When And Why Would I Use CTO Gels?

[TMR Design]

In the reading and DVD's I've been watching I notice that CTO gels are used quite often. I believe CTO is acronym for Color Temperature Orange but I really don't understand what that means.

What exactly are CTO gels? When do you use them? When do you use a CTO vs. 1/2 CTO?

[viperx27]

lots of scenarios call for them, but in general its to balance ambient and flash color temp. the flash is much cooler in general, and this will warm it up. so anytime you want a warmer color temp from the flash they're great. which one you use (there's also 1/4 and 3/4 etc) depends on how intense you want it.

[cdifoto]

CTO gels convert daylight to tungsten. Helpful when you want to match a hot shoe strobe to the ambient light so that everything is "correct" right down to the sconces on the wall.

[TMR Design]

Thanks.

How much of a pain in the arse would it be to ask to see an image that was not color temperature corrected and then one with the correction?

Is it standard practice to use the gels on location? Why does this come into play with hot shoe flash and not studio strobes? Do you get good at knowing which CTO to use through experience or are there some basic starting points to get started, that you then tweak as you go?

[viperx27]

don't think I have an actual test showing the difference (though I wold suggest you doing that).

Heres a shot in open shade, very very cool color temp (you can see the blues in the shadow areas) but used a Full CTO + yellow gel over a speedlite off camera to simulate sunset light.

http://img.photobucket.com/albums/v721/viperx27/Brooks/39651923.jpg

[Wilt]

Thanks.

How much of a pain in the arse would it be to ask to see an image that was not color temperature corrected and then one with the correction?

Is it standard practice to use the gels on location? Why does this come into play with hot shoe flash and not studio strobes? Do you get good at knowing which CTO to use through experience or are there some basic starting points to get started, that you then tweak as you go?

Boy are you being a pain in the arse! ;) Saw this too late to do this tonite, and won't have a chance until Saturday.

I normally put a 1/4 CTO into my on-camera flash to warm the light a bit, as that is more flattering to the bride. I also have a 1.8 CTO into my off-camera flash so that highlight is just a touch cooler on the bride. A full CTO would take 5500K daylight source and correct it to tunsten 3200k. The Rosco book tells you the degree of correction with staring color temp and ending color temp, taking most of the guesswork out of it. The 1.8 CTO that I use takes it to 4900K, and the 1/4 CTO takes it to 4500K.

If you are shooting where there are fluorescent fixtures in the room, you can also put one of the greenish Rosco Plusgreen so that when you correct later during postprocessing, the overall light will be more uniform.

[viperx27]

A lot of when and how much comes down to knowing color temp guides and the color correcting guide.

Typical color temps:
1500 K Candlelight
2680 K 40 W incandescent lamp
3000 K 200 W incandescent lamp
3200 K Sunrise/sunset
3400 K Tungsten lamp
3400 K 1 hour from dusk/dawn
5000-4500 K Xenon lamp/light arc
5500 K Sunny daylight around noon
5500-5600 K Electronic photo flash
6500-7500 K Overcast sky
9000-12000 K Blue sky

Color chart, one corrects the opposite color (magenta cancels green and vice versa )
http://img.photobucket.com/albums/v721/viperx27/color-1.jpg

more color info, addative and subtractive color chart. red/green/blue makes white, cyan, yellow, magenta make black, and you can see the color inbetween


http://img.photobucket.com/albums/v721/viperx27/ColorChart1-1.jpg

[suyenfung]

580ex, shoot through, full cto. ordinary light bulb in lamp, mid-afternoon light through the windows.

http://www.jarredwagner.com/images/uploads/shared_archive/pcb/07.11.22_17.02.12.jpg

[René Damkot]

Thanks.

How much of a pain in the arse would it be to ask to see an image that was not color temperature corrected and then one with the correction?

Is it standard practice to use the gels on location? Why does this come into play with hot shoe flash and not studio strobes? Do you get good at knowing which CTO to use through experience or are there some basic starting points to get started, that you then tweak as you go?

It comes into play with studio strobes as well.

You could color correct the shot later, unless you are mixing light sources: Tungsten ambient wirh a bit of fill flash for instance. Without the gel, you have two choices: Blue fill flash or orange ambient...

