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Limiting factors on AF tracking speed

caf focus tracking focusing speed

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8 replies to this topic

#1
Dogbytes

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A question for the technical amongst you and the sports/action shooters...
I take a lot of pics of dogs, very fast dogs and they’re often shot running towards me. They move at a bit over 40 miles per hour and being quite small (compared to a car, for example) I usually use as long a lens as possible and let them get as close as I can.

This introduces a number of requirements - I need a high shutter speed (obviously!) and experience has shown that 1/1500 is enough though 1/2000 is ideal. Living in the U.K. where sunshine is not necessarily guaranteed(!) means using as wide an aperture as possible both to achieve the high shutter speeds without losing too much quality to high ISO settings and to isolate the subject.

I find I lose a lot of otherwise decent shots to focus errors. That is particularly apparent as the dogs get closer and I’ve come to the conclusion that the camera/lens struggles to track focus under these conditions. At longer distances where the range difference is not so great and depth of field is greater, I dint have the issue.

I remember with the old ‘D’ screw-drive lenses, the film-era pro bodies - particularly the F5 were known for their extremely powerful focus motors which were able to focus the lenses noticeably quicker than the consumer camera bodies.

My question is this...
Using modern ‘S’ and ‘P’ lenses, are modern pro bodies able to focus quicker than consumer bodies - due to faster data processing, for example?
Do some of the lenses focus faster than others due to more powerful motors?
If so, which ones?

I currently use a D610 and, for dog racing/action pics a Nikkor AF-P 70-300 f4.5-5.6 E VR. Which of the two is likely to be the limiting factor in terms of tracking focus with the subject moving towards the camera?

I’m hoping to get a D850 this year, will that focus quicker with the same lens or would I be better keeping the D610 and getting the latest model 70-200/2.8 lens?

Looking forward to hearing your views...

#2
Merco_61

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The pro bodies drive the lenses faster as they get the full voltage they were designed for if you use an EN-EL18 battery.

The faster and more refined AF processing will make a difference, even if you use the standard batteries.

I don't remember how many of the focus points in the D610 are cross-type, I think the outer points are horizontal detection only. If that is the case, you will see a marked improvement. Most, if not all, of the focus points in the D850 are capable of reliable AF @f/8. This gives a bit of margin in low light compared to the f/5.6 limit of the D610.



#3
mikew

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Have you made this comparison as to focus point sensativity, i know your talking full frame but i chucked the D500 in.

 

Nikon DSLR | Cameras for Photography and Video



#4
Dogbytes

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Have you made this comparison as to focus point sensativity, i know your talking full frame but i chucked the D500 in.

Nikon DSLR | Cameras for Photography and Video

I hadn’t done that. That’s quite a useful and informative tool
I’d still be interested to hear the views of actual users rather than Nikon’s marketing team - who, I’m sure are scrupulously honest and not at all biased... :D

The pro bodies drive the lenses faster as they get the full voltage they were designed for if you use an EN-EL18 battery.
The faster and more refined AF processing will make a difference, even if you use the standard batteries.
I don't remember how many of the focus points in the D610 are cross-type, I think the outer points are horizontal detection only. If that is the case, you will see a marked improvement. Most, if not all, of the focus points in the D850 are capable of reliable AF @f/8. This gives a bit of margin in low light compared to the f/5.6 limit of the D610.


Hi Peter, I was hoping you’d reply.

The EN-EL18 is the battery used in the battery grip, yes? I knew that that would enable the full-speed continuous drive (9fps instead of 7fps) but I hadn’t realised it was a matter of battery voltage and could affect the speed of the focussing motor in the lenses. That is interesting. What if I add a battery grip to the D610?

From memory the D610 has only 9 Cross type focus-points. It would also appear that the D850 (along with the D5 and D500) have about a four stop advantage in metering range over the D610.

I find myself wondering how the forthcoming (I think) D760 will fare in this regard.

Cheers
John

#5
Merco_61

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The grip on the D610 only adds capacity as the extra battery is the same type as in the body. These are 7V batteries, the EN-EL18 is 10.8V.



#6
Dogbytes

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So, a bit of research seems to indicate that the D850 would offer a significant improvement, even with the zoom that I’m using, with the possibility of even quicker performance if I added a battery grip and the EN-EL@8a battery.

Just got to raise the cash now, which brings to another point...

Here in the U.K. a new D850 has a recommended retail price of £3114 inc VAT. which is a bit cheaper than they used to be. They can of course be had for a little less than that but grey imports can be had for only slightly over £2000 - a significant saving. Some of these sellers claim to offer 1 year warranty, UK plug for the charger, etc. Downsides?

#7
Merco_61

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The warranty is dependent on the seller surviving.

Warranty work (or really any repairs) can take much longer than with an UK market camera as they will probably have to be sent to the country the camera was meant for.

You will have to decide if the risk is worth the savings, or not.



#8
Jerry_

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I hadn’t done that. That’s quite a useful and informative tool
I’d still be interested to hear the views of actual users rather than Nikon’s marketing team - who, I’m sure are scrupulously honest and not at all biased... :D

I fully share Mike’s view on considering the D500 for the type of use that you describe.

I have both the D610 and the D500 - and while I am looking into replacing the D610 with a D850 for landscapes the D500 will stay my favourite when it comes to fast moving subjects.

You may have noticed that while the D500 has a DX sensor it has the FX sized focus sensor field of the D5. As a result focus points are spread much wider over the capture. Obviously the one closer to the border are less accurate, but the ones in the center of the image allow to have the focus really down to the spot.

Also, due to the cropfactor, you may choose a lens with a shorter focal length to get the same angle of view.

My recommendation for your type of photography would therefor be a D500 while having a fast lens for the difference in price to the D850.

#9
Dogbytes

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I fully share Mike’s view on considering the D500 for the type of use that you describe.

I have both the D610 and the D500 - and while I am looking into replacing the D610 with a D850 for landscapes the D500 will stay my favourite when it comes to fast moving subjects.

You may have noticed that while the D500 has a DX sensor it has the FX sized focus sensor field of the D5. As a result focus points are spread much wider over the capture. Obviously the one closer to the border are less accurate, but the ones in the center of the image allow to have the focus really down to the spot.

Also, due to the cropfactor, you may choose a lens with a shorter focal length to get the same angle of view.

My recommendation for your type of photography would therefor be a D500 while having a fast lens for the difference in price to the D850.


Believe me, I have considered this option and, if I ONLY did that kind of photography, I would probably go that route but I use my camera (and I prefer to have just the one, for several reasons, not least financial considerations) for all kinds of photography.

I like full frame for limiting depth of field, and although I don’t particularly need more than 24mp, now that I’m used to it I wouldnt want less. Id be interested to see how the probably forthcoming D760 is equipped as regards focusing/metering/resolution.

The D850 has a side effect(!) of having that 46mp resolution. That could enable me (down the road a bit when finances have recovered!) to use a 70-200mm/f2.8 instead of my 70-300 and have enough pixels to crop - particularly given the 2-stop, hence lower ISO/higher shutter speed advantage of the 70-200.





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