Originally posted by redrockcoulee My silly spot meters have no place to input format size.
I already mentioned earlier that light meters do not need to distinguish between formats because they measure exposure.
Exposure is a relative measure of light-per-unit-area and hence independent of format size. Hence exposure, on its own, is unfit for predicting image noise. An image taken with a Q at f/1.9 will be much noisier than an FF image taken at f/1.9 (when viewed at the same size).
This is why the notion of "total light" is much more useful than "exposure". Only based on the latter one can suggest "f/2.8 = f/2.8“.
N.B., obviously physical lens properties never change, but the meaning of parameter numbers change between formats. Almost everyone understands that focal length requires a "currency conversion" between formats to allow focal length numbers to be compared, but not too many understand that the same is required for f-ratio and ISO.
I had already given up on this thread, and only replied because the post I quoted was an attempt to ridicule my position. I will try to abstain from replying in the future, but please note that
- I thought the thread was on course to steer away from an equivalence discussion, but several equivalence doubters kept on going back to that topic. I don't mind, but be careful about whom to blame when threads go off-topic.
- I thank Kunzite for his measured response. I still disagree with a number of his views, but he did not use aggressive language anymore. I did not respond to the post because I don't think that resolving our communication differences is of public interest.
- Bringing in t-stops complicates matters rather than simplifying them.
- "Equivalence in simple terms means trying to get the exact same image with two different formats.“ is a complete misrepresentation. The notion of "equivalence" is about a correct understanding of the impact of format size on image quality (noise and detail). While such a correct understanding allows one to figure out when images will be equivalent even when produced on different formats, it is inappropriate to equate a notion with one of its applications or, worse, claim that this application is the goal of having the notion.
- Noise is not driven by pixel size. The evidence exists on DxOMark. Here is a horse that won't stop dying, no matter how much one beats it. Yes, there are some highly technical second-order influences of pixel size on pixel noise, but the first-order effects and light shot-noise dominate and we are talking about image noise not pixel noise, hence one can forget about pixel size.