« on: February 26, 2014, 01:28:02 AM »
I suspect what Marsu42 is referring to is the decrease apparent aperture, the light loss you get as magnification increases.
Indeed, but it's not "apparent" but for real, unlike Nikon Canon just chose to hide the fact that a f2.8 lens @1:1 doesn't get f2.8 light through anymore... that's why the shutter speed gets longer like by black magic. I just read up about it again, it's called "effective f-stop": http://www.cambridgeincolour.com/tutorials/macro-lenses.htm
There's no 'magic number' for that, there's no 'macro mechanism'
Imho there is, it's the "extension" that only a real macro lens has.
At 0.2x mag you lose ~0.67-stops of light, at 0.5x mag you lose ~1.33-stops, and at 1x you lose ~2-stops.
Ah, thanks, that were exactly the numbers I was looking for. Now I'd only need to calculate how much effective f-stop difference there is for crop vs. ff for some scenes, but what you wrote indicates ff still has a slight advantage, though to a much smaller degree than at non-macro distances. But *plus* you still need a smaller aperture to get a usable dof, so that means even higher iso on ff for the same framing.
That, the dr loss at the higher iso for ff, the working distance & swivel screen still make me use the 60d :-)