Have now tried 3 times to do this, first two times, the info at 1/60s was way out - then realised that I was shooting raw files and the raw editor was adjusting - aaggghhhhhh - note self - put brain in gear.

The third set taken as jpegs came a lot closer to the expected results except the true black which I assume will be the image taken at 1/1000s, I am getting readings that show some detail is apparent that is 7 7 7 top right hand corner, 8 8 8 in the middle and 6 6 4 bottom left.

Am I right in assuming that these should be 0 0 0 across the image - i.e true black. If so I must be getting some trace light onto the card that I was not aware of.