[TMR Design]

Boy are you being a pain in the arse! ;) Saw this too late to do this tonite, and won't have a chance until Saturday.

I normally put a 1/4 CTO into my on-camera flash to warm the light a bit, as that is more flattering to the bride. I also have a 1.8 CTO into my off-camera flash so that highlight is just a touch cooler on the bride. A full CTO would take 5500K daylight source and correct it to tunsten 3200k. The Rosco book tells you the degree of correction with staring color temp and ending color temp, taking most of the guesswork out of it. The 1.8 CTO that I use takes it to 4900K, and the 1/4 CTO takes it to 4500K.

If you are shooting where there are fluorescent fixtures in the room, you can also put one of the greenish Rosco Plusgreen so that when you correct later during postprocessing, the overall light will be more uniform.

Thanks Wilt. I look forward to seeing those images.... pain in the arse that I am :D

[TMR Design]

580ex, shoot through, full cto. ordinary light bulb in lamp, mid-afternoon light through the windows.

http://www.jarredwagner.com/images/uploads/shared_archive/pcb/07.11.22_17.02.12.jpg

Thanks Jarred.

It comes into play with studio strobes as well.

You could color correct the shot later, unless you are mixing light sources: Tungsten ambient wirh a bit of fill flash for instance. Without the gel, you have two choices: Blue fill flash or orange ambient...

Hi René. Thanks for the info. Using gels to correct color temperature is new to me but I'm starting to gain an understanding of how useful and important it can be. I always prefer to shoot the best image with the best color possible and only use PS when I have to rather than relying on it as a post-processing 'fix'.

I have a feeling that once I get my CL-4 I'll be checking out CTO gels.

[Wilt]

Another example of using gels on location...

You have an interior shot where you wish to capture the ambience of the lighting that is already there, but you want more intensity without obvious addition of supplemental lights. So you unscrew the normal incandescent bulbs in a few fixtures and replace them with AC electronic flash units, putting gels over them to bring them to 3200-3400K color balance, then shoot.

[ghostman]

Strobist mentions CTO gels here:
http://strobist.blogspot.com/2006/03/lighting-101-using-gels-to-correct.html

There's also a video of a photoshoot on the site where the photographer uses CTO gels. I forget which video though, so watch them all! :-p

[canonphotog]

Another example of using gels on location...

You have an interior shot where you wish to capture the ambience of the lighting that is already there, but you want more intensity without obvious addition of supplemental lights. So you unscrew the normal incandescent bulbs in a few fixtures and replace them with AC electronic flash units, putting gels over them to bring them to 3200-3400K color balance, then shoot.

Is this "AC electronic Flash unit" something that screws into the light socket in place of the light bulb? If so, please provide a link if possible.

Off to "search" in the meantime.:)

[Curtis N]

Robert,
Have you seen this thread (http://photography-on-the.net/forum/showthread.php?t=218280)?

[Wilt]

Is this "AC electronic Flash unit" something that screws into the light socket in place of the light bulb? If so, please provide a link if possible.

Off to "search" in the meantime.:)

http://www.bhphotovideo.com/bnh/controller/home?shs=AC+strobe&ci=0&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=RootPage.jsp&A=search&Q=*&bhs=t

[TMR Design]

Robert,
Have you seen this thread (http://photography-on-the.net/forum/showthread.php?t=218280)?

Thanks Curtis,

I actually had read that thread quite some time ago when it did not register. I just re-read it and now I'm beginning to understand things a bit more. I'm going to have to try some shooting with the various CTO gels and experiment a bit.

[canonphotog]

http://www.bhphotovideo.com/bnh/controller/home?shs=AC+strobe&ci=0&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=RootPage.jsp&A=search&Q=*&bhs=t
Thanks Wilt! I'll have to give a few of those some thought. Might be useful someday.

[Unity Gain]

I love it when CTO gels are used like this:
http://www.flickr.com/photos/jwlphotography/728414751/in/set-72157600249818434/

[jrsforums]

[quote=Wilt;4455387]...A full CTO would take 5500K daylight source and correct it to tunsten 3200k. The Rosco book tells you the degree of correction with staring color temp and ending color temp, taking most of the guesswork out of it. The 1.8 CTO that I use takes it to 4900K, and the 1/4 CTO takes it to 4500K...[quote]

Hi, Wilt....

