Saturday, December 6, 2008

Holiday Break

With this being such a busy time of year we will have a short holiday break. Check the right hand side of the screen to find your next Monday Post.

As always, feel free to post a new blog entry if you have a question or need help or have something neat to share.

Also, we would love to have others join us! You may have been using a camera for 70 years or 7 days, we still would love to have you join us. Post do not necessarily need to be tutorials. You can ask a question, present a challenge, ask for critique, or submit a picture and ask everyone to photoshop it to see the different ways people approach a photo. Lots of possibilities, get out of your comfort zone and join us =)

Monday, December 1, 2008

My color has a temperature!

As it turns out, all color has a temperature - measured in degrees kelvin, whatever that is!

The kelvin system of temperature measurement is very much like the celcius system, but it starts with zero at absolute zero instead of -273.15°C.

Right about now you're probably wondering what this has to with photography, aren't you? The short answer is...nothing at the low end of the scale. However, color temperature is a characteristic of visible light and is measured in degrees kelvin, which makes it important to know a little about it. Both the amount of light and the color temperature affect how the image appears in the finished product.

I know it's counter intuitive, but the hotter the temperature of a color, the cooler it is considered to be.

Color Temperature image taken from Wikipedia
The reason is because the color is approaching the green-blue end of the visible light spectrum. In the other hand, cooler color temperatures are considered to be hotter since they are approaching the yellow-red end of the visible light spectrum - thinking warmer here might help. Take a look at the CIE 1931 x,y chromaticity space in the image to the right. What you see here is the color spectrum from ultra-violet (very high °K) to infrared (much lower °K).

The table below gives a pretty good idea of the color temperature for a variety of different light sources:

Temperature Source
1700 °K Match flame
1850 °K Candle flame
2800–3300 °K Incandescent light bulb
3350 °K Studio "CP" light
3400 °K Studio lamps, photofloods, etc.
4100 °KMoonlight, xenon arc lamp
5000 K Horizon daylight
5500–6000 °K Typical daylight, electronic flash
6500 °K Daylight, overcast
9300 K CRT screen
Note: These temperatures are merely approximations; considerable variation may be present.

As you can see from the table, all of the sources are actually hot: flame, incandescents, the sun, etc. However, there is a conversion system that give you some idea of the color temperature of fluorescent bulbs called the correlated color temperature (CCT), which has to do with the perceived color of the blah, blah, blah. Here is more than you ever wanted to know about color temperature.

Now for a bit of setup information. I went to Home Depot an bought some metal reflectors and fluorescent bulbs. The bulbs are not very expensive, even though it says $77 dollars in the pictures (that's actually the savings over using an incandescent bulb). The prices were about $4 for two of the bulbs and $6 for the third one. However, if you want, you can go to B&H's web site and pay a couple hundred buck if you want...

I used a peninsula cabinet for the setup. First, I draped a roll of kraft paper over a box to create a cove. (A cove is just a way to get a nice smooth corner as a backdrop for your subject. The principle is the same if you are shooting people or things.) Next, I clamped the reflector to one of my old tripods and mounted the camera on the good tripod. I placed an 18% gray card on the cove (as a reference) and placed the subject on the card. That pretty much tells the whole setup story, so check out the picture below to see what I'm talking about.

Then I took a series of pictures - two with each bulb. The first image is always with the light source to the left. The second image always uses a reflector to fill in the light on the right (move the reflector around until you can see the subject being filled with a reflection of the light source in the left).

This first set of picture uses the Daylight bulb. I estimate the color temperature to be around 6000K, or the daylight range. Notice how realistic the images look - almost as though they were taken outside. Also notice the second image with the light filled in on the right as the light source is reflected back on to the subject.

f/4.0, 1/40, iso400, AE, 18.0mm Focal lengthf/4.5, 1/50, iso400, AE, 18.0mm focal length

This next set of images uses the Bright White bulb. Here, I estimate a color temperature of about 4500K, or the moonlight/Horizon daylight range - early sunset type of lighting. Now you see the image start to approach the yellow end of the spectrum.

f/4.5, 1/20, iso400, AE, 18.0mm Focal lengthf/4.5, 1/25, iso400, AE, 18.0mm focal length

Lastly, the Soft White bulb supplies the light. I'm guessing somewhere around 3300K, which is something like using available light in your living room. Notice how warm the images have become as the light source approaches the yellow end of the visible light spectrum even more. Also, the farther you are from your light source the warmer the picture will be. The reason is simple physics - a little principle they all the inverse-square law. All you really need to know about this inverse-square law is an object twice as far away from the source, receives only ¼ the light energy. And here is more than you ever wanted to know about the inverse-square law.

f/4.5, 1/25, iso400, AE, 18.0mm Focal lengthf/4.5, 1/30, iso400, AE, 18.0mm focal length

The three lighting situations simulated here are bright sunlight where the sun is primarily over head, early evening and available light inside the house. I tried to keep the camera pretty much at the same settings, even though the shutter speed did vary a bit.

That's pretty much it. Now that you got a basic understanding (and I do mean basic), give it a try. Select your lighting condition and start shooting. I'm looking forward to seeing what you come up with.