The following thee images of black card, white card and mid grey card were taken with my camera set on automatic. No other details were present within the frame. The result is that as the camera while on automatic assumes that whatever you fill the frame with will equate to the average then as there are no other colour present the picture will always look like a mid grey. The histograms reflect this by having a central tendency. There seems a slight consistent bias to the right but that was probably due to shooting factors.
With these pictures I adjusted the exposure so as to move the histogram from the middle to the left and the right without regard of speed and aperture. While the pictures visibly look acceptable in difference of tones versus the original card something does not look right with the exposure figures. I would have expected the range to be only plus or minus 3 or 4 stops. However looking at the difference between the back and the mid-tone I think I must have made the speed to fast. Regardless of how much of perfect or underexposure the picture will always look black
Here I have taken a picture of the mid grey card and exposed it ‘correctly’ on fully manual. The next two pictures I replaced the grey card with the white took a shot, replaced with the black took a shot while not changing the exposure. The theory is that if the grey is truly mid-grey then this should be the average, therefore the black should therefore the black should be true black and the white true white. Looking at the histograms and the pictures this is almost true allowing for the fact that the grey is probably not exactly mid grey and there were slight variations in the taking. Note is the histogram data the exposure data remains constant.
A couple of post exercise thoughts:
- Would the results be any different if I used spot metering instead of average metering? I think the answer would be no as the results would be the same because there was no other detail showing on the card. If there were some other objects showing then spot metering would have been more ‘accurate’.
- Would the result be any different if I used an external light meter? The answer is yes because the external meter is measuring the incident light it disregards how much light is reflected. Therefore the tonal rendition of the black, white and mid grey should be exact. (I will see if I can hunt down an external meter to test the theory and add at a later stage).