Why Canon 24-105 changing focal length?

[kevs]

Has anyone seen this, or maybe I'm going crazy. I have this L lens at 24, and I focus on a few different subject in the studio (just focusing, nothing else), and it seems that the lens goes from 24 to 50. 

[BernardLanguillier]

You have managed to buy the only available sample of the motorized zoom version of this lens!

Not helping, I know.

Cheers,
Bernard

[pegelli]

Just to be sure I understand your question: Is your lens really zooming to 50 mm field of view, or is the focal length in the exif changing to 50 mm while still at 24 mm field of view.

In case of the former, is the zoom ring turning to the 50 mm setting or remaining in the 24 mm position.

Depending on which scenario happens the cause will probably be different.

[kevs]

I'm just focusing and yet it's going from 24 up to 50, 60. Puzzled.

[ThePhotoDude]

This is focus breathing on steroids! (Also not helping, sorry)

[chez]

The lens is notorious for zoom creep. Maybe that is what is occurring.

[francois]

The lens is notorious for zoom creep. Maybe that is what is occurring.

If it's zoom creep then I've experienced that on both a friend's 24-105 and my 24-70. I sent my 24-70 in for repair and zoom creep was fixed.

[kevs]

Thanks Chez and Francois!

Zoom creep, never heard of it, ever, wow and on an L lens. (and it's known issue!)

Ok, I'll keep testing and get a repair if needed, not looking forward to that bill, you would think they would have solved something like that by now?

[John S C]

Had a similar problem with my lens ,I lived with it for a while 'till the lens developed a problem that required a repair. Mentioned the problem to Canon, and the technician who repaired the lens used a slightly thicker lubricant on the mechanism, which cured the problem

[Harold Clark]

My 24-105 changes focal length when doing aerials, the pressure of the wind against the lens is all it takes. I now keep a firm grip on the zoom ring when shooting aerials.

[Misirlou]

The 24-105 is not a true zoom Originally the definition of zoom lens required that as focal length changed, focus did not. The 24-105, like a lot of modern "zooms," has an interactive relationship between focus an focal length. If you reframe a shot with the zoom collar, you have to refocus as well, and vice versa. I'm just guessing, but that interactivity between the controls might be what you're seeing.

Incidentally, I used to have a couple of true zooms for 35mm in the film days. I actually liked the "push-pull" zoom controls that were common on those lenses in the 80s, mostly because you could do everything without moving your fingers from one part of the lens to another. But from what I gather, most people did not like them, because there was always a chance you'd change focus as you zoomed. With something lie the 24-105, a push-pull layout would be more useful, if you're trying to do manual focus.

[Robert55]

IMHO describing parfocal lenses as 'true' zooms is rather quaint and I doubt the quality of being parfocal is part of the original definition of a zoom lens.
But I guess this is not the problem the OP is describing anyway

[Glenn NK]

Thanks Chez and Francois!

Zoom creep, never heard of it, ever, wow and on an L lens. (and it's known issue!)

Ok, I'll keep testing and get a repair if needed, not looking forward to that bill, you would think they would have solved something like that by now?

Don't waste your time and money - there is nothing to repair.   Many of them do it, and from what I've read on forums, I think only a small percentage don't.  Mine was creeping from day one eight years ago.

One of the older zooms (100-400) has a zoom creep adjustment - the ease of movement can be adjusted (it's a push/pull zoom).

My EFS 17/55 also creeps a bit.  One learns to hold the zoom ring in the left hand when shooting "uphill or downhill".

Glenn

[digitaldog]

The 24-105 is probably my most used (walk around) lens. I must be lucky, I've never seen this but have heard reports of similar from other lens.

[Misirlou]

IMHO describing parfocal lenses as 'true' zooms is rather quaint and I doubt the quality of being parfocal is part of the original definition of a zoom lens.
But I guess this is not the problem the OP is describing anyway

Whatever. "A true zoom lens, also called a parfocal lens, is one that maintains focus when its focal length changes. A lens that loses focus during zooming is more properly called a varifocal lens...Many so-called "zoom" lenses, particularly in the case of fixed lens cameras, are actually varifocal lenses, which gives lens designers more flexibility in optical design trade-offs (focal length range, maximum aperture, size, weight, cost) than true parfocal zoom, and which is practical because of autofocus, and because the camera processor can move the lens to compensate for the change in the position of the focal plane while changing magnification ("zooming"), making operation essentially the same as a true parfocal zoom."

Apparently the first true zoom was patented in 1902.

From Wikipedia.