What to buy for shooting action that doesn't cost as much as a D4?

Started Nov 14, 2013 | Discussions thread
OP jfriend00 Forum Pro • Posts: 12,367
Re: I don't know about EV's but ...

Grevture wrote:

jfriend00 wrote:

Grevture wrote:

lock wrote:

But of course you can go lower. However, how often does it happen when shooting sports ?

Well, have never bothered with EV, so I have no idea where that puts you

But to me, decent low light is at say iso 3200, f2.8 and 1/500, while quite bad light is at iso 6400, f2.8 and 1/250. Following that I find the 51 point system somewhat better in decent light, and in quite bad light the 39 point AF just is nowhere near the performance of the 51 point version.

I think the point of the recent discussion here is that how an AF system works in low light has more to do with the focus processing behind the scenes (e.g. in the circuitry) and less to do with how many actual AF points there are. There might be a loose correlation between number of focus points and focus horsepower (just because Nikon chooses to align more horsepower with more points), but they are different parts of the system so we know they are not always correlated. For example, the D300 and D3 had the same 51pt AF part in it, but the D3 was way more powerful for AF in bad light.

Similarly, we really don't know how the Df, D610 and D7000 compare in focus horsepower even though they all have 39 focus points. And, I've seen evidence that the D300 does noticeably better in low light than the D7100 even though they both have 51 points (in fact, the D7100 part is newer as it works at f/8 whereas the D300 does not).

So, I've concluded that you can't just assume a level of performance because of the number of focus points. There's so much more to it than that.

I am not particularly interested in the number of points as such - what I am saying is the 39 point system (as a system) is less well adopted to low light then its 51 point counterpart. I think the difference probably is about smaller individual AF points (thus gathering less light) in the 39 point variety - that version appear to have been designed for cheaper camera models then the 51 point version.

And I would be very interested to see the evidence supporting the D300 AF doing noticeably better low light then the D7100 AF - from what I have seen, its is the other way around (which would make sense since the 51 point system got better in low light also in the D4 and D800 as compared to D3/D3s and D700).

The part I do agree with is the total performance of a AF system is a combination of the AF sensor (being a 9 point, 11 point, 39 point or 51 point version) and the processing horsepower behind it. I have seen many reports the D300 gaining slightly in overall AF performance with the battery grip (along with gaining fps speed), which could be because the camera is allowed to use more power for processing with the battery grip then without.

We're mostly in agreement here.

What I'm trying to say is that it's not safe to generalize based on the number of AF points.  For example, do you think the Df, the D610 and the D5300 all have the same AF performance just because they all have a 39pt system?   Or do the D7100, D800 and D4 all perform the same because they all have 51pt systems?  Or can we know that the D7100 performs better than the Df just because it has more points?

I think what matters even more than which AF sensor unit the camera has is the processing unit behind it (it probably comes down to focus calculations per second and subject tracking logic and noise suppression and stuff like that in the electronics behind the focus sensor).  I refer to this processing stuff as "focus processing horsepower" because I don't know of any other name for it and Nikon does not discuss any of this.  But, we know that the D300 and D3 both have the same focus sensor, but the D3 is clearly more capable at focusing and tracking - especially in low light, at max fps or with low contrast subjects.  I theorize that is because it has more "focus processing horsepower".  You could see this in the 3D processing too.  The D3/D3s were sometimes passable in 3D mode, the D300 was basically never useful in 3D mode.

There may be a general correlation between number of focus points and the amount of focus processing horsepower and overall system performance such that 51pt based systems may have more focus processing horsepower than 39pt systems and thus perform better just because Nikon chooses to align the more expensive part with the better focus processing horsepower. But, I don't think you can conclude that all 39pt systems have equivalent performance or all 51pt systems have equivalent performance.

If I can find the source of the info about the D300 AF performing better in low light than the D7100, I'll post it - don't have it handy now.

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