Does the body determine the focus speed of a lens?

[mark_stephan2]

<p>Out of curiosity I was comparing my 100-400 (first version) between my 70D and my ancient 1Ds and the older body seemed faster in the same lighting, same subject situation. Is it true that high end bodies focus faster than mid range bodies or has the 70D/80D caught up is situations where you need fast AF? IMO the 70D was almost as fast and is the better body for my attempts at wildlife photography.</p>

[dcstep]

<p>The 1Ds is several generations old. Put a teleconverter on you 100-400mm and then try to AF with your 70D and the delays will be unbearable. Put the same lens/TC combination on a 1D-X and it'll fly in comparison. With the larger lenses, like the 500/f4, the differences get even more noticeable. With the bare lens, there's not a whole lot of difference in acquisition speed, but add the TCs and it can take a full second to acquire focus, where a 1D-X will be almost instantaneous. </p>

[ed_avis2]

<p>I believe there is a difference with the bigger lenses like yours. The bigger camera body has more battery power to drive the focusing motor to move the heavy lens elements around.</p>

[JosvanEekelen]

<p>Chuck Westfall use to write on things like this on http://digitaljournalist.org/archives.html . The site is no longer maintained, perhaps you can find an answer in the archives. Older columns seem to be available. </p>

[steve_dunn2]

<p>The body and the lens both play a role in how quickly autofocus works.</p>

 

<p>The body's AF system has to determine what needs to be done to bring the subject into focus. As a general guideline, newer and higher-end bodies tend to do this more quickly than older and lower-end bodies do. Other factors such as lighting come into play, too, and may not affect each body equally (one body, for instance, might lose more of its AF speed in poor light than another body does).</p>

 

<p>Once the body gives the lens its command, then the speed is up to the lens, and again various factors come into play. The type of AF motor and the quantity of glass that needs to be moved obviously both play a role. The CPU in the lens (each lens has one) and the firmware it's running also can have an impact. And the lenses that are compatible with teleconverters intentionally slow down AF drive when a teleconverter is used, trading some performance for improved accuracy.</p>

[ed_avis2]

<p>Steve D., are you sure that's the whole story? The 1DX and the 5D3 have the same autofocus system, but the 1DX is said to focus big lenses faster since it can provide more power to the lens motor. That might be a marketing myth but it needs to be considered.</p>

[dcstep]

<p>Steve Dunn wrote a nice theoretical piece, but it's wrong.</p>

<p>Take it from someone that's shot Series II super-telephoto lenses with the 7D, 5D MkII, 7D MkII, 5D MkIII and 1DX, with and without the EF 1.4x TC-III and the 2.0x TC-III. The differences in the body can make a HUGE difference in AF acquisition time and tracking accuracy. The 1D X is the champ, by a long shot, when using the 2.0x TC-III and the it's the best with the 1.4x TC-III, but at a much smaller and more manageable difference. With bare lenses in decent light, there's very little difference between the 1D X, 5D3 and 7D2. They share AF firmware, mostly, but the 1D X has a higher voltage battery.</p>

<p>With either the 5D3 or the 7D2, combined with the EF 500mm f/4L IS II and the EF 2.0x TC-III, the acquisition time is around 1-second. With the 1D X and the same lens setup, the acquisition time is around 1/10-sec. When shooting BIF, that's huge.</p>

[ed_avis2]

<p>David S., that's interesting. The fact that the difference appears when using teleconverters (which do not change the amount of work the motors must do to move lens elements around) makes me wonder whether this is a software issue. The teleconverter tells the camera body to focus more slowly, which may be necessary in some cases because of the longer effective focal length and reduced effective aperture. The less expensive bodies slow down their autofocus accordingly, but the 1DX does not, or not as much. That is a convenient selling point for Canon, of course.</p>

[dcstep]

<p>I think there's also a difference with bare lenses, but it's hard to detect without test instruments. My friends moving from the 7D2 to the 1D X and using 500/f4 and 600/f4 report better AF consistency. In AI Servo mode, which most of us use for BIF, the AF system is constantly correcting. We're told that the software is the same, so battery voltage could be a factor....or, they could be lying to us about the software being the same. ;-)</p>

<p>The 7D2's battery is 7.2-VDC with 1865mAh and the 1D X MkII's battery is 11.1-VDC and 2750mAh. That doesn't give us the whole story about relative "cranking power", but I suspect that's a difference maker. Artie and Arash, over at BirdPhotographers.net say that Chuck Westfall told them that battery voltage is a primary factor in the 1D superior AF performance. It's likely not the only factor. They've also said that the Series II lenses and the Series III teleconverters have chips to improve their performance speed. So, to hit on cylinders in the AF arena, you need a complete system of the latest equipment.</p>

[glen_h]

<blockquote>

<p>The teleconverter tells the camera body to focus more slowly, which may be necessary in some cases because of the longer effective focal length and reduced effective aperture.</p>

</blockquote>

<p> <br>

I have a Tamron 2x for Nikon mount. For the older AF lenses, with the motor in the camera, there is a coupling through the TC with a 2:1 gear reduction on the AF. But with the motor in the lens, there is no reduction. When using that one with motor in the lens, it seems to overshoot, oscillate around the right focus, and usually not settle down to the right spot.</p>

<p>Do Canon mount lenses allow the camera (or TC) to change the speed?</p>

[dcstep]

<p><a href="/photodb/user?user_id=4549066">Glen H</a> <a href="/member-status-icons"><img title="Frequent poster" src="/v3graphics/member-status-icons/3rolls.gif" alt="" /></a>, asked:</p>

 

<blockquote>

<p>Do Canon mount lenses allow the camera (or TC) to change the speed?</p>

</blockquote>

<p>Canon brand lenses and TCs have internal chips and motors that are controlled by the Canon body that they're mounted to. Mix any another brand or an older series lens or TC and the behavior may change. Use Series II lenses with Series III TCs and bodies made after the 1D X was introduced, for best results.</p>

<p>I know for a fact that AF is impacted by both physical attributes, such as f-stop and software. When I first bought my Canon 5D MkIII, it would not AF at f/8. A few months after its release, a Firmware update was issued, which allowed for AF at f/8.</p>