"School of Portraiture" - Lesson 07 - Introduction to Gels

[Colin Southern]

A good time for colourful outdoor portraiture is around sunset / twilight. Around this time the background can get very colourful, but output from our flashes are usually daylight balanced, and this gives us two vastly different coloured light sources, which can work "OK", but if we change the colour of the light coming from the flash by putting a coloured piece of plastic in front of the light (called a gel), then we can really start to mix things up a bit.

Gels come in all colours, but the two most common are called CTO (Colour Temperature Orange) and CTB (Colour Temperature Blue); for flashes they're typically about 6 inches long, and a couple of inches high, and you just bend them around the flash head and hold them in place with duck tape / velcro / ruber band etc. Some flashes have proper gel holders, and for others you can download fancy templates so you can cut gels to the exact size/shape, but in reality, they all work the same; it doesn't have to be pretty - it just has to work! They also come in different strengths, typically 1/4, 1/2, and "full" - so if someone says they used a 1/2 cut CTO gel you'll know it was a 1/2 strength orange gel (like I've used below).

So lets take a quick look at how gels work:

Lets assume we have a typical sunset with rich and colourful reds and oranges. If we take a shot with this lovely scene behind our subject - and reflect some of this light back onto the face of our subject - then the reflected light will be the same colour, and the subject will take on some of this character. If we use flash instead of a reflector though, the light hitting the subject will be much whiter, and the skintones of the subject - although technically accurate (assuming we white balance to the flash light) - will none-the-less result in a subject that looks "out of place". So a CTO gel helps to balance the subject with the background - but - wait, there's more ...

... If one then shifts the colour temperature of the shot in post processing towards cooler (by adding blue) then skintones will shift from quite orange towards more natural. Unfortunately this also adds blue to the sunset and starts to neutralise the reds and oranges - but - it also adds blue to an already blue sky, thus resulting is highly saturated "lush" blues (especially if you under-expose the background slightly). Take a look at this shot as an example ... I've used a 1/2 cut CTO (so only "1/2 strength") - adjusted for a relatively normal skintone - and I STILL had to knock back the saturation by 50%! So it's powerful stuff; allowing you to get dramatic shots right out of the camera.



CTB (Colour Temperature Blue) works the opposite way ... adding blue to the subject - which means you must add orange in post processing to offset it; that orange also gets added to the background diminishing the saturation of anything blue, but adding to the satuaration of anything red / orange, and again, you get far more dramatic colours than you would of without using a gel.

In this first shot, my gelled flashes didn't recycle fast enough, and thus I was able to get an accurate white balance from the showing shoot-through umbrella; The colour temperature is 7500 Kelvin. Pretty "dull and boring" colours.



In this 2nd shot, the gelled flashes do fire, and the scene correctly white balances at 4100 Kelvin. Look at the diference! (and that's just a 1/2 cut of CTO gel!) (Although I should probably add that this isn't necessarily a perfect out of the camera shot, but it's certainly a better place to start from than the one above).



On a final note, I thought I'd include a couple of shots just to show you how much work the flash is really doing; in the first of the two, the flash didn't fire, and I haven't attempted to adjust the scene in any way (keeping in mind here we're shooting into the light too) ...



and here in the second - with the umbrella visible - you get a good feeling for the light it's throwing on our subject ...



Hope this helps

Happy to answer any questions!

[tihsgod]

Colin, thanks, that really is very interesting.. I even read it twice

[Mohamed]

Thank you Colin,
Very beneficial, I have read all of the flash articles you listed here but did not buy anything yet. I will have to read it all over again after I buy my toys .

I appreciate it very much. Thanks

[Colin Southern]

Colin, thanks, that really is very interesting.. I even read it twice

I read it several times myself!

[Colin Southern]

Thank you Colin,
Very beneficial, I have read all of the flash articles you listed here but did not buy anything yet. I will have to read it all over again after I buy my toys .

I appreciate it very much. Thanks

You're very welcome Mohamed. Let us know if we can help with gear purchase.

