Sigma 17-50mm 2.8 barrel wobble?

wowarning · 06-03-2014, 08:43 PM

Just purchased a used copy of this lens from the marketplace and was wondering if anyone who currently owns it can help me figure out if some barrel wobble is normal for this particular zoom. Fully extended it probably rocks back and forth about 1mm which is enough to see the angle of the front element change. It is present at the short end as well but is slightly less pronounced due to the geometry of a shorter extension. When positioned horizontally the play is always present only in the upward direction making me think that the barrel may be 'drooping' when in a shooting position and could cause decentering or focus issues. I have not yet had a chance to perform tests with the lens on the camera, but will do so shortly. Can anyone shed some light on whether I'm being a nervous Nelly, or if this is a reason for concern? Much thanks in advance. (Come to think of it - any advice on how to test for decentering would be helpful as well, lol.)

Steve.Ledger · 06-03-2014, 08:51 PM

Ha.. I just got the 18-55mm WR with my K-50, the barrel wobbles more than 1mm, especially exaggerated with the hood on. Doesn't seem to affect photos though.
I think the internal lens/elements tolerances are far more important than that first one.

OregonJim · 06-03-2014, 11:16 PM

Originally posted by Steve.Ledger

I think the internal lens/elements tolerances are far more important than that first one.

The front element is critical in equalizing the angle of incidence with the angle of refraction. That's easy with primes, but is always a compromise with zooms, whick makes its alignment even more critical there. Check out Snell's Law if you're interested.

The question is, does it cause any observable abberation in this case? Only the OP can answer by doing some controlled testing.

I would try several shots on a tripod of a flat but textured surface (e.g. brick wall). Try some at close focus, some at midrange. The trick will be to hold the barrel at different "wobble" angles without introducing camera shake. Bright room or flash with high shutter speeds will help. It may get tedious, as the process should be repeated throughout the zoom range.

I don't expect that 1mm of travel will produce any discernable abberations in a focal length less than 100mm, but I could be wrong.

Steve.Ledger · 06-04-2014, 01:03 AM

I don't think 1mm is going to turn your lens into a tilt-shift

So long as it's not wobbling in the breeze while you're shooting just go out, take photos enjoy life a bit, there's more important stuff to be pernickety about..

OregonJim · 06-04-2014, 08:07 AM

Originally posted by Steve.Ledger

I don't think 1mm is going to turn your lens into a tilt-shift

Moving just the front element does not a tilt-shift lens make.

wowarning · 06-04-2014, 09:26 AM

Thanks guys. Can anyone with this lens say if their copy is wobbly, rock solid, or somewhere in between?

06-03-2014, 08:43 PM	#1
wowarning Forum Member Join Date: Jun 2013 Posts: 60	Sigma 17-50mm 2.8 barrel wobble? Just purchased a used copy of this lens from the marketplace and was wondering if anyone who currently owns it can help me figure out if some barrel wobble is normal for this particular zoom. Fully extended it probably rocks back and forth about 1mm which is enough to see the angle of the front element change. It is present at the short end as well but is slightly less pronounced due to the geometry of a shorter extension. When positioned horizontally the play is always present only in the upward direction making me think that the barrel may be 'drooping' when in a shooting position and could cause decentering or focus issues. I have not yet had a chance to perform tests with the lens on the camera, but will do so shortly. Can anyone shed some light on whether I'm being a nervous Nelly, or if this is a reason for concern? Much thanks in advance. (Come to think of it - any advice on how to test for decentering would be helpful as well, lol.)

06-03-2014, 11:16 PM	#3
OregonJim Veteran Member Join Date: Mar 2009 Location: Willamette Valley, Oregon Posts: 1,327	Originally posted by Steve.Ledger I think the internal lens/elements tolerances are far more important than that first one. The front element is critical in equalizing the angle of incidence with the angle of refraction. That's easy with primes, but is always a compromise with zooms, whick makes its alignment even more critical there. Check out Snell's Law if you're interested. The question is, does it cause any observable abberation in this case? Only the OP can answer by doing some controlled testing. I would try several shots on a tripod of a flat but textured surface (e.g. brick wall). Try some at close focus, some at midrange. The trick will be to hold the barrel at different "wobble" angles without introducing camera shake. Bright room or flash with high shutter speeds will help. It may get tedious, as the process should be repeated throughout the zoom range. I don't expect that 1mm of travel will produce any discernable abberations in a focal length less than 100mm, but I could be wrong. Last edited by OregonJim; 06-03-2014 at 11:34 PM.

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06-03-2014, 08:51 PM	#2
Steve.Ledger Veteran Member Join Date: Oct 2009 Location: Far North Qld Posts: 3,301	Ha.. I just got the 18-55mm WR with my K-50, the barrel wobbles more than 1mm, especially exaggerated with the hood on. Doesn't seem to affect photos though. I think the internal lens/elements tolerances are far more important than that first one.

06-04-2014, 01:03 AM	#4
Steve.Ledger Veteran Member Join Date: Oct 2009 Location: Far North Qld Posts: 3,301	I don't think 1mm is going to turn your lens into a tilt-shift So long as it's not wobbling in the breeze while you're shooting just go out, take photos enjoy life a bit, there's more important stuff to be pernickety about..

06-04-2014, 08:07 AM	#5
OregonJim Veteran Member Join Date: Mar 2009 Location: Willamette Valley, Oregon Posts: 1,327	Originally posted by Steve.Ledger I don't think 1mm is going to turn your lens into a tilt-shift Moving just the front element does not a tilt-shift lens make.

06-04-2014, 09:26 AM	#6
wowarning Forum Member Join Date: Jun 2013 Posts: 60 Original Poster	Thanks guys. Can anyone with this lens say if their copy is wobbly, rock solid, or somewhere in between?