Use of Whi-bal as gray card, Good or bad idea?

[kgphoto]

In a discussion on another forum as to whether or not using a Whi-bal as a replacement gray card would be a good idea, I had this thought. What do you think?

I have been thinking, that this idea is somewhat skewed.

While you could use the Whi-Bal as a density reference, to use it as a replacement gray card probably is not a good idea. Here is why.

An incident light meter is calibrated to return 18%(+/- company parameters, some say 12-15%). So if you use an incident meter for some readings and the Whi-Bal for reflected readings, you will have to compensate between them.

It is probably better, after calibrating your camera and lens combo and your light meter to give proper exposure, to take a reading of the Whi-Bal and compare it to the luminosity values in PS for a best exposed image and then you can use that value for the luminosity for the Whi-bal as a comparison point for future images. If the value is different in future images, by bringing up or down to your target value, it would bring the rest of the exposure in line.

Of course, this only applies if the Whi-Bal is in the mainly lit area of your photo and not in a shadow or highlight or experiencing glare.

All in all, perhaps it is just better to properly calibrate your meter to your camera and use that instead. This way you can use the incident reading for the average and the reflected for the range of exposure of the scene to see what needs to be modified or sacrificed.

[R_Fredrick_Smith]

The primary usage of the Whibal card is for setting your White Balance. It is usually not used for exposure determination. If you are interested in exposure determination using a target of some sort, then you might want to research the many threads on G1 about the use of the Photovision Black/Gray/White target (the one I use).

Re: Use of Whi-bal as gray card, Good or bad idea? 

cheers,
rfs