Wednesday, May 18, 2011

Flash Series - Part 2: Home Made (DIY) Gels & Gel Holder


In this second part of the flash series (here's the first one) I will discuss home made gels and how do they perform in the real world, I might get a little philosophical (i.e. non-scientific) during the article, so please excuse me. Hit the jump for details and a bonus gel holder idea.

P.S. I wrote an introduction to white balance and color temperatures, but I found it to be too long, thus I have moved it to the bottom of the post, if you don't know what is a color temperature, read the bottom part first.

When I started my strobist path, I was hit in the face with the complete lack of gels in the photography shops in Egypt, and since I don't have a way to order and ship things from US (I do now, but it is expensive, so I leave it for urgent stuff) I had to look for DIY gel solutions, and after some looking around I found this amazing page where I downloaded my gel PDFs and was able to print them and use them. If you're living in the US you can get the ready made Rosco Strobist Gel Set for $9 instead.

The idea is that you have a PDF file with the main gel colors on it (you can make your own if you want), then you buy a laser transparency sheet and print these PDFs using a color laser printer, now you have a sheet with your gels ready, just cut them and find a way to put them in front of your flash head and you're ready to go. You can see my own set at the top of the post.

As far as endurance and heat resistance goes, I never had a problem in that regard. The laser transparencies I used are designed to handle the continuous heat from projector bulbs for extended periods of time, and although I have printed more than one sheet, I am still using the first one I printed.

DIY GELS SYNTHETIC TEST RESULTS

I have never used a real commercial gel on my flash, so I have no idea how they should perform. First, let me talk about tungsten white balance, there is no exact color temperature for tungsten, it depends heavily on the type of the bulb used and the furniture/walls the light reflects from. For example in my room the tungsten WB is around ~ 2200K, while in a different room in the house it is ~ 2650K, and my Canon camera considers tungsten WB to be 3200K, and lightroom has a different temperature!!!


So in order to determine what's what, I used my digital grey kard and tested the color temperatures in different lighting scenarios, my method involved shooting the grey card in RAW then importing the photos to lightroom and using the dropper to select the grey card and determine the correct white balance, here's what I found out:
  • Available light only (tungsten): 2650K
  • Direct flash with full CTO (zero ambient): 4500K
  • Bounce flash with full CTO (zero ambient): 4000K
As you can see, the full CTO doesn't bring the flash color temperature anywhere near the tungsten WB, so does this mean that they don't work? Let's see. Will the Rosco full CTO bring the flash WB to 2800K? I don't know, and if anyone can test this, please do and tell me.

DIY GELS REAL WORLD TEST RESULTS

In this part I will show you how these gels work for me in real life, then I will try to explain the results. When I finished shooting the pictures for this test I discovered that my camera was set on JPEG only and it was impossible for me to re-shoot the pictures or adjust the WB in post, fortunately enough I had the mind to set the WB to tungsten.

Available Light Only

Available Light + Bounce Flash (no gel), do you see the blue color cast?

Available Light + Bounce Flash (1/2 CTO), blue color cast still visible

Available Light + Bounce Flash (full CTO), a much better result


MY PHILOSOPHY:

I think the results speak about themselves, here's my own explanation (philosophy), first of all there is no certain defined white balance for each type of bulb or lighting, the light your camera picks comes from different sources, there is the direct light coming from the source hitting your subject, and there are a lot of other indirect reflections coming from lots of objects around your subject (ex. walls and furniture), these two reasons cause the color temperature to change from one place to another, even from a different position in the same room to another.

When you add bounce flash to the equation, you add a new non-controlled dimension, your flash will bounce from different surfaces and carry different color casts from these surfaces and will probably give you unexpected results. What's more is that when using bounce flash, one usually underexposes the ambient light by one or more stops, thus rendering the original ambient colors muted that it won't really have an apparent effect in the final picture.

