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Nikon DSLR Body Auto-focus Motor Quality

Mark Fukui , Nov 04, 2010; 04:59 p.m.

Hi guys,

I realize that models, with the D50 as the exception, above the D90 have an auto-focus motor built into the camera body, and models below do not. I was wondering if the auto-focus motor differed in quality lets say from the D50 to the D90 to the D3? It would makes sense that there is some small difference that would favor the D3, but is it a large difference? I am just wondering because i would like to know that if the motor in the D50 would negatively effect auto-focus speed for a demanding environment such as sports? As far as i am concerned the auto-focus speed, which is determined by the built in motor depending on what lens one is using is going to be a tad faster as you go up the chain. For example D50

Thanks!

Responses


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Matt Laur , Nov 04, 2010; 05:20 p.m.

I'm thinking that the difference between the D300's (for example) AF brains (and sensors, of which there are many more) and that of the D50's will make far more of a difference in AF responsiveness and accuracy than will the difference between their mechanical AF systems.

Hector Javkin , Nov 04, 2010; 05:43 p.m.

Nikon does put smaller and less powerful motors in its less expensive bodies, when it puts them in at all. I agree with Matt that differences in processing power play an important role in AF speed differences.

However, the effect of the different motor sizes vary with lenses. A relatively heavy lens like the Nikon 80-200mm f/2.8 (non-S, without its own motor) is very slow on a D50, not so bad on, say, a D300. Its heavy elements and mechanical components make big demands on the motor. There is not so much difference in the AF speed between these bodies when a 50mm f/1.4 is mounted.

With small, light lenses, then, processing power makes the biggest difference. With heavy lenses, the in-camera motor makes the biggest difference. That is why Nikon's going to motorized lenses, and (sigh) Canon's having them all along (for its present lens mount) makes sense. The motor can be sized according to the demands that will be put on it.

Eric Arnold , Nov 04, 2010; 06:45 p.m.

the pro models have stronger focus motors and better AF modules, along with 4-channel output for fast focus lock and near instantaneous capture. they are built for speed and also built for sports.

your question, whether a d50 would negatively affect AF speed for sports, is phrased somewhat awkwardly. by that i mean, if you are asking, would a d200, d300, d2x, d3, d3s, or D3x be faster in general, the answer is yes. and, if you are asking, would a d50 focus faster with an AF-S or HSM lens over a screwdrive or micromotor lens, assuming we're comparing apples to apples, the answer is also yes.

one indication of processor speed is the frames per second rate. the d50 is one of nikon's slower bodies, at 2.5fps. so it's no speed demon.

but like hector says, lenses are the other half of the equation. a 50/1.8 has a very short focus throw. it will AF faster than some consumer-type AF-S lenses, even on a d50, because it doesnt have very far to travel to acquire, lock and maintain focus across the focal path.

interestingly, some screw-drive lenses are faster than micromotors, even on a low-end body. and short primes will focus faster than some AF-S zooms. with a d50, you can use non AF-S lenses and still AF, so that's something to keep in mind if you are shooting sports.

similarly, an 18-200 will focus more slowly than an 18-70 or 18-55, especially if you are going from one end of the zoom range to the other. they all have consumer-type AF-S, but the focus throw of the 18-200 is much longer. a nikon pro lens like the 70-200 or 24-70, will have a faster AF-S motor than a kit lens. i think sigma also puts better HSM motors in its upper-echelon lenses than some of its lower-end glass.

Allan Armstrong , Nov 04, 2010; 06:57 p.m.

My 300 f4 AF screwdrive lens is pretty good on my D90, but my 70-200 f2.8 VR2 smokes it. I swapped lenses once with a guy at the races who had a D3 and a 70-200 f2.8 VR1. He thought the 300 f4 was pretty fast. It may be faster on the D3.
Given how fast the 70-200 VR2 is, I probably will use the 300 f4 screwdrive only on very rare occasion now.
Eric -- what does "4-channel output" mean?

Professor K. , Nov 04, 2010; 07:29 p.m.

The more money you spend at any point in time, the better the autofocus algorithm and the more powerful the motor. In the past I have used the old 'screwdriver' 300mm Nikon on a D70 and also on a D2H. Absolutely no comparison! Not even close. Not only was the D2H far better at acquiring and staying on birds in flight, but the brute force of the motor was truly impressive.

Emilio Gutierrez , Nov 04, 2010; 07:48 p.m.

There are plenty of differences among the AF motors on Nikon bodies. I found the one on the D80/D90 series slow and underpowered, the D300 has a much better one. The D2 and the D3 both have a nice, fine-tuned motor you can tell it was engineered with precision in mind, very good torque to.

To me the most awful of them all is the one on the N90 series, slow and so noisy I rather focus manually when using that camera. The one on the F5 though still has the most torque in my perception.

Eric Arnold , Nov 04, 2010; 08:24 p.m.

Eric -- what does "4-channel output" mean?

it basically means double the processing speed as 2-channel output*. this is something nikon put in the d200, d300, d2, and d3series, which you won't find in d90,80,70,60,50,40, etc. it doesnt really come into play unless you are shooting fast action at high frame rates. but it's a reason why the pro nikons are faster than entry-level models.

*i'm sure there's a highly-technical explanation available on nikon's website, but i'm too lazy to look it up.

Mark Fukui , Nov 04, 2010; 09:12 p.m.

Thanks for the input. I was considering buying the nikon 80-200mm f2.8 along with a used D50; but, i am starting to shy away from the idea especially since i wanted to use it for sports. I really want to shoot sports; I can't find a very cost effective way to do it. I might settle for the sigma 24-70mm f2.8 hsm, but now i am getting off topic. The explanations really help. I couldn't find a high quality response like this from google. :D

Leigh B. , Nov 04, 2010; 11:41 p.m.

Is it April 1st????

With the exception of the old F3AF system, all Nikon lenses have internal motors that control focus.

There's no focus motor in the camera body.

- Leigh


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