Panasonic GH5 Manual White Balance Questions

I am shooting a Panasonic GH5 for UW video and I have two somewhat naive questions about the manual white balance.  I was told that I should center the exposure meter before performing a manual white balance.  If I am shooting all manual I can do this.  However, I usually have my exposure at -2/3 of a stop when shooting video so this requires more fiddling.  I am not sure if centering the exposure meter makes any difference?  My next question concerns the card to use.  The usual wisdom is to use a grey card for the manual white balance.  Surprisingly though, the GH5 manual (pg. 110)  states "Place a white object such as a piece of paper within the frame at the center of the screen."  So I have been trying a white card versus a grey card.  I am not sure which works better and the goal is to avoid the dreaded magenta water colour.  Any advice would be appreciated.

Thanks

Stephen

A true white or grey card are actually the same colour, the grey just has lower reflectivity.   A camera meter will try to render a white piece of paper as 18% grey.  If you use a white piece of paper the camera will try to make it 18% grey - which is the colour/reflectivity of an 18 % photographic grey card.  I suspect the reason they want you to center the exposure is to get a strong signal to work from to determine the balance. 

I would just try it and see, if the white balance comes out acceptable just keep doing the same thing.   It sounds like you have been doing manual WB already.  Is there anything you don't like about the results so far?

What you say makes a lot of sense about white versus grey.  Also, if the exposure meter is too low then there would not be a good signal on which to perform a manual white balance.  I think I just need to be more careful when I am doing a manual white balance underwater.  Another issue is that when I am deeper than 20 meters, and there is low ambient light, the GH5 may be at its limit to do a reasonable manual white balance.

Thanks

You may want to browse my blog as I have covered pretty much any video topic since 2018

https://interceptor121.com/2019/09/24/the-importance-of-underwater-white-balance-with-the-panasonic-gh5/

A grey card is for exposure metering and is 50% IRE

A white balance card instead is 70% IRE 

They are not the same thing and it is not a good idea to white balance on a grey card

Thank you Interceptor121.  Your blog goes into great detail on filters, color profiles and LUTs for the GH5.  I have much to think about.

Regards,

Stephen