What’s the difference between using a green gel and no gel?

01 六月, 2016

作者: Jared Platt

What’s the Difference? is a series of lighting tutorials. Each article responds to a single question. In this post, Jared Platt explains the difference between using a green gel and no gel.

In my last post, I detailed the process of using color correction gels to match the colors of various light sources. It that case, we matched the flash (which is a slightly blue light) to overcast daylight (which is much more blue). Then we went the opposite direction and intensified the blue in the sky, by using a warm gel on the flash. If you haven’t read it, take a look, it is worth the read.  Throughout the shoot, we nailed four variations that were are great, so the selection between them would be based on individual preference.

In our next challenge, we will be correcting light that is not a matter of preference. In fact, without a corrective Gel on this shot, you may as well pack it up and go home, or do a lot of work in Photoshop when you get home. But with the right gels on your flash, the ugly light we encountered on this photoshoot is no problem whatsoever.

We took our model to the Arizona Railway Museum which sports a shiny railway car from the 1960’s, complete with beautifully hideous florescent lights from that decade. This is the color of light you can see and feel as odious with the bare naked eye. You know it is sucking your soul when you walk into the room, and it photographs with the same evil intensity. Of course you can find this kind of lighting in many corporate environments as well, although you will find that florescent lights have made some major breakthroughs in color temperature in this century. So the idea that all florescent bulbs are all evil is becoming less true as manufacturers have taken the temperature of CFL to exciting new lows, below 2700 K. Because of these advancements in technology, you can’t make a blanket statement that all florescent light will be at the wretchedly ugly temperature of 5000 kelvins. Now you need to do a little research into the temperature of your light sources.

When I say research, I mean, point your camera at the bulb in the daylight white balance mode and take a photo. Is it green? Is it orange? Is it Neutral? This will give you a good indication of what color that light is.  You can even go to the custom white balance mode and dial the kelvins up and down in “live view” mode and watch the color of the light change as you dial the temperature up and down. This simple activity will give you an accurate understanding of your color temperature wherever you are. We went looking for an ugly florescent scene and actually found that most of the newer corporate offices around Phoenix were using much warmer CFL and LED lights, so we decided to go back in time to 1960 inside this Amtrack express train and we definitely hit the jackpot for ugly light! (Please don’t read this as me putting down the train museum, they have done a great job at preserving the cars, which is why I was confident I could find the color of light I was looking for).

When gelling is a must

If you recall my color of light discussion from my last post, you will know that a flash is the same color temperature as the sun at midday with no clouds (5500 K) and will match that slightly blue color. But when you use a flash indoors and white balance for the flash on the model, you will end up with a neutral subject and a color tinted background. If the ambient light inside is created with incandescent bulbs or soft white LEDs, you will have a very warm background. If it is lit with daylight balanced CFLs, there will be no color cast at all. If, however, you show up at a corporate photo shoot and they are lighting their facilities with standard florescent bulbs (5000 K), you will end up with a very ugly green background! Unlike my last photoshoot, where the choice between the color casts were completely subjective, no one wants to look at the green cast of a florescent light! So you had better use a gel.

The original setup

In this case, we had three lights for the shot. The main light was a Profoto B2 Off Camera Light, modified with a 2 foot OCF Softbox Octa with a soft grid. We used the soft grid to keep the light from spilling out beyond the model. We wanted to see the ambient light, in all it’s glory. We also employed a Profoto B1, modified with a Zoom Reflector (right behind the model and low enough not to be seen) to give him a hair light and to add a little rim to the seat backs throughout the train car. Then we added a second, bare headed B1, with only the Gel Holder to create some additional forward light from the back of the train car.

 

In our first shot, we did not gel the flashes and we selected the flash white balance setting on the camera (Canon 5D Mark III with a 24-70 2.8L lens). The exposure is set at ISO 500 at f 2.8 and the shutter speed is a long 1/40 second, to burn in the ambient light on the train. The model and the first set of seats is lit by the flash, and therefore the color of the flash is over ridding the ambient green. Behind him, throughout the rest of the car, you see the true ambient color in full display. The only other instances of neutral color you see are the rims and reflections of light from the B1 off camera flashes behind the model.

Adding the green gel

Now that I have your attention! It’s time to solve this problem. By adding a Green gel to each flash and then switching the white balance on the camera to florescent, we matched the two colors of light. Now the same ugly light that is coming from the florescent lights on the train is also emanating from the flashes. That’s right! We want the same ugly color coming from our flash that is coming from the train lights. So when the camera corrects for green, all of the green is corrected at the same time, and my model and my background are both brought back to neutral.

 

The conclusion

You can see that adding one simple gel to three lights will correct a very ugly problem very quickly and remove a lot of wasted time in post-production. The Profoto OCF Gel Kits are small, so they can be taken with you anywhere and are very easy to add inside soft boxes, inside reflectors, over or under grids and even in connection with umbrellas (with the B1 series lights).

 

No where are gels more obviously important than in the right and wrong scenario of dealing with the ugly nature of florescent light. But remember that the entire world of light bulbs is changing. The color of an LED lightbulb can be changed via an iPhone at the drop of a hat. CFLs are rated as “soft white” at 2700 K and as “daylight balanced” at 5500 K in the isle of your local grocery store. So you can’t make any assumptions anymore. It is best to have a full compliment of gels for every light in your portrait kit. This way, you can correct for anything a location throws at you. Just be prepared with the right equipment and an understanding of the color of light.

Location: The Arizona Railway Museum, Chandler, Arizona

The gear

2 x B1 Off-Camera Flash
1 x B2 Off-Camera Flash
1 x OCF Softbox with Softgrid
1 x OCF Color Gel Starter Kit
1 x Air Remote TTL-C

作者: Jared Platt