Can a lens maintain focus while zooming?

R

Ripple

Member
According to Bary Green,

"Still-camera lenses aren't parfocals, they don't hold focus at all. If you tried to use an SLR to zoom in, focus, and zoom back out, you'd find your shot is probably terribly out of focus..."
http://www.dvxuser.com/articles/article.php/26

I asked an someone about this who is a former pro sports photographer, and who has shot video with a 5D Mk. II, 7D, and 1D Mk. IV. He said lenses do indeed hold focus while zooming.

I doubt either the author of the article or the sports photographer is exactly correct or incorrect, just probably something I'm not getting here. Can someone please explain?

BTW, the lens I'm most interested in is the EF 24-105mm f/4L IS USM, but I don't know if that's relevant.

Thanks.
 
I have a Nikon 80-200 f/2.8 - it's great because you can focus the shot and then zoom to any focal length you like and it keeps perfect focus !

So that's one for the "some still lenses are parfocal" camp.
 
Some are parfocal, many are not. It's not usually an issue with still lenses, and it costs more money to do them that way, so most manufacturers don't do it apparently.
 
most quality lens will keep focus if you start wth the aperture as open as possible . with a zoom that would most likely be 2.8 zoom to max to focus pull back to frame set f stop to what ever is called for . this works best for primes but if you zoom and focus at a higher f stop the focus will not be as accurate and might show up as soft when traveling through the zoom range . quality glass is expensive for a reason . A great monitor helps a ton ,i like my Manhattan lcd 8 in hd 720p .
 
I think it depends on the lens and its vintage. Paradoxically older manual focus zooms are likely to be true zooms rather than varifocal.
The advent of autofocus meant that designers could become lazy and let the focus go hang.
You could try zooms from Leica (R-glass) or Contax.
I think my 24-105 L Canon zoom isn't parfocal.
Dave
 
I wish the 24-105L was parfocal...

I wish the 24-105L was parfocal...

Lee Wilson, PerroneFord, and jetaddiction:

Thanks for your time. Looks like it just depends on the lens.
daveswan said:
...I think my 24-105 L Canon zoom isn't parfocal.
Click to expand...
That's a shame because this lens would cover 90% of what I would want for photography and video, and there doesn't appear to be a Nikon equivalent (for when Nikon introduces 1080p video).
 
I've heard it said that the 24-70 f/2.8 does hold its focus, but it's considerably more expensive and shorter range.
Funny thing is, I've still got an old (Ca 1978) Vivitar 35-105 f/3.5 that does hold its focus and is built like a tank, no plastic anywhere, but it's FD fitting, and was regarded as a rather soft budget zoom, even then. Mind you I may see if I can find one in F fitting and use an adapter, It should only cost about £50 or less.
Dave
 
The test is to zoom fully in, focus, then zoom out. If the image is still sharp, the lens tracks fine. Don't forget that even on the best lenses if you focus on wide, it's almost bound to go out on the zoom in. Depth of field on a narrow angle is smaller than when it's one wide.
 
Ripple said:
Lee Wilson, PerroneFord, and jetaddiction:

Thanks for your time. Looks like it just depends on the lens.

That's a shame because this lens would cover 90% of what I would want for photography and video, and there doesn't appear to be a Nikon equivalent (for when Nikon introduces 1080p video).
Click to expand...


My experience of this lens is that it does indeed hold focus.
 
daveswan said:
I think it depends on the lens and its vintage. Paradoxically older manual focus zooms are likely to be true zooms rather than varifocal.
The advent of autofocus meant that designers could become lazy and let the focus go hang.
You could try zooms from Leica (R-glass) or Contax.
I think my 24-105 L Canon zoom isn't parfocal.
Dave
Click to expand...

My experience of this lens is that it does indeed hold focus.
 
Hmm... well mine does appear to be parfocal, but that's checking it indoors.
So I'll give you that one and admit I was wrong.
Dave
 
Is the Canon EF 70-200mm f/4L IS USM a parfocal?

Is the Canon EF 70-200mm f/4L IS USM a parfocal?

yoclay and daveswan:

Many thanks for checking out the 24-105 f/4L. This is the next one I want.:thumbsup:

BTW, anyone here know if the EF 70-200mm f/4L IS USM is a parfocal? Nikon makes its share of great glass, but no equivalent to this lens either...
 
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