Lighting 102: CTO Assignment | Discussion

Report from June 3rd, in which you were asked to use a CTO filter to do something other than correct for incandescent light. The CTO is maybe the most useful CC filter in the whole pack, as several readers demonstrate in their photos, after the jump.

Greg Cee shot on tungsten white balance and gelled his flash with a CTO -- but went with an additional 1/2 CTO (full CTO plus a 1/2 CTO) gel on the thin sliver of light coming from camera right.

This is important, as it puts the light past normal and into a warm color, which is nice when you are making it try to stand out against the blue you have gotten by shooting on incandescent WB.

Fill was from an umbrella, no gel, and pointing up to feather the light off of the bottom of the frame.

Takeaway: If you are trying to do that cool-light shift thing, with a CTO on your light, go past full CTO to either (2) CTO or (1.5) CTO to get that warm-on-cool light that usually looks better than white on cool.

What's the one day a year when you can cover your kid in spaghetti and not catch trouble?

Father's Day, of course. Especially your very first Father's Day, which is when Brad Herman chose to reproduce a photo he had seen done long ago, this time using his kid as the model.

Brad used a palette of warm-to-neutral light: Full CTO on the spaghetti monster, half CTO shooting through the tree in the background, and a no-CTO rim.

That last one is assuming he was on incandescent WB, but looking at it now I am not totally sure. Reason is, the full CTO front flash looks pretty warm for a straight CTO in tungsten WB mode. And the rim light does not look quite full CTB.

I am guessing he either walked the WB around a little in between, or shifted the color a little bit in post. Maybe Brad will clue us in via the photo's caption.

Either way, this is the kind of photo that will make someone pick up the phone and call someone at a kid's modeling agency. Or social services. We trust the bath followed shortly thereafter.

Also going for the 1+1/2 CTO thing on tungsten WB was jgentsch, which allowed him not only to deepen the sky's blue tone, but to contrast it nicely with warm light (even after the WB conversion) on the flowers and window.

Thanks much for the setup shot, too. Those are always helpful for people to see. Although there is a bit of a setup shot in the original photo, in the camera left window...

Shutter-Think skipped the incandescent WB shift and decided to go warm and warmer in his photograph of a woman practicing yoga.

He went the other way, balancing to shade. The half blue gel on the main light brought it back closer to daylight.

But it caught a lot of warm bounce fill and warmed up from a backlight gelled full CTO, made even warmer by the camera's shade WB setting.

Remember, with the combination of full and partial CTOs and CTBs, you have quite a range of options to dial your photo warmer or cooler. And you can do it for the whole photo, or vary the shift with each light.

And finally, this self portrait by nikonbhoy works all around the warm/cool scale, using a full CTO front light, a blue backlight, and daylight ambient fill.

It was shot on tungsten WB, which shifted everything toward blue.

As a group, these photos do a great job of showing some of the different looks that are possible using a couple of sheets of orange-ish acetate, once you realize that stuff is far more useful than just correcting for tungsten light.

Really nice work, guys. You can see the original assignment here, and all of the entries here.

UPDATE: From the comments, a little confusion as to which Rosco filters are what, WRT CTO's, CTB's, etc. Also from the comments, a heads-up about an excellent Rosco publication containing such info. (Check out page nine.)

NEXT: Lighting 102: 7.0 -- Time-Based Variables


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Anonymous fredericksburg wedding photographer said...

Does anyone know how the various CTOs used (1/4, 1/2) compare to the Nikon gels (TN-A1, A2; Amber)?

June 27, 2008 11:26 AM  
Anonymous Anonymous said...

exactly what does "1 and 1/2 CTO" mean?

June 27, 2008 12:25 PM  
Blogger GeoDesigner said...

Hello Dave,

Since we the poor guys who learn at Strobist almost always use the Rosco gel sample packs, how about writing a post about the alternate names for them written on the little swatches (they are not called CTOs or CTBs on them)? I Believe the "Amber" gel (Roscolux) is the equivalent to the CTO, for example.

June 27, 2008 1:10 PM  
Blogger sallenschneider said...

what exactly does "1 and 1/2 CTO" mean?

June 27, 2008 1:30 PM  
Anonymous Mike Perrault said...

On the picture of the flowers. Will this work in the daytime to bring a nice deep blue sky into play? Use a high shutter and pull down the ambient, but it often seems to get kinda gray when I do that.

If you'd only have used +1 CTO would the "whites be whiter" instead of so warm? Would it keep the blue sky?

June 27, 2008 2:15 PM  
Anonymous Richard Cave said...

That last photo awesome, the kid with the spaghetti get that in stock now there is money to be made there!

That last photo is haunting me, I am now looking for to emulate that feel,


June 27, 2008 2:40 PM  
Blogger Balmore said...

