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Fuji 50-140 f2.8 automatically refocus or parafocal featu...
  
 
millsart
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p.1 #1 · p.1 #1 · Fuji 50-140 f2.8 automatically refocus or parafocal feature ?


Just noticed something on my 50-140 f2.8. If I lock focus on a subject, and then turn the zoom ring, the lens will automatically adjust the focus. The lens optically is not parafocal, meaning that you can focus at one focal length and keep the subject in focus if you then turn the zoom ring, most lenses aren't these days. Never really noticed before that the lens and/or camera body seems to be trying to adjust the focus after you've changed the framing with the zoom ring.

Anyone else observe this behavior ?

I owned this lens a while back and don't remember this 'feature'. Is it a new firmware feature or something weird going on with my lens ?




Sep 06, 2017 at 12:34 AM
leighton w
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p.1 #2 · p.1 #2 · Fuji 50-140 f2.8 automatically refocus or parafocal feature ?


millsart wrote:
Just noticed something on my 50-140 f2.8. If I lock focus on a subject, and then turn the zoom ring, the lens will automatically adjust the focus. The lens optically is not parafocal, meaning that you can focus at one focal length and keep the subject in focus if you then turn the zoom ring, most lenses aren't these days. Never really noticed before that the lens and/or camera body seems to be trying to adjust the focus after you've changed the framing with the zoom ring.

Anyone else observe this behavior ?

I owned this lens a while back and don't
...Show more

Either way, it sounds like a good thing.



Sep 06, 2017 at 10:03 AM
mdude85
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p.1 #3 · p.1 #3 · Fuji 50-140 f2.8 automatically refocus or parafocal feature ?


millsart wrote:
Just noticed something on my 50-140 f2.8. If I lock focus on a subject, and then turn the zoom ring, the lens will automatically adjust the focus. The lens optically is not parafocal, meaning that you can focus at one focal length and keep the subject in focus if you then turn the zoom ring, most lenses aren't these days. Never really noticed before that the lens and/or camera body seems to be trying to adjust the focus after you've changed the framing with the zoom ring.

Anyone else observe this behavior ?

I owned this lens a while back and don't
...Show more

As far as I know, all XF lenses are varifocal (focal plane changes as you zoom), so any parfocal 'effect' you might notice is going to be controlled by the AF system, not the lens itself. I don't think the AF system has a true parfocal capability, it is likely just refocusing very quickly after you zoom.



Sep 06, 2017 at 06:11 PM
millsart
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p.1 #4 · p.1 #4 · Fuji 50-140 f2.8 automatically refocus or parafocal feature ?


Its interesting though that it automatically refocuses, without telling it it. My 18-55 by comparison doesn't do this, but that lens also doesn't show as much change of focus when you zoom.

What I can't tell is if zooming the lens, after you've locked focus, just automatically causes the lens to refocus, OR, if there is some algorithm that shifts the focus a given amount, for a given change in focal length and given focal distance.

Reason I wonder, is that if I put the AF point on a contrasty subject, on a white wall, and then move the focus point off that subject, when I turn the zoom ring the lens still adjusts the focus so the subject is sharp, even though the AF point is no longer on the subject. If the lens was simply activating the AF system again I don't think it would find focus, because I can't otherwise focus on such a low contrast subject when testing it.

As such, it seems like some sort of automatic adjustment process the lens performs.



Sep 07, 2017 at 02:51 AM







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