/4 is when the subject has a good deal of naturally occurring (or light bulbs) of CTO on them already. Your test show that it might be unpleasant to create it by itself.

Hi pcunite,

Thanks for that tip. I guess I'll find out where I stand once I start experimenting with real subject's outside.

TMR Design wrote in post #5721585
I also know that I love the look of having my man light warmed up a bit and would like to do that with a gel as it's being shot.

I love to have my man light warmed up in the evenings, around sunset.


Here I used a Roscosun 1/2 CTO. The effect isn't too bad, but to me it is a bit strong (not mentioning the underexposure and other stuff, but its the only example I have). A 1/4 or 1/8 might have been better in this situation. This was very near sunset. It is also just a half-candid with my sister-in-law and her husband. They actually like it, but they are very pale/reddish to start with.

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TMR Design wrote in post #5723063
I just did some testing, and although this won't help me in terms of balancing flash with ambient light, it does show me the warming effect on skin tones (well, fake skin, that is).

I see that she's had another hair makeover, Robert.

For outdoor portraiture, I think in practical terms the best procedure is to try to get reasonably close with the gel, shoot a white balance target so you can adjust in post to get the subject color correct, and the let the background fall where it may.

I have been known to use a 1/4 CTO in the sunshine to give my subjects a little warmth. As the sun starts to set, I think it's a matter of experience to know when to switch to 1/2 or full CTO (and I certainly don't claim to be good at it).

Artistic intent is a big part of it, too. You can use a CTO gel on your subject and then adjust the color temp accordingly, and it will make a dull sky more blue.

The ratio of flash to ambient plays a role. The color temp of the ambient is important to consider. It's all a crapshoot in some ways and falls into the perfect white balance or pleasing color thing. And color meters, even the best ones were a bit shaky IMO.