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

Rudi wrote in post #5723333
I see that she's had another hair makeover, Robert.

You know how women are about their vanity Rudi.

Curtis N wrote in post #5725662
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.

Thanks Curtis,

I have a feeling my best bet is going to be having various gels and noting time of day and type of sun and ambient light. Then I can see what works and what doesn't.

A color meter is nice in terms or seeing temperature and shift but doesn't really do much for me with regard to this topic. Either way this is a subjective thing. There is no technically correct way to do it and I think that I'm going to roll the dice and give it a shot

In the samples I shot I used both CTO and CTS gels. They look almost identical in that particular sample.

In general, is one preferred over the other? What is the exact difference between the orange and the straw?

I use a color meter quite a bit, and its very helpful. It would also work well in this situation Robert, since you can measure each light independently or together, and understand the it will have on the subject. Once you get used to reading the light meter, you will know very easily that you have say a 1200K difference between sources. Then you can decide on how you want to correct that.

For example, lets say your ambient lighting was later afternoon sun and it measured at 5150K, while your strobe measured 5500K. Thats a 400K shift between the two. If you used a 1/8 CTO which is a 300K shift, it would correct the 5500K strobe to 5200K, which is still 50K on the cooler side, but barely visibly noticeable. You could also go with a 1/4 CTO and get a warmer light from the strobe on your subject.

Basically, you can take two readings, and know exactly which gel to use without test exposures or guess work. I generally like about a 800K shift on the warmer side for my strobes hitting people to add a warmer skin tone. Generally I can get that on the first shot by measuring and then using the right combination of CTO gels. The same holds true for correcting fluorescents, halogen, tungsten, etc.

The down side is that color meters are expensive. However, it was really necessary when shooting film since visual testing was really a viable option. So learning how to read a meter, and doing the basic math conversions, allowed you to get spot on with the colors. I still do it this way since is so much faster than test exposures. But I find I can usually get right on with known light sources (ie, my strobes are 5200K, bright daylight, etc) and only need to measure when the lighting varies (various stages of sunsets, open shade, different bulb types, etc).

BTW, here are the shift values for CTO
2400K Full CTO
1200K 1/2 CTO
600K 1/4 CTO
300K 1/8CTO

CTB's work in the same way, but shift colors toward the cooler side.

sfaust wrote in post #5726132
I use a color meter quite a bit, and its very helpful. It would also work well in this situation Robert, since you can measure each light independently or together, and understand the it will have on the subject. Once you get used to reading the light meter, you will know very easily that you have say a 1200K difference between sources. Then you can decide on how you want to correct that.

For example, lets say your ambient lighting was later afternoon sun and it measured at 5150K, while your strobe measured 5500K. Thats a 400K shift between the two. If you used a 1/8 CTO which is a 300K shift, it would correct the 5500K strobe to 5200K, which is still 50K on the cooler side, but barely visibly noticeable. You could also go with a 1/4 CTO and get a warmer light from the strobe on your subject.

Basically, you can take two readings, and know exactly which gel to use without test exposures or guess work. I generally like about a 800K shift on the warmer side for my strobes hitting people to add a warmer skin tone. Generally I can get that on the first shot by measuring and then using the right combination of CTO gels. The same holds true for correcting fluorescents, halogen, tungsten, etc.

The down side is that color meters are expensive. However, it was really necessary when shooting film since visual testing was really a viable option. So learning how to read a meter, and doing the basic math conversions, allowed you to get spot on with the colors. I still do it this way since is so much faster than test exposures. But I find I can usually get right on with known light sources (ie, my strobes are 5200K, bright daylight, etc) and only need to measure when the lighting varies (various stages of sunsets, open shade, different bulb types, etc).

BTW, here are the shift values for CTO
2400K Full CTO
1200K 1/2 CTO
600K 1/4 CTO
300K 1/8CTO

CTB's work in the same way, but shift colors toward the cooler side.

Not sure where you obtained the shift values...

For example, Rosco, for 1/8 CTO, shows a shift of 5500 to 4900 or 600K
http://www.rosco.com …l.asp?order=so&​display=12

Actually, the "Mired" shift is not linear, byt differs based on the starting (source) light temp. Without getting into forulas, you can see this using the Lee calculator.
http://www.leefilters.​com/architectural/prod​ucts/mired/

I used my faulty memory rather then checking my notes Sorry. Here is the corrected values

Full 2600K
3/4 2300K
1/2 1700K
1/4 1000K
1/8 600K

Hi Robert, I just saw your thread. I have, for many years in shooting weddings, used a 1/4 CTO on my fill flash on camera while using 1/8 CTO on my highlight flash off camera. I find that it is often preferable for indoor scenes to have a bit of warmer-than-neutral look, as if shooting available light indoors, and find it more flattering to the bride. And the 1/8 CTO takes a bit of the coolness off speedlights. Just my opinion.

pcunite wrote in post #5723122
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.

