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Forums Lobby GET TO KNOW YOUR CAMERA & MASTER IT Nikon D90/D80/D70 (Public) topic #218144
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Subject: "Auto focus Spec." Previous topic | Next topic
stev32k Registered since 27th Dec 2003Sun 22-Feb-04 12:40 PM
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"Auto focus Spec."


Mobile, US
          

There has been quite a bit of discussion in other forums about the Canon D10 and D300 auto focus problems. Seems the AF specification for the D10 is 1/3 the depth of field, and the D300 is 1 DOF. Does anyone know the Nikon AF specification?

  

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Len Shepherd Gold Member Nikonian since 09th Mar 2003Sun 22-Feb-04 03:29 PM
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#1. "RE: Auto focus Spec."
In response to Reply # 0


Yorkshire, GB
          

>There has been quite a bit of discussion in other forums
>about the Canon D10 and D300 auto focus problems. Seems the
>AF specification for the D10 is 1/3 the depth of field, and
>the D300 is 1 DOF. Does anyone know the Nikon AF
>specification?

This is an interesting question I cannot answer other than to say if the Canon figures mentioned are accurate the D300 is next to useless as all dof can be in front of or behind the focus point meaning that the AF can be way off target.

Taking an extreme example of what good AF needs to do the Nikon 500 f4 AFS has 3 inches total dof at 25 feet focus distance at f4 so total dof is less than 1% of focus distance.
As the AF system has to get the focus distance "in the middle" it has to focus to an accuracy of 0.5% or better (less than 1 inch).

At 50 feet f11 total dof is 7.5 feet (90 inches)and ideally the AF should focus 3.5 in (the point of critical focus) so three inches either way (0.5% of focus distance)would go unnoticed.

The amount of dof field increases more rapidly than focus distance as you focus further away so AF has to be very good to be accurate in close up, especially wide open.

What I can say is that for any multi focus point AF system selecting only the central focus point is always the quickest and most accurate.

Some sensors focus better than others in most system and AF speed and accuracy tends to be lower with smaller maximum apertures.

***

As regards focus tracking speed Nikon say in the F5 brochure the F5 and 300 f2.8 AFS works with a subject traveling at 300 kilometers per hour (about 120 mph)as close as 19.3 meters (about 65 feet).

***

Do not overlook lens drive accuracy.
The 28-105 screwdriver drive goes from infinity to half life size in under 3 revolutions.
The 80-400 only goes to one fifth life size and takes 22 revolutions.
Guess which lens has the most accurate AF regardless of body used!



Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.

Len Shepherd

  

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stev32k Registered since 27th Dec 2003Sun 22-Feb-04 03:55 PM
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#2. "RE: Auto focus Spec."
In response to Reply # 1


Mobile, US
          

<This is an interesting question I cannot answer other than to say if the Canon figures mentioned are accurate the D300 is next to useless as all dof can be in front of or behind the focus point meaning that the AF can be way off target.>

Yeah, there are a lot of people upset about this. I've seen several examples where the focus point was behind or in front of the subject. What's worse is that the focus error is random - one time it's behind and one time it's in front. Canon will not fix the problem because it's within the operating specification. There are several D300s listed on ebay for this reason.

  

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stev32k Registered since 27th Dec 2003Sun 22-Feb-04 10:01 PM
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#3. "RE: Auto focus Spec."
In response to Reply # 1


Mobile, US
          

<Do not overlook lens drive accuracy.
The 28-105 screwdriver drive goes from infinity to half life size in under 3 revolutions.
The 80-400 only goes to one fifth life size and takes 22 revolutions.
Guess which lens has the most accurate AF regardless of body used!>

I don't really know the answer, but I would guess that the 80 - 400 would have the most accurate focus. Right?

  

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