Originally posted by bxf Apart from the above, something suddenly occurred to me: the entire concept of Total Light (to me, at least) is based on the question of why more light on a larger sensor is better than less light on a smaller sensor. Someone has presented an analogy of more water on a larger field improving the crop quality of the entire field, as compared to a proportionally smaller quantity of water on a smaller field.
So now I'm thinking: are we correct in assuming that light acts like e.g. water? In other words, is it possible that this is not a proportional thing? We know that twice as much water, on twice as much land, results in the same quantity of water per unit area. Do we in fact know that the same applies with light?
Yes, that analogy holds water
People often use it.
You can think of a photon of light as a raindrop, four buckets on one square meter on a 50 square meter field and on a 100 square meter field - those four buckets catch the same amount of raindrops.
But the 100 square-meter field catches many more total raindrops.
In
this link, the first graph ("screen") is the 4-buckets in one square meter comparison - looks the same. The second graph ("print") shows you the rain collected from the whole field.
Most people can get that. When a lot of people 'lose' that analogy is when they try to imagine how it applies to the
image, because the image isn't bigger/wider than the smaller-format image, it's the same FOV. The link you have to make in your mind is that the same-FOV image is being projected onto that sensor with a larger physical aperture, and then when displayed, it's constructed with more light as the main ingredient. Think of being delivered two 50 gallon buckets, one containing all water collected from the 50-sq meter field, the other containing all water collected from the 100 sq meter field. Both are 50 gallon buckets (same FOV,) one is just more full. Those 50-gallon buckets are your resulting images.
A simple different example that a lot of people seem to 'get' - but 'lose' when it comes to their cameras - you know how space telescopes like the hubble have huge mirrors, and huge physical apertures? An Iris you could lay down in, longer than your body? It's to
collect more total light. The more total light it collects, the deeper and more clearly it can see into space. (longer exposure time also collects more total light.) I think the primary mirror uses an iris 2.4 meters (not MM!), in diameter. That's a lot of total light.