which gel to use?

I am looking for a gel to turn my Canon 580EX flash into a match for tungsten lighting. I was told to look at "CTO gels". But a search turns up several. Which one is recommended? More precisely which strength? Thanks.

To do this correctly you need a color meter. One that can tell exactly what the color temperature is of a given source. Rarely do you find a single matched source. Most often you will find mixed light sources, ie some tungston from household lamps, some flourescent, and some daylight coming in through the window.

CTO = Color Temperature Orange converts daylight sources to tungston
CTB = Color Temperature Blue converts Tungston lights towards daylight.

Now you need to know that these are not the same types of filters used for theatrical lights. They are measured, and applied according to how much correction is required. Here is a good primer
from Lowell

http://www.lowel.com/e​du/light_controls/gels​.html

If you are shooting digital you can color correct in camera, in post as well as pre shoot, your choice.

So I assume converting my flash (assumed "daylight") to tungsten (indoor lights at a restaurant-type environment), I would use a CTO. Right?

Can I take 2 half-CTO and stack them to make a full-CTO gel? Is that how it works? I was thinking of getting a full sheet and cutting it to size, if I can stack them for when I need more color.

Am I thinking correctly?

You can order an entire pack of gel-modifiers using this link:
http://www.mpex.com/br​owse.cfm/4,5881.html

JChin wrote in post #12115040
So I assume converting my flash (assumed "daylight") to tungsten (indoor lights at a restaurant-type environment), I would use a CTO. Right?

Can I take 2 half-CTO and stack them to make a full-CTO gel? Is that how it works? I was thinking of getting a full sheet and cutting it to size, if I can stack them for when I need more color.

Am I thinking correctly?

You're on the right track, but you will either need a colorimeter to determine the actual color of the lights or do some experimentation. Not all lights that you would think may be tungsten lights actually are.

LBaldwin wrote in post #12114884
If you are shooting digital you can color correct in camera, in post as well as pre shoot, your choice.

Not always. If you're mixing flash and ambient in your exposure, you cannot color correct in camera or in post IF your flash in un-gelled (daylight) and the ambient is tungsten. If you're using your flash to overpower the ambient light, then yes you can color correct that. If it's mixed, you can color correct for either the flash or ambient, but not both. Mixed lighting like that is when you really want to use a gel so you have a single color temp in your photograph.

spkerer wrote in post #12115333
Not always. If you're mixing flash and ambient in your exposure, you cannot color correct in camera or in post IF your flash in un-gelled (daylight) and the ambient is tungsten. If you're using your flash to overpower the ambient light, then yes you can color correct that. If it's mixed, you can color correct for either the flash or ambient, but not both. Mixed lighting like that is when you really want to use a gel so you have a single color temp in your photograph.

With mixed lighting, I usually shoot a daylight balance photo without flash to see which is the dominant color cast. I then gel for that color cast. I also use this technique on flourecent lighting when I can't tell the color.

spkerer wrote in post #12115333
Not always. If you're mixing flash and ambient in your exposure, you cannot color correct in camera or in post IF your flash in un-gelled (daylight) and the ambient is tungsten. If you're using your flash to overpower the ambient light, then yes you can color correct that. If it's mixed, you can color correct for either the flash or ambient, but not both. Mixed lighting like that is when you really want to use a gel so you have a single color temp in your photograph.

Well said.....

spkerer wrote in post #12115333
Not always. If you're mixing flash and ambient in your exposure, you cannot color correct in camera or in post IF your flash in un-gelled (daylight) and the ambient is tungsten. If you're using your flash to overpower the ambient light, then yes you can color correct that. If it's mixed, you can color correct for either the flash or ambient, but not both. Mixed lighting like that is when you really want to use a gel so you have a single color temp in your photograph.

You are correct, BUT if you shoot and stack you can color balance indivdual images and then stack as needed, match the color and then the editor is in Love with you...

I used to do it the old fashioned way, But now I can take 3 images, or more and color correct, density correct and add or remove elements to my liking. You don;t seriously think that all those beautiful shots in Architectural Digest are done in camera only with one shot?

I wish I could show you some of the stuff I have done lately but legalese prevents me from doing so. To tell the truth the gels are actually the hard way of doing it. You have color temp issues, exposure variations and worst of all heat buildup. Use the color temp selections in PS on each indvidual image and stack em. It does make for a fatter file tho.

OMG! Did I open a can of worms?

All I want to do is not have a drastic color difference between the ambient light and my flash. Something that will just bring my flash closer to ambient tungsten lighting (say about 3000K).

No you didn't open any cans... there is just more than one way to do this. If you decide to gel, you have also do some exposure correction. If you use multiple images, you have to stack and edit. If tou use a color meter you have to have enough gels to make the corrections - and voltage in the lamps can alter that too. Color correction is a HUGE can of worms, you just peeled back a bit and peeked inside.

If you gel the flash your skin tones may not look so hot. The same with some fabrics. White dresses, colored hair, certain skin conditions and paints on the wall can get really wonky. I shot a car once that had to be done under mercury vapor. No other lighting was allowed, and I had to have minders around to car at all times. The freakin paint changed colors from just about any direction... I also once had a nasty shift in color for a window film no matter what I did it rainbowed, and the editor wanted those windows in nearly every shot. If you are using on camera flash don't slow down the shutter speed too much.

I recently did some shots of my wife cooking in our kitchen using a combination of tungsten ambient lights and wireless flash. Background of kitchen was orange relative to a daylight wife. Solution:
1. Place full CTO gel over flash (you can use two 1/2 gels stacked, but you use a little more light that way).
2. Change camera white balance to tungsten. Otherwise, everything comes out looking orange.
3. Shoot and then check camera display. Should look just about right, and then any fine tuning can be done in post processing.

Another very effective use for CTO gels is in flash portraits. Using a 1/4 CTO on the flash and auto or daylight white balance gives the subject a subtle warmer glow.

HughR wrote in post #12116438
I recently did some shots of my wife cooking in our kitchen using a combination of tungsten ambient lights and wireless flash. Background of kitchen was orange relative to a daylight wife. Solution:
1. Place full CTO gel over flash (you can use two 1/2 gels stacked, but you use a little more light that way).
2. Change camera white balance to tungsten. Otherwise, everything comes out looking orange.
3. Shoot and then check camera display. Should look just about right, and then any fine tuning can be done in post processing.

Another very effective use for CTO gels is in flash portraits. Using a 1/4 CTO on the flash and auto or daylight white balance gives the subject a subtle warmer glow.

Thanks for the info. That doesn't sound too hard to do and is about what I was hoping to do.

So is full-CTO a good starting point or should I buy 1/2-CTO?

I have full CTO, 1/2 CTO, and 1/4 CTO, but I mainly use 1/4 for portraits and full CTO to balance tungsten. Lumiquest sells a kit with these plus blues, greens, a red, and a yellow gel along with a holder to put them over the flash. Check out Lumiquest (or Honl) on the web.