Quote Originally Posted by Stephen Benskin View Post
The testing under the ISO standard and the determination of the ISO triangle is done under no flare conditions. Rafal's test consisted of sticking the step tablet up against the window and shooting it with his camera (optical system). He emphasized the need for testing under daylight conditions but missed that such a set-up will produce flare. As we know flare compresses the shadow area. ISO speed is determined using the gradient of the shadow. CI is determined more from a fuller range of the film. In order to raise the gradient of the compressed shadows sufficient enough to fit into the ISO triangle, the CI will be excessive like we see with Rafal's examples.

What is happening here is that a non-flare interpretation is being used with a test that incorporated flare. Any results are questionable at best.
Thanks for pointing this out. On this thread I asked about the correct way to photograph the transmission tablet. It was suggested that I should tape it to a window. In post 7 I was concerned about any reflections from the surface of it, when it is taped to a window.

Are those reflections the main source of the flare that you are referring to, or could they be an additional reason for the steep curves which resulted in my test?