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ExpoDisc and the I2 camera.

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Just for fun, I got one of these ExpoDisc things ( Amazon.com : ExpoImaging ExpoDisc 77mm Digital White Balance Filter - Neutral : Camera Lens Color Correction And Compensation Filters : Camera & Photo ) for my DSLR out of its bag. Thought I'd try it on the X4S camera for fun.

I rubber-banded it to a 1" thick stick so it would be centered in front of the lens about 1/4 inch after it was turned on and centered. Pointed the entire affair towards the sun.

Turned on the Color Waveform screen in Camera Settings as well as the Histogram.

Moving the Exposure to center the white spike off the ExpoDisc in the middle of the Histogram, in the color Waveform window I could see the Red, Green, and Blue bars alone the entire width of that window. By sliding the White Balance Slider in the Camera I could eventually overlap all three of them to a white line instead of the colors. What number below the slider is the white balance for that light source.

I got 4,900K to even mine. When I clicked it through Auto, Sunlight, Cloudy, Incandescent, Fluorescent I could see the bars separating or moving together. Auto takes a couple of seconds to zero out to a white bar.

When I turned the affair 180 degrees away from the sun, the bars meshed to white at around 6,900K.

Usually I leave it set to 5,200K and fly it.
 
Just for fun, I got one of these ExpoDisc things ( Amazon.com : ExpoImaging ExpoDisc 77mm Digital White Balance Filter - Neutral : Camera Lens Color Correction And Compensation Filters : Camera & Photo ) for my DSLR out of its bag. Thought I'd try it on the X4S camera for fun.

I rubber-banded it to a 1" thick stick so it would be centered in front of the lens about 1/4 inch after it was turned on and centered. Pointed the entire affair towards the sun.

Turned on the Color Waveform screen in Camera Settings as well as the Histogram.

Moving the Exposure to center the white spike off the ExpoDisc in the middle of the Histogram, in the color Waveform window I could see the Red, Green, and Blue bars alone the entire width of that window. By sliding the White Balance Slider in the Camera I could eventually overlap all three of them to a white line instead of the colors. What number below the slider is the white balance for that light source.

I got 4,900K to even mine. When I clicked it through Auto, Sunlight, Cloudy, Incandescent, Fluorescent I could see the bars separating or moving together. Auto takes a couple of seconds to zero out to a white bar.

When I turned the affair 180 degrees away from the sun, the bars meshed to white at around 6,900K.

Usually I leave it set to 5,200K and fly it.
Unfortunately they are not that great since they only allow setting the WB by measuring the light falling on the filter (which is screwed to the lens). Since the temperature of this light is invariably different to the color temp of the light reflected from the subject (which is what you actually want to measure) this renders this gimmick pretty useless.
 
Unfortunately they are not that great since they only allow setting the WB by measuring the light falling on the filter (which is screwed to the lens). Since the temperature of this light is invariably different to the color temp of the light reflected from the subject (which is what you actually want to measure) this renders this gimmick pretty useless.
Sorry, but you are so wrong.

Ever use an incident light meter? A color temperature meter? Both point TOWARDS the light source in use. The light falling on the subject is what sets the color temperature, not the light reflected from the subject. Both instruments are reading through and towards the light source through what is basically the ExpoDisc filter.

Fwiw, I own a Sekonic Prodigi Color C-500 Color Meter and my little ExpoDisc adventure coincides with its readings too when gathering the light coming from the source. So if one doesn't want to shell out for a Sekonic, the ExpoDisc is a cheap way to find out what the color temperature is. Plus you can actually see the RGB curves in GO 4 and how they overlap coming off the sensor should it be off.
 
Sorry, but you are so wrong.

Ever use an incident light meter? A color temperature meter? Both point TOWARDS the light source in use. The light falling on the subject is what sets the color temperature, not the light reflected from the subject. Both instruments are reading through and towards the light source through what is basically the ExpoDisc filter.

Fwiw, I own a Sekonic Prodigi Color C-500 Color Meter and my little ExpoDisc adventure coincides with its readings too when gathering the light coming from the source. So if one doesn't want to shell out for a Sekonic, the ExpoDisc is a cheap way to find out what the color temperature is. Plus you can actually see the RGB curves in GO 4 and how they overlap coming off the sensor should it be off.
And where do you hold your light meter?
Next to your subject - You don't hold your light meter next to your lens do you?
You want to measure the temp of the light falling on your scene not what is falling on the front element of your lens.
 
And where do you hold your light meter?
Next to your subject - You don't hold your light meter next to your lens do you?
You want to measure the temp of the light falling on your scene not what is falling on the front element of your lens.

That's what the ExpoDisc and/or a color temperature meter are doing from the subject position pointing at the light source. I'm lost as to what you are thinking, but I think we are in agreement of WB being from the source and pointing at it to read it.

This is old, but pretty much shows the ExpoDisc in use reading towards the light source:

I could have pointed my color temp. meter at the same source and got the reading too, just it cost me $1,200 for it.

Both are tools, just one is cheaper and a bit more cumbersome and slower to use. Still watching the three color bars fall into a white band is sort of cool on GO 4's Color Waveform screen when you nail the WB setting with the ExpoDisc. You can also see the gray color shift when the red bar rises and makes the gray reddish in the waveform if the WB is wrong. Plus you are seeing it off the camera sensor which may not agree with an external meter or DJI's setting. My drone seems to like to be a bit warmer than what the Sekonic meter shows to pull it into a solid white band off the ExpoDisc.
 
Unfortunately they are not that great since they only allow setting the WB by measuring the light falling on the filter (which is screwed to the lens). Since the temperature of this light is invariably different to the color temp of the light reflected from the subject (which is what you actually want to measure) this renders this gimmick pretty useless.
By the text that's in bold, Casey is 100% correct. However, I think Editor intended to indicate WHERE the meter is actually held during the moment of measurement. With only about 35 years as a professional photographer (including having been a photo magazine editor), I think that I know this subject pretty fluently.

To measure the color temperature, your meter should measure the light as it reaches your subject, not off your subject. Often that might be identical to what would reach the photographer/camera, especially if Mother Nature is the light source. In a studio, you'd definitely measure at the subject and NOT at the camera.

In my experience, the ExpoDisc had more value in turning any scene into a neutral 18% gray exposure. I'd never use one to measure the color balance of a scene by placing it in front of my lens.
Think what would happen if you did that same technique with a red wall and a yellow wall, both filling the lens' normal view. You'd get two totally different K˚ measurements. Even using the ExpoDisc to measure a white wall and a black wall would be off. The disc would try to turn both into an 18% gray, grossly different from the original white or black subjects. However, using an INCIDENT meter that measures the light directly, before it hits the subject, would yield accurate and repeatable results.
 

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