7D and WB calibration with 18% gray card

The idea of the original Expodisc was that it converted your camera's TTL meter to an incident meter, so you used it that way, placed it at the subject's location, pointed toward the primary light source.

SkipD wrote in post #9729757
Where do you point the camera with the Expodisc on it for this? Where is the camera during this relative to where you'd make the image from? I ask this because for white balance, you're supposed to aim the rig at the light source(s).

skip i think your missing this a little. forget the expodisc. you shoot the photovision card just like you would use a 18% grey card and set the photovision disc as your source for custom white balance. then you can go to your histogram and see where your shadow,mids,and highlight lines up. want to get the mid right in the middle,,then adjust aperature so the highlight pushes slightly left w/o clipping. images will be beautiful.

slowdad wrote in post #9729862
skip i think your missing this a little. forget the expodisc. you shoot the photovision card just like you would use a 18% grey card and set the photovision disc as your source for custom white balance. then you can go to your histogram and see where your shadow,mids,and highlight lines up. want to get the mid right in the middle,,then adjust aperature so the highlight pushes slightly left w/o clipping. images will be beautiful.

OK. After clicking on the link in your first post of this series, I understand. However, your post (#11) was answering someone who was writing about the Expodisk, and your term "Photovision disk" seemed like it was an Expodisk clone you were referring to. That is the source of my misunderstanding.

Pearlallica wrote in post #9727671
Just hold the card directly under light source, turn off auto focus, (use auto WB setting) take the shot and select the image as your custom white bal reference.

Is the card supposed to be out of focus?

slowdad wrote in post #9726644
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Looks like a good product for exposure control. But is it spectrally neutral so it can be used accurately for white balance? I don't see anything on their website claiming it's spectrally neutral, so I'm not sure how consistent their products are.

The WhiBal looks like a good product and seems to have strict tolerances, but that's only for white balancing. If the Photovision is spectrally neutral and is manufactured to strict tolerances like the Whitbal, then that's even better since it can do exposure and white balancing.

Positive review for white balance lens cap solution.

http://www.inlightinwo​rkshop.com/tag/article​/

solara wrote in post #9859097
Looks like a good product for exposure control. But is it spectrally neutral so it can be used accurately for white balance? I don't see anything on their website claiming it's spectrally neutral, so I'm not sure how consistent their products are.

The WhiBal looks like a good product and seems to have strict tolerances, but that's only for white balancing. If the Photovision is spectrally neutral and is manufactured to strict tolerances like the Whitbal, then that's even better since it can do exposure and white balancing.

i use the photovision disc and i also use an x-rite color checker. its 2 shots for perfect color and exposure. one for the exposure, one with the color checker below the chin. then all i have to do is open in lightroom, click the white balance and apply to the session.

Just a quick question about the "select white balance by eyedropper tool"-thing:

Is there any tool to select more than ONE pixel for doing that in the RAW converter of your choice? I'm asking because if you have something like the 50D (I'm currently using one) and you have to deal with medium noise even at lower ISO settings, the chance that you will select a "noisy pixel" instead of a "clear grey pixel" is really high! It would be much better to select something like 30x30 pixel and take the average "white balance value" of them. Any solutions?

Best regards,
Hendrik

SkipD wrote in post #9730499
OK. After clicking on the link in your first post of this series, I understand. However, your post (#11) was answering someone who was writing about the Expodisk, and your term "Photovision disk" seemed like it was an Expodisk clone you were referring to. That is the source of my misunderstanding.

You can still use the expo disc for exposure. It is supposed to only let 18% light through. You point your camera from the position of your subject back to where you are shooting and your cameras meter will meter for 18%.

I find it's a handy tool. I found it way too expensive for what it is, but I do use it all the time to set a custom white balance in camera, even if I shoot raw.

You can also use it to check for dust, and vignetting since it's just a blank image.

Hendrik C. wrote in post #9861106
Just a quick question about the "select white balance by eyedropper tool"-thing:

Is there any tool to select more than ONE pixel for doing that in the RAW converter of your choice? I'm asking because if you have something like the 50D (I'm currently using one) and you have to deal with medium noise even at lower ISO settings, the chance that you will select a "noisy pixel" instead of a "clear grey pixel" is really high! It would be much better to select something like 30x30 pixel and take the average "white balance value" of them. Any solutions?

Best regards,
Hendrik

Just click around a few times to be sure you're getting one that looks right. The WB eye dropper tool in the raw converter is about as non-destructive as it gets.

Still a very good question and one that raises an important point that many people overlook.

Hendrik C. wrote in post #9861106
Just a quick question about the "select white balance by eyedropper tool"-thing:

Is there any tool to select more than ONE pixel for doing that in the RAW converter of your choice? I'm asking because if you have something like the 50D (I'm currently using one) and you have to deal with medium noise even at lower ISO settings, the chance that you will select a "noisy pixel" instead of a "clear grey pixel" is really high! It would be much better to select something like 30x30 pixel and take the average "white balance value" of them. Any solutions?

Best regards,
Hendrik

The software guys have ALL missed the point, with their WB tools not being able to select an area and compute the mean value for that area!

Well... that just sucks!

Could someone tell me the process of setting a custom WB using the photovision card? I'm new to the Canon system and having problems getting a proper WB setting using it. Please help!

ERP wrote in post #9865039
Could someone tell me the process of setting a custom WB using the photovision card? I'm new to the Canon system and having problems getting a proper WB setting using it. Please help!

BEFORE EXPOSURE: Take a picture of the PhotoVision with it filling the frame as much as possible (all three segments in the frame, black, gray, white), and use that exposure to set the custom WB in camera. (You do not have to fill the frame, but then you have to have determined how little of the frame has to be filled yet still render accuracy in WB) Or, you can fix in postprocessing...

POSTPROCESSING: Take a picture of the PhotoVision, use the postprocessing WB tool and click on the center (18%) gray area.

I don't think I missed this in the thread but a primary reason for using a grey card for white balance is because your everyday "white" papers and card may contain brighteners. These are fluorescent compounds and tend to be quite blue.

Cheers, Ray.