To answer some of the questions:

1 and 1/2 CTO (also 3/4, 1/4 & 1/8 CTO):
CTO gels (and others) come in various strengths to warm (cool or colour) the light by different amounts. A full (1) CTO will convert daylight (and flash) to Tungsten, a 1/2 CTO will get you half way there. if you where to stack a full CTO and a 1/2 CTO you would over correct and the light would be warmer still.

you can stack then to make up the amount of warming you require:

1 (full) CTO = 1/2 CTO + 1/2 CTO
or any other value you want.

Rosco Filters:
I have a rosco sample pack (and a number of gel sheets) in CTO and its other strengths.

Hope that helps.


I'll squeeze this in at the end and it will confuse more than it helps. A (full) CTO will convert a (Cool) Daylight source at 5500­K (Kelvin) to the same spectral output as a (Warm) Tungsten source at 2900K an apparent temperature drop of a mere 2600K (or centigrade).

June 27, 2008 3:49 PM  
Blogger cliquephotodesign said...

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If you all don't know about you're swimming upstream. Great site to watch every week. and the 138 previous episodes are well worth the $99 membership. Email me if you all have any questions.

June 27, 2008 3:55 PM  
Anonymous george said...

anon 12:25 and sallenschneider 1:30;

CTO means Color Temperature orange. The 1 is the level necessary to turn the flash color temperature to that representative of a tungsten bulb, 1/2 is self explanatory.

Mike perrault 2:15;

#1 yes (ambient to blue) everything outside the flash range will be bluer/ish as long as camera/photoshop is set to tungsten.

#2 yes

June 27, 2008 3:58 PM  
Anonymous MLS said...

In response to some of the previous posts:

Many of your questions can be answered in David's article "Using Gels to Correct Light" in the Lighting 101 section.

Rosco has an excellent PDF called "Filter Facts." Cruise their website and download it. It's chock full of info and lists the item number for the various color correction gels. (For example, a full CTO = 3407) I'm sure the Lee website has similar info.

June 27, 2008 4:28 PM  
Blogger Steven W. Hopkins said...

I just listened to your lastest Lightsource podcast interview and I am confused. You said you find out what the correct exposure for a room is, and then drop it a stop or two. then you said you put in the fill flash somehow, and then drop that a stop or two. Are you saying that you stop down twice? Or are you just add the fill to the ambient and then dropping them both down at the same time?

June 27, 2008 7:36 PM  
Anonymous Anonymous said...

In my opinion The Light Whisperer created an excellent example again from what I understood the lesson as. If you haven’t seen it here is a link Unless that was not what the lesson was suppose to be.

June 28, 2008 3:07 AM  
Blogger Michelle said...

Typical - trust me to miss the assignment!

June 28, 2008 4:04 AM  
Anonymous Anonymous said...

fredericksburg wedding photographer said...
Does anyone know how the various CTOs used (1/4, 1/2) compare to the Nikon gels (TN-A1, A2; Amber)?

I also want to know the same thing....

June 28, 2008 10:14 AM  
Anonymous moritz said...

Anonymous and fredericksburg wedding photographer: strong advice on the Nikon SJ-1 "original" gels - if you don't own them already don't buy them! I bought a pack, thinking it must be quality since it is an original Nikon spare part and they are pretty useless. The idea is that the sign/abbreviation after the type name tells you how to set your white balance. For the FL-G1 you set your camera's white balance to florescent (the little striplight sign, similar to a "full window green"), for the TN-A1 you set it to tungsten (the little light bulb, similar to a full CTO). These two are supposed to help you balance with ambient light. All the others are meant to colorize the effect of your flash light on the image to a greater or lesser degree (i.e. warming up your light a bit with the TN-A2, similar to a 1/4 CTO, or really colouring it completely red or blue). That's why it says AWB on those, they are supposed to effect the light colour. You would expect that, since it is original Nikon ware, the TN-A1 and FL-G1 are very well balanced with the camera's white balance presets. This is not the case, the flash tends to produce murky off-colours with both the gels. You will be better and cheaper off with a set of Rosco gels as mpex sells them. The colour temperature they state on the enclosed list can be trusted and with a bit of crafting the will also stay on your flash more reliably than the flimsy SJ-1

December 18, 2008 4:20 PM  
Blogger GfK said...

what about autoWB
that is supported by Nikon's gels on D700 and D3 ??
It is very very convenient.
The flashgun reads the gel you supplied and sets the WB of the camera to the appropriate setting.
Is this possible with 3rd party gels ??

April 29, 2009 4:11 AM  
Blogger Brian Lance said...

For anyone else looking for it, the Filter Facts document is now at

February 17, 2010 6:33 PM  

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