Add to all of this the bless of using RAW files and the ability to change the white balance in post at will, and you have a pretty good way to get the results you desire. I almost always tweak the white balance in post processing and adjust it for the correct skin tones (you can use a digital card for a quick and easy adjustment), this adjustment won't have much effect on the rest of the picture (ambient lit) and even if it does, the ambient is already underexposed (muted) that it won't look bad.

In some rare situations when using bounce flash I get some strange color casts that I can't get rid of, my solution is to pull the saturation slider all the way to the left and have an artsy black and white picture.


DIY GEL HOLDER:

To continue with the DIY theme, I have made my own gel envelope (to carry the gels in) and a gel holder to mount the gels to the flash, I saw lots of different ones on the internet and I didn't like most of them, especially the velcro ones since it required me to stick velcro to my flash (which I didn't want to do back then) and will make me stick velcro to each and every gel, then in one of those brain-light moments I had the following idea.

I created a gel holder from the exact same transparency sheets that I used for printing gels, I cut it to size then bent it and pressed that bend with a ruler edge. To mount the gel holder to the flash I pull the diffuser slightly then insert the gel holder and push it with the diffuser, I think the pictures will explain it better.

This is an envelope created from cardboard to carry my gels in

DIY Gel Holder

DIY Gel Holder

Inserting the Gel Holder

Ready and Firing

This article took me a long time to write, so I hope it has been beneficial to you and I am ready to answer any questions you have. My next post will be a break from the flash series where I will discuss RAW vs JPEG, you wouldn't want to miss it. :-) 

__________________________________________________________________________________

INTRODUCTION TO WHITE BALANCE AND COLOR TEMPERATURES
 As you probably already know, each light source has a different color temperature, tungsten bulbs for example have a warm (more orange) color cast while the day light has a more cooler (more bluish) color temperature. Color temperatures are expressed in Kelvin, so for tungsten lights, the color temperature revolves around 2800K, while for day light it is more like 5200K.

What does this have to do with white balance? Imagine you have a white piece of paper and you're sitting in a room with tungsten lighting, when you take a picture with your camera the paper should look white, now if you take the same picture in a fluorescent lit room, the paper should still look white, are you getting my drift?

The white balance is the way you tell the camera that you are shooting in a certain light temperature, so it can correct the colors in the picture accordingly, otherwise the picture will have all the wrong colors, maybe with an orange tint, maybe with a blue color cast, so setting the correct white balance on the camera is very important to get correct looking skin tones.

SO WHAT DOES THIS HAVE TO DO WITH GELS?

Now you understand that when you're shooting in tungsten light you have to set your white balance to tungsten and so on, now imagine that you are using the flash in this same tungsten lit room, your picture would have a mix of warm color (tungsten ~ 2800K) and a cool color (flash ~ 5600K), it will look ugly with two color tones like many of the party pictures you see on facebook.

The solution to this is to change the color temperature of your flash to match the main light source (tungsten in our example), it is easier this way since you probably can't change the color temperature of your light source, the other reason is because the flash's color temperature is sort of neutral (white) where you can make it more warm or more cool by adding gels.

One of the very famous gels is the CTO gel, which is short for "Change To Orange", i.e. you will make the flash's color temperature warmer and closer to tungsten light, this way you can set your white balance to tungsten and use both the room light and the flash together without any strange color casts. Another less famous gel color is the CTS (Change To Straw) which is used by Neil VN, this one also changes the flash color temperature close to tungsten. There are a whole lot of gels like 1/2 CTO (less warm than full CTO) and CTG (changes flash temperature to match fluorescent light), and even other colors that can be used to have red or purple backgrounds or whatever, you are only limited by your imagination.

One final thing I want to mention before we dig into the gels is that a warm skin tone is usually preferred to a blue skin tone, that's why many photographers have a 1/4 or a 1/2 CTO gel on their main flash to get a slightly warmer skin tone even though they are only using flashes as their light source and don't have to color match something else.
__________________________________________________________________________________

RELATED POSTS:

Flash Series - Part 1: Canon Speedlites Chat (580EX II vs 580EX vs 430EX)