sarangiman said:
neuroanatomist said:
[quote author=DP Review]
The D750 inherits a version of the 51-point Multi-CAM 3500FX AF system that we've seen used in the D800/E and D810 but its 'II' version is actually more sensitive rated down to -3EV. We haven't been able to really get a feel for how much difference this makes in normal use but in theory, the D750 should offer superior AF reliability in poor light compared to the D810 and D4S, which is quite something (and which might prompt more than a few D800 owners to 'upgrade' to the D750).
As I've stated before, people make too much of this spec. Consider an example of the difference between -2 EV and -3 EV light levels: f/2.8, 1/15 s, ISO 51200 vs ISO 102400. Neither of those is likely to result in a very good image in most situations.
Whatever (likely hardware?) change that enables focus to work down to -3 EV might, just might, make the system also work better and more reliably at, say 1 or 2 EV. That would be advantageous.
I'm not saying that's the case, I'm just saying it's likely and that if it *is* true then that would be pretty worthwhile.
What'd be nice would be if someone tested this thoroughly. But before that, I think it's premature for anyone to make the comment you did - completely ignoring the potential benefits at slightly higher, yet still low, light levels. We all know very well that precision of AF points drops with lower light levels and lower contrast; anything that increases the SNR of what the AF sensor 'sees' could help performance in situations other than just -3EV.
Let us know if you think that's completely false.
All that said, I do wish Nikon put some more revolutionary changes into the AF system. Canon's been, admirably, iterating quite a bit on their AF sensors, if I understand correctly.
[/quote]
Interesting that this went unanswered. Neuro: if you don't have any solid evidence that the -3 EV rating *doesn't* help in other, less drastically low-light settings, then please don't go around spreading misinformation that its of no utility to shooting scenarios other than those extreme ISOs (51k and above) you mentioned.
I'm saying I don't know, as I haven't had a chance to test it yet, but common sense dictates that if the AF sensor can focus in lower light, then it's probably going to better in other, more reasonable, low light scenarios as well (like EV 2 or 3 or what have you).
This was certainly the case for the A7S, for example. Just b/c it was rated down to EV -4 didn't mean that's the only place it was useful. It'd focus far more quickly and reliably than the A7R in less low-light scenarios as well. And this isn't surprising - if you're not pixel-binning, then each pixel used for focus has significantly lower SNR. Thus, AF is more likely prone to failing in low light, especially with low contrast subjects. And if you're only pixel binning at the software level, you've got all the extra read noise of the extra A7R pixels (which, importantly, don't individually have lower read noise than the A7S' pixels).
Of course, the fact that the A7S' EV -4 rated AF is still only CDAF usually meant that a 5D Mark III, for example, would still outperform it when shooting actual moving subjects in low light (b/c PDAF only needs to make a few measurements to nail focus, whereas CDAF needs to continuously hunt - during which time your subject may move significantly, throwing CDAF completely off.). That said, Sony was correct in saying the A7S would focus in lower light levels than any competitor DSLR - but I found that was only true for static subjects. The sampling intervals get longer in lower light (so AF slows down) and if your subject is moving - good luck to any CDAF system. The subject usually ends up moving before CDAF is able to make enough measurements to complete focus.
