Calibrating digital exposure index

I wanted to establish the true ISO sensitivity of my Nikon D800e’s light meter in order to be able to use the digital version of the Zone System to visualise tonality and control placement of tones in the final print.

To do this I set my camera on to a tripod and aimed it at a grey card.

I set the camera to manual and focus to manual and set the camera at a distance that the grey card filled the screen and focused on to the card to infinity. I then set the ISO to the manufactures factory default setting for my camera, in this case ISO 100. This info should be mentioned in your manual or by simply resetting the camera to it’s original default settings from the menu controls.

Having set my camera to the default ISO, I mounted the camera to a tripod, set up a grey card in front of it filling the frame and focused to infinity. I then set an aperture that I can leave untouched. I set my camera’s light meter to matrix and set the aperture wide enough to provide a range of shots above a minimum shutter speed of half a second. The camera must be set to take images in RAW in order to be able to convert them to 16bit Tiff files without any alterations.

I then took seven sets of three images, each image 1/3 of a stops apart from the originally recommended shutter speed. The first set of three images was using ISO 100 as per my default setting with my first image with the internal camera’s light meter centred for a correct exposure for a Zone V mid-grey shot. I then took two more shots at ISO 100, one shot 1/3 stop above and 1/3 shot below the first shot.

Keeping to the same aperture and three shutter speeds the next six sets of three shoots was using ISO 50 (L1.0), ISO 64 (L.0.7) ISO 80 (L0.3), ISO125, ISO160, ISO200.

I then converted the RAW images to TIFF 16bit and without any imaging adjustments I simply compared the Histogram reading for each image looking for an image that closely matches the 128 value at the centre of the Histogram. The image set at an ISO that provides the closest 128 value on a Histogram represents the true ISO sensitivity for my camera.

From this exercise I established that ISO125 helps me place a mid-tone more accurately than using the factory default setting.

This exercise was taken from the book: Basics Photography 07, Exposure, David Prakel, AVA Publishing.

Leap of faith

I have started to take more control of my camera by manually setting the white balance to either the pre-set settings for sun, cloud, etc. or using a grey card and calibrating the camera under the current ambient light conditions at the time.  In the past I opted to trust the camera to decide for me; but I am taking lots of photos of the same subjects for this course all with the same light conditions etc.   I want to be able to take advantage of the batch processing featured in Lightroom or NX2 in order to quickly and efficiently make adjustments to my RAW files and in order to do so I must me sure that the batch of images all have the same WB for the process to be effective on all the shots.  It is easy to be lazy and let the camera do the thinking; so it takes a little leap of faith to start owning more of the responsibility of setting the camera up for good and correct exposures.