[wilgk]

Thankyou! ....just when we thought it was safe to go back in the water...lesson 7 bites

How thick are the gel thingies - as in not just like a piece of cellophane I'm guessing....but thats how i'm thinking of understanding how they work, remember when as kids if ever there was orange or that deep purple cellophane around, we always used to wrap it across our faces to see what 'colour' we became....(or did just Southlanders do that?)

The amount of light generated is amazing.

[Colin Southern]

Hi Kay,

Yeah - just thin plastic sheets. A little bit more rigid than cellophane, but very similar.

[speedneeder]

Good stuff Colin. Thanks

I hadn't though about using gels like that, very interesting!

[Antonio Correia]

Excellent Colin, Excellent

[Colin Southern]

Thanks Brian and António

[wilgk]

A new question - why the umbrella and not softbox on the light - specially due to wind at the beach?
Just thinking aloud that maybe 1 day I will want to get 1 or the other ...was hoping not to need both...or someone near and dear to me was anyway.

[speedneeder]

Very funny Kay! I was just discussing with my wife last night my 'need' for a flash, stand, and softbox to add to my brand new umbrella rig...
Good thing my birthday is coming soon LOL

[Colin Southern]

A new question - why the umbrella and not softbox on the light - specially due to wind at the beach?
Just thinking aloud that maybe 1 day I will want to get 1 or the other ...was hoping not to need both...or someone near and dear to me was anyway.

Hi Kay,

I was going to use softboxes, but that means using studio lights, which inturn means bringing 230v generator(s) onto the beach. I was pretty confident that we could do that safely (with several additional safety precautions) (230v strobes being hand held over sea water is a "cause for concern"!), but I wanted to check with a registered electrician / fellow photographer / friend first, and I didn't hear back from him in time.

In reality the dual 580EX II setup is "rarely lacking" in output though, as you can see.

[Colin Southern]

Very funny Kay! I was just discussing with my wife last night my 'need' for a flash, stand, and softbox to add to my brand new umbrella rig...
Good thing my birthday is coming soon LOL

Just let me know if you need me to sign a permission slip!

[Class A]

Very nice pics, Colin.
It hadn't occurred to me that one could use gels to influence the background WB by compensating for the gel tint in post. I just thought of gels as being a way to simulate sunlight, for instance. The technique you described has much more impact.

Thanks for sharing!

BTW, where did you get your gels from?

I've read that one can get free samples from some manufacturers and that one rarely needs more than these samples. Maybe that's a USA only story...

[Class A]

BTW, I couldn't add this to "Lesson 6" about Studio Lighting anymore. Please let me know if you want me to remove it from this thread.


Shot in a studio with two softboxes and a hair kicker.

[wilgk]

Hi Kay,

I was going to use softboxes, but that means using studio lights, which inturn means bringing 230v generator(s) onto the beach. I was pretty confident that we could do that safely (with several additional safety precautions) (230v strobes being hand held over sea water is a "cause for concern"!), but I wanted to check with a registered electrician / fellow photographer / friend first, and I didn't hear back from him in time.

In reality the dual 580EX II setup is "rarely lacking" in output though, as you can see.

Aah I'm understanding which goes with what, and where now.....Thankyou

[Colin Southern]

Aah I'm understanding which goes with what, and where now.....Thankyou

Hi Kay,

I've seen softboxes for battery-powered strobes, but I really can't see any advantages over a shoot-through brolly, at a fraction of the cost. Quality softboxes have features like double-diffusers, and I don't think the likes of a single 580EX would have enough grunt to work properly.

[wilgk]

yep understood - I think my 'toe in the water' might be the shoot through brolley with the 'strobe on a stick' ...trick.
I have only 1 strobe atm as well of course.

[Colin Southern]

yep understood - I think my 'toe in the water' might be the shoot through brolley with the 'strobe on a stick' ...trick.
I have only 1 strobe atm as well of course.

Tell hubby I said you need more - at least 4

Seriously, 1 is fine. I usually use two, but they work together so each one is only working 1/2 as hard. I do have 2 more as well for a second rig, but I seldom use it because it means another assistant (who would moan about getting cold / wet feet / bored etc); so for outdoor stuff like this I tend to just run with either flat lighting along the camera axis or something more directional, but accept the fact that I might get more contrast than may be desireable.