My Rosco Cinegels, and their web site, have different conversions....full CTO converting 5500 to 2900. See: http://www.rosco.com/us/filters/cinegel.asp

Actually you are probably hampered by your years in the business, when all the gel guys quoted conversion from 'Daylight' which was the cinematographer's 'Daylight' at 6500....which I believe Lee still does. CTO from 6500 'daylight' will give 3200 as the result.(see: http://www.leefilters.com/lighting/products/finder/ref:C46DD2D59CE24F/ select the '204' full CTO and hit 'Colour Details' )...and when they wanted to go to match hot studio lights which were designed at 3200 (probably why Canon still uses it for Tungsten....even though most homes and venues are much lower than that.

One other point. The Rosco CTO are a bit red...I usually use CTS which are the same conversion, but less red (more like Lee CTO).

One good site to see examples is 'planet Neil'
http://planetneil.com/tangents/
http://www.planetneil.com/faq/flash-with-tungsten.html

[suyenfung]

I love it when CTO gels are used like this:
http://www.flickr.com/photos/jwlphotography/728414751/in/set-72157600249818434/

oh snap! feelin it.

[bieber]

There are basically two uses for them: color correction and color de-correction, I guess you could call it. The first is simply making all your color temperatures match; i.e., if you're shooting with some tungsten lights, you want to change the temperature of your flash to tungsten. You can, of course, correct white balance in RAW, but if you have multiple color temperatures in the scene, you'll only be able to get one correct at a time, unless you composite multiple RAW conversions. It's definitely helpful to set your camera's white balance to tungsten, but as long as all the color temperatures match, it'll be easily correctable if it's off a little.

You can also use them, of course, to create a deliberate color imbalance. For instance, in the shot I'm attaching, I put a full CTO strip over the light that I put on my subject, and then set white balance to tungsten. That made the subject properly balanced, but made the background look really blue by comparison. I've also seen it applied interestingly in indoor portraits, with the aid of a CTB gel as well. Light the whole room with one light with a CTB gel, then use a grid-spot, snoot, barn-doors or whatever to put a CTO gelled light just on your subject, set your camera's white balance to Tungsten, and you've got some nice color contrast. If you're stuck shooting someone doing something relatively boring, and absolutely can't think of anything interesting to do with the scene at hand, it can at least help to add some interest to an otherwise utterly boring shot.

[TMR Design]

Very cool. Lots of great info and input. Thanks Robert.

Rather than create another thread I'll just ask my next question here.

If you're using a strobe (Alien Bees B800 in my case) with a speedring and softbox, how do you attach a CTO gel? Normally it's attached to the strobe or the reflector but that's not possible with the speedring and softbox.

What method do you use?

[Wilt]

Big gel, clamped onto the outside of the softbox

[TMR Design]

Wow, really Wilt? You wouldn't try to rig something up so the gel sat right in front of the flash tube and outside of the speed ring? I would need a gel that is 24" x 32"?

[Wilt]

Wow, really Wilt? You wouldn't try to rig something up so the gel sat right in front of the flash tube and outside of the speed ring? I would need a gel that is 24" x 32"?

It would very much depend upon the design of the flash unit! If you used a unit which permits the removal of any hood so that you could insert the head into the softbox as a bare tube unit, it would be hard to jury rig something! If you have a unit which has a non-removable hood, that offers a better way to deal with gels, but at the expense (I think) of uniformity of light compared to the bare tube head. If you have a softbox with a removeable front, and an intermediate diffuser (double diffusion softbox) for best uniformity across the front of the box, you could rig a smaller gel to the inner diffuser. My original reply was a general and simplified response.

In any event, my major issue with the approached I have just identified is that it is not QUICK to set or to replace with alternate filtration! The exterior approach is better for time, and for a pro time is money.

[TMR Design]

That makes a lot of sense Wilt. So if I have gel sheets that I can clip to the inner diffuser that should work and I agree that it's a better solution than having to get to the actually speedring or strobe.

[Franko515]

Here are two articles that may help ya out.

http://lightingmods.blogspot.com/2007/11/flash-gels-for-correcting-color.html

http://lightingmods.blogspot.com/2007/12/flash-gels-for-correcting-color.html