white balance and grey card

how do i use a grey card properly with my s2, i shoot a lot in "p" mode

For WB; set WB to "Custom", aim the camera at the grey card, press "Menu" again and it's memorized. Should be explained at greater length in the "White Balance" section of your manual. But once you set a Custom White Balance, that is what will be used in Custom until you undo it.

Hmmm - is that a trick question !

You should use a "white card" to set a custom white balance, the grey card is used for setting exposure. Most of these cards such as the Kodak ones, are double sided, use the white side to set your white balance then turn it over and measure the exposure.

removed

In fact Canon recommends using a grey, not a white, card for setting white balance, since "correctly exposing" a white card may blow one or more colour channels, throwing off your CWB setting.

Don't know about the S2 but my A95 manual says "a piece of white paper or cloth, or a photo-quality gray card". I would think that applies to other Canons as well.

I've found that white paper or a handkerchief works just fine but in any case it's easy these days to make minor corrections to the color balance later when processing.

In the EOS models they say "Instead of a white object, an 18% gray card (available commercially) can produce a more accurate white balance."

You can use any neutral surface to set white balance - the key word being neutral. Generally an 18% reflectance grey card is used for measing exposure and the white reverse from manufacturers such as Kodak for determining White Balance because this is more neutral. In practice the difference may be so slight it may not matter.

The white reverse side of a good 18% grey card is not "more neutral" than the grey side. Both are neutral. Either can be used; the danger with white is that you might blow out the channels.

OK - should have done this in the first place

Quoting from my Canon EOS 5D instruction manual

"With custom white balance, you shoot a white object that will serve as the basis for the white balance setting"

Then in small print down the bottom it says

"Instead of a white object, an 18% grey card can produce a more accurate result"

So as Jon says - I got it wrong - sorry- all those years of flipping the card over were not neccessary.

Well I thought I was following the instructions that came with the card Jon - should have read the camera manual more closely - took your mention to make me go and dig it out.

The 90% white side's offered for exposure metering in low light conditions or for use with a color balancing meter. It's a legacy of film.