I seem to be in the minority of people who still get excited by increasing maximum ISO speeds. But can someone explain, why/how is it possible that the difference between maximum base ISO (25600) and extended is 4 stops, whereas in Canon cameras (the 1DX/5D3 at least) it is just 2? Does it make a practical difference? Is it just another means of notating it? In my experience (300D->50D->5D3) the highest usable ISO is 1 stop below maximum base ISO (depending on what you're using it for). So extra extended settings would be irrelevant. Is Nikon different?The range of uses ISO standard real analog signal amplifiers in each stage (100, 200, 400, etc.). The expanded ISO range is the same as Photoshop / Lightroom just pulls exposure digitally generating artifacts and random noise difficult to clean.
I've heard conflicting reports on this - some people say digital amplification is sometimes used within the non-extended range. But if you're correct, there's no advantage to having 4 extended stops over 2, right?
Current equipment: 5Ds, 5D mark III, 50D, 24-105L, MP-E, 70-200 f/2.8L II, 100L macro, 500L IS II; 1.4xIII + 2x III extenders; 600EX-RT.
Former equipment includes: 300D; EOS-M, EF-M 18-55, Samyang 14mm f/2.8, EF 35 f/2 IS, 70-200L f/4 non-IS, 85L II, Sigma 180 macro, 200L 2.8, 400L 5.6