I post too Much on Here!!
- Jul 21, 2010
Oh, so you’re going to be literal. That’s fine. The EF 100-400 f/5.6 is brighter than the RF 100-400 f/8 because the former is painted white and the latter is painted black. Brightness is emission or reflection of light, and the maximum aperture of the iris diaphragm inside the lens changes neither. Paint color affects brightness. I suppose you could also put a light bulb inside a lens to make it ‘brighter’. Likewise, an f/8 lens can be faster than an f/5.6 lens if the former is being transported by jet plane and the latter is being carried by someone walking on a trail.Let's review. JohnOnTheNet said:
I replied that this was not correct because:
Neither one of us said anything about DOF, noise, or "equivalence". The statements were only about the lens being "brighter", i.e, providing greater luminous flux density, when used with one sensor versus another. But the properties of the lens do not change because there is a different size sensor behind it. the amount of light per unit area reaching the sensor is the same (assuming the lens can illuminate the full sensor).
In the context of the original statement, my response was correct and I feel no need to defend it further. Personal attacks on me, @neuroanatomist, won't change that.
Now that we have silliness out of the way, it’s pretty obvious that the original comment was in reference to equivalence, since it’s unlikely that someone would be silly enough to suggest that f/8 transmits more light than f/5.6. (Note that I mean relatively more light, since the f/number is a ratio it’s quite possible for an f/8 lens to transmit more absolute light through the iris diaphragm than an f/5.6 lens, if the latter has a sufficiently shorter focal length.)
You just decided to take an unrealistically narrow and silly approach to interpreting the original statement. I did so intentionally above, and I trust you see how ridiculous that approach comes off.
Still, I apologize for my harsh response. But honestly, claiming that total light gathered is meaningless for photography is about as asinine as saying a lens is fast because it’s being transported in a jet.