Not an expert in this area, so please take this with a grain of salt, but I would think that outdoors, with plenty of ambient light, the 1/4 CTO might not look quite as "in your face" as it does in this controlled test. Yes, it will shift the ambient colour balance a little more to the blue end of the spectrum, but that might not be a bad thing...

Be careful with those CTOs

They can have a way of making people look like they're sitting under the french-fry heating lamps at Burger King.

I only use gels when i'm trying to match tungesten, and I might use it very late in the day if the sun's seeming very orange. I have one orange gel, I use that. Honestly i'm not looking for an exact match, just to get the temp into the vauge area of the ambient light, closer than 5500K. I don't think being really precise is necessary for portraits.

jrsforums wrote in post #5726283
Not sure where you obtained the shift values...

For example, Rosco, for 1/8 CTO, shows a shift of 5500 to 4900 or 600K
http://www.rosco.com …l.asp?order=so&​display=12

Actually, the "Mired" shift is not linear, byt differs based on the starting (source) light temp. Without getting into forulas, you can see this using the Lee calculator.
http://www.leefilters.​com/architectural/prod​ucts/mired/

sfaust wrote in post #5726676
I used my faulty memory rather then checking my notes Sorry. Here is the corrected values

Full 2600K
3/4 2300K
1/2 1700K
1/4 1000K
1/8 600K

Thanks guys. I'm doing a lot of reading and taking notes. As much as I'm understanding this, I'm still a bit confused.

Wilt wrote in post #5727260
Hi Robert, I just saw your thread. I have, for many years in shooting weddings, used a 1/4 CTO on my fill flash on camera while using 1/8 CTO on my highlight flash off camera. I find that it is often preferable for indoor scenes to have a bit of warmer-than-neutral look, as if shooting available light indoors, and find it more flattering to the bride. And the 1/8 CTO takes a bit of the coolness off speedlights. Just my opinion.

Thank you Wilt. I think I'm going to start with 1/8 and 1/4 CTO and then look carefully at the results.

Rudi wrote in post #5729402
Not an expert in this area, so please take this with a grain of salt, but I would think that outdoors, with plenty of ambient light, the 1/4 CTO might not look quite as "in your face" as it does in this controlled test. Yes, it will shift the ambient colour balance a little more to the blue end of the spectrum, but that might not be a bad thing...

Hi Rudi,

I have a feeling you're right and I'm going to go easy on the gels under I know better what the effects will be in different light.

Gentleman Villain wrote in post #5729448
Be careful with those CTOs

They can have a way of making people look like they're sitting under the french-fry heating lamps at Burger King.

LOLOL Yeah, I've already seen that and I don't think it's a very good look if you're not running the deep frier

tim wrote in post #5729716
I only use gels when i'm trying to match tungesten, and I might use it very late in the day if the sun's seeming very orange. I have one orange gel, I use that. Honestly i'm not looking for an exact match, just to get the temp into the vauge area of the ambient light, closer than 5500K. I don't think being really precise is necessary for portraits.

Hey there Tim,

As much as I want to understand this topic very thoroughly I do want to point out that my original intent was not so much to precisely balance flash against ambient light, but rather to give my subjects a pleasing warm skin tone. In my examples above, I found that either 1/8 or 1/4 seems to give me what I want and it's just a question of whether I get those same effects outdoors or if I need to go to a stronger CTO.

Whether something is necessary, in my opinion, is a relative and subjective thing since we all see things differently and have a different creative eye with different technical skills and requirements.

Robert, Wilt probably has it pretty close. Naturally personal taste is a big factor so I am looking forward to another test to see what you come up with. As an aside I was wondering if you had posted your impressions of the D300 somewhere, I don't want to hijack your thread with this but if you have a link I would be interested.

tim wrote in post #5729716
I only use gels when i'm trying to match tungesten, and I might use it very late in the day if the sun's seeming very orange. I have one orange gel, I use that. Honestly i'm not looking for an exact match, just to get the temp into the vauge area of the ambient light, closer than 5500K. I don't think being really precise is necessary for portraits.

Ah....a breath of practicality.....