Originally posted by Steelski How am I wrong, only 70% of the light gets through, if it was 50% it would be half the light. AKA 1 stop. 70% of light getting through is a loss of 3/5ths of a stop, which is larger than 1/2. It is 60% of a stop light fall off.

I am not wrong. Its just a different way of stating it.

I could state that its more than a 50% of a stop light fall off. which would also be right. Roughly 1/2 a stop is also right, although less accurate.

How could you be wrong? Because your reasoning assumes a linear relationship between % of light loss and the same in stops/Ev. The relation is not linear, its exponential.

30% loss is exactly 0,514573 Ev. 1/2Ev would be 0,5 and 3/5Ev would be 0,6. You tell me which is closer to 0,514573, 0,5 or 0,6, and as such more accurate...

It's not a major issue however. And in practice it's the images that matter.

Wim