10.16.2017

Kirk's Photography Tip of the Day. CWB. (Custom White Balance).

42.5

I was setting up to shoot in a conference room downtown this morning. I had an hour to put together the lighting and design of the shot and used myself, as a halfway willing model, to stand in. The conference room is lit with a bunch of different light sources as well as a wall of frosted, tinted glass windows. I used an LED panel, shining through a 50 inch, round diffusion panel to the left of the frame and a silver bounce reflector about ten feet back on the right. I also added some LED panels with warming filters to the back plane.

With all this light bouncing around I knew I wanted to do a custom white balance. I set up a gray target and made a white balance while using the Panasonic 42.5mm f1.7. As I continued setting up I tried several different lenses to see what the cropping would look like with a 50mm and a 40mm focal length. When I switched from the 42.5mm to the 40mm I was surprised at the difference in color between the two lenses. Nothing else was changed and both lenses were stopped down to equal apertures, yielding exactly the same exposures, as measured by the GH5's internal waveform monitor.

The older lens, the 40mm, was much warmer and stumbled into a slight yellow cast. Using the same white balance target and re-setting the color balance brought the two lenses much closer in final color. The third lens had a slightly cool, or blue, tendency compared to the modern Panasonic. It too could be made to get close to the 42.5's color when custom white balance. Without the custom white balances the images created by each lens were quite different.

This reminded me that for precise work a custom white balance actually needs to be done between lens changes. It was a sobering reminder that some of what we do is more of an art (or craft) than a science.

While I am not a good portrait subject my client this morning was. I was delighted with what I finally came up with as a lighting design for her. I think I'll work harder at staying behind the camera.....

Working with precision? Did you know different color balances also change exposure? New rule: New lens on the scene? Custom white balance and create a channel for that particular lens. It's a good way to eliminate the need for color matching between files in post.

The lenses, used on a GH5, were: the Panasonic 42.5mm f1.7 (the nicest WB in AWB), the Pen FT 40mm f1.4 (the least accurate, color wise) and the Zeiss 50mm f1.7 (Best tonality, middle of the road color accuracy).

It's fun to experiment. Sometimes I learn stuff...

14 comments:

MO said...

yeah it can be a mess when You try to mix lenses in a movie production. another time when i have a even harder time is when the sun sets and the windows brings a part of the lightning. thats almost impossible. thanks for the tip ;)

rexdeaver said...

I love the 42.5 f1.7. I use it exclusively for my social media portraits.

Phil Stiles said...

"It was a sobering reminder that some of what we do is more of an art (or craft) than a science." I had the opposite reaction: that there's a lot of science in this aspect of the craft. Setting a white balance, or creating a custom color profile for a lens seems very much science. Placing lights for a pleasing modeling effect, now that's an art. Nonetheless, a great tip, especially for those of shooting with a variety of lenses.

Kirk Tuck said...

Phil, I guess what I was thinking is that we come to things like lenses more or less expecting them to be "transparent" in terms of color. I'm not sure people really consider color variations when they research lenses. But the color is part of the look and many times the total look defies a scientific analysis. I agree that setting the WB is a technical thing but someone else has done the science. We're still making art choices. Do we modify the CWB by shading the hue in one direction or another? Do we shift the color temp to match a vision. There are very few parameters on cameras+lens systems that I consider defaulting to the "science" and leaving them in default. The process may be science but the tweaks are mostly subjective and that makes them art, in my mind. But I have found one thing, I can control color to a greater degree now that I have a vector scope in camera (and on my Atomos).

Anonymous said...

Kirk

Noob question. What is a waveform monitor and how does it assist you in obtaining a custom white balance? Thanks in advance.

Jay

Kirk Tuck said...

Jay, the waveform monitor is a graphic representation of exposure across a frame. I use the waveform monitor to set exposure. If I point a camera at a gray target and change exposure until the target "reads" at 50% (plus or minus five) I know I have the right exposure for my shot based on the position of gray in the middle zone. The tool that aids in establishing white balance is really the vector scope which can show how accurately fleshtones are reproduced and where the colors fall with a particular balance. Are they accurate or off? The vector scope can show those relationships. I'll write up a better explanation tomorrow.

David said...

Lenses definitely have color. I shoot jewelry for my wife's Etsy site, mostly with an Olympus 60mm macro. But for big pieces, I sometimes have to switch to a 25mm lens. If I don't do a white balance after the lens swap, the image colors don't match.

Kurt Friis Hansen said...

Ehhh...

CBW? Not explained! So: Ehhh... I can guess, but how do I know, if I'm right?

Let's see:

http://www.cwb.gov.tw/V7/index.htm
http://cbw.dk
https://en.wikipedia.org/wiki/CBW

and on and on and on and... including links to real nasties ;-)

I really, really didn't know, that Canterbury West railway station in the near(er)by UK, had the station code "CBW". You never know, when you'll learn something new - probably not that useful, alas... still new knowledge to commit to short term memory.

Why not explain "forkortelser" - sorry: "abbreviations" - when used? It makes life easier for everyone. Also foreigners and beginners into photography.

Smile

Gato said...

Interesting stuff. I've known lenses have different color rendition -- I've heard it as an argument for sticking to one brand -- but for some reason never thought about doing separate white balances.

I'm looking forward to your write-up on the vector scope -- I tried Google when you mentioned it before and learned a little, but it will be interesting to see how you use it on the job.

Kirk Tuck said...

Sorry Kurt. CWB= Custom White Balance.

JerseyT said...

Interesting post. I'm surprised that lenses exhibit that much of a color bias.
I think you confused a few people though. It looks like you were setting up for
a still photo session, but you mentioned video instruments - waveform monitor
and vector scope (in a comment).
The waveform monitor can help set exposure rather than a histogram, but how do
you use the vector scope? Do you have a color target in addition to the gray
target?

Steven Willard said...

I second Rex’s comment about the 42.5. A great lens, under appreciated, that punches above its price and weight class. Compact, sharp even wide open, fast to focus and quiet. What more could one ask for?

Kirk Tuck said...

Jersey T. Go to the video mode, use waveform to set exposure. Use vector scope, filling the frame with your subject's face and then modify WB to hit the "flesh color" target line on the vector scope. Alternately, substitute a color target for your subject and see how close you can get to each of the color indices. Nothing like it in still cameras. Just more control.

RGM said...

What do you mean by creating a channel for a specific lens, is that a GH5/ Atomos feature?

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