White balance

[girishmenon]

<p>Technically, do diffusers and flash modifiers alter the white balance of a flash?<br>

For example, if I fire the flash without any diffuser, then the same flash with a bulb diffuser, and finally if I shoot it through a white umbrella, must the white balance (color temperature, tint) in each of the images be different?</p>

[Ed_Ingold]

<p>Diffusers can certainly have a color caste, including alterations of infrared and ultraviolet light which affects color balance. They also tend to spill light into the room. Reflections of that light affect the color balance. Finally, the color of the flash itself may change depending on its settings. You pay big bucks for flash units that maintain a (relatively) constant color with varying power. If color balance is critical, control the color of the room (white, black or neutral gray), or minimize the amount of spill relative to the direct light.</p>

<p>I'm not a commercial photographer with a controlled environment, so in my view, it's better to be consistent than perfect. For many things, color balance may not be critical as long as it falls within subjective limits. A diffusion dome on the the camera's flash bounces light from all surfaces in a small to medium sized room, making the light relatively even and "natural" for candids. Precise color balance is, obviously, uncontrolled, but usually acceptable or at least consistent, hence easier to correct in post.</p>

[craig_shearman1]

<p>"do diffusers and flash modifiers alter the white balance of a flash?"<br /><br />The short answer is no.<br /><br />Most umbrellas, softboxes, plastic diffusers that snap onto the flash, etc., are intended to be color-neutral and should not affect white balance. Some are more perfectly neutral than others. But for the most part they are neutral, certainly to the point that you are unlikely to see the difference in your photos.<br /><br />Units that bounce the flash can, of course, pick up the color of whatever wall or ceiling the light is bouncing off of. But that's from the wall/ceiling, not the light modifier itself.<br /><br />There are modifiers that do intentionally change the white balance. The StoFen Omnibounce, for example, is available in the standard neutral version but also an 85B version that matches the flash to tungsten light so you can use you your flash as fill light when shootning under hot lights. It's aimed largely at news photographers shooting alongside TV crews. They also make a greenish version to balance with fluorescent lights. You can get some umbrellas in colors -- I think Lowel used to make a blue umbrella to balance its tungsten hot lights to daylight.<br /><br />For what it's worth, I think photographers in the digital age obsess too much over white balance and get taken advantage of by companies sell all sorts of white balance gadgets. In film days, there was daylight film and tungsten film. Daylight covered all daylight situations and flash, and tungsten covered hot lights. That was it. If you were shooting under fluorescent, there were correcting filters you could use. Sodium or mercury lights you pretty much prayed and tried to correct the color when you made prints. But unless you were shooting something where color was absolutely critical -- like making sure the Kodak yellow on a film box came out Kodak yellow and not canary yellow or taxicab yellow -- you didn't worry much about being off a hair.</p>

[Matthew Currie]

<p>I tend to agree with Craig in general, but would add that the one diffuser I've used recently, which was one of those little white screens that clips in front of a built in flash, does indeed alter the white balance noticeably.</p>

[ellis_vener_photography]

"Technically, do diffusers and flash modifiers alter the white balance of a flash?"

 

Yes they do. Mostly by absorbing some of the ultraviolet and higher frequencies of the blue component of the light.

 

You can test this for yourself.

 

Like setting color space and "camera style" on your camera, "White balance" is a bit of an artificial construct for raw

digital photographic files. Any setting of the three on your camera are essentially only suggestions for how you want the

basic photo to appear and can be changed by any decent raw processing program.

 

Adobe's raw processing program is called Adobe Camera Raw and its the same engine under a different hood in

Lightroom. For setting "white balance" is a combination of setting the relative balance between yellow to blue (Color

Temperature expressed in Kelvin degrees) and green and magenta ("Tint")

 

Now if you take into account the Exposure control, these three controls start looking awfully like a way to work in the LAB

color space. (at least one Adobe engineer who really and truly knows the ins and outs of the ACR color algorithms

agrees with me on this.)

[rodeo_joe1]

<p>+1 to Matt and Ellis's responses. Nearly every white diffuser/softbox/umbrella I've ever used has warmed the light output a little - never cooled it. Nearest you'll get to neutral is a silver umbrella, but the nasty ripply light they give makes me avoid the use of them if possible.</p>

<p>Besides, the use of a custom balance should be a matter of course for any studio work. It only takes a few seconds and a folded sheet of white A4 copy paper.</p>