18 % Grey card histogram

[lejazzcat]

Hi all,
I recently bought a reference grey card so I have a question for those that have one.
Ive experimented by filling the image(viewfinder) with the card,spotmeter mode(so i dont really need to fill the viewfinder), f8, using even(overcast) daylight lighting (avoiding any shadows) and im rather surprised by the results .

the histogram rather than showing a perfect midway spike, rather shows a wider curve at around the 1/3 mark(midway within the 2nd quadrant down to black).
Seems the camera is seeing a gradual grey scale???

1/shouldnt it just be the single grey tone? i used the kit lens 18-70 for this, but the vingeting cant be that bad...
2/ why isnt it a perfect middle spike, why left of centre?

3/ is the spotmeter calibrated to 18% grey ?- or is it 16% like the sekonic spots? and hence always needs a 1/4-1/2 stop adjustment to be 'correct'?

4/ does this mean that i need to always use exposure compensation to correct this ?

TIA

[digitor]

This page explains all....

http://www.bythom.com/graycards.htm

Cheers

[lejazzcat]

Oops - i meant 12% grey for the sekonic spots - and thanks for that link !

[MHD]

Reading that link makes me very thankfull I shoot digital

[marcos]

After reading that link, something came to my mind from the seminar I attended on Digital Workflow yesterday. You can read my post about the seminar here

http://www.d70users.com/viewtopic.php?t=9742

The use of 18% gray card as a standard is owed o Kodak, they had to come up with that % to compensate the blue color cast from the its chip and metering system, everybody else should be on 12%, as explained by Will Crocket, film and digital professional photographer, founder of "shootsmarter.com"