12-19-2016, 06:12 PM
Well the lens is returned and refunded, the owner was straight on route to the shop where it was purchased, who are sending it back to Sigma.
Thoughts and possibilities of the causes of lens de-centering:
1, Displaced elements which are not properly seated in their appropriate locations at the point of manufacture;
2, Couplets triplets or whatever groups of elements which have been cemented in a poorly aligned fashion.
3, A shock or knock which has unseated one or more of the elements. Impacted plastic/metal lens tubes which have been distorted and are no longer aligned with the axis of the lens's main body, as sometimes is seen when a lens has been dropped and landed on the front filter ring.
4, The optical stabilization element not floating in it's correct neutral position.
5, Bayonet mounts which have been distorted from a shock or forced poor mounting.
6, Wear from extensive usage over time. (this happens with cheaper plastic lenses)
I'm sure there are a few other reasons to add to this.
From my own lens buying experiences, the most problems I have encountered ( I would say more than 60%) the most frequent incidence is "when buying from new". By far the most problems are at that point of sale, mostly having been delivered in undamaged packaging.
Is it really possible that a lens can receive a sufficient shock to mis-align lens elements without any sign of damaging to the box? It is a posibilty I suppose, but......Hmmm...mostly I just don't buy it!
Remember the lens is delivered in it's well padded lens case inside the cardboard packing, few lenses have the benefit of this sort of shock resistance!
The second highest is from S/H lenses which have no apparent sign of having suffered any sort of shock, ie, filter thread impacts or other. I also have had my fair share of those, mostly though have been older Tamron/ Pentax/Sigma or Nikon AF-D zooms.. Again I think most were always like that! With the exception of an AF35-70 F2.8D which had de-lamination issues with the plastic optical element.
Lenses that clearly have received an impact, bent or broken filter rings being the most common, some there are duds, yet often the lenses are optically fine.
My Nikon AFS70-300mm VRII I think has suffered an impact or has been dropped, the AF was snagging inside which i repaired and the VRII system plays strange games where the image in the viewfinder drops excessively drops when it sleeps, yet, it's perfectly centered (with activated VR) . I now only have one de-centered lens and that is the Nikor AFs18-105 VR, the rest are fine.
The really old MF aluminium lenses are mostly fine, at least I've never had a dud.
In short, just from my experiences....IMHO most de-centered lenses left the factory gates like that mainly from reason number two.
P.S. I have never had a lens which has developed de-centering for whatever reason, once good they stay good, I've even dropped a couple.
Thoughts and possibilities of the causes of lens de-centering:
1, Displaced elements which are not properly seated in their appropriate locations at the point of manufacture;
2, Couplets triplets or whatever groups of elements which have been cemented in a poorly aligned fashion.
3, A shock or knock which has unseated one or more of the elements. Impacted plastic/metal lens tubes which have been distorted and are no longer aligned with the axis of the lens's main body, as sometimes is seen when a lens has been dropped and landed on the front filter ring.
4, The optical stabilization element not floating in it's correct neutral position.
5, Bayonet mounts which have been distorted from a shock or forced poor mounting.
6, Wear from extensive usage over time. (this happens with cheaper plastic lenses)
I'm sure there are a few other reasons to add to this.
From my own lens buying experiences, the most problems I have encountered ( I would say more than 60%) the most frequent incidence is "when buying from new". By far the most problems are at that point of sale, mostly having been delivered in undamaged packaging.
Is it really possible that a lens can receive a sufficient shock to mis-align lens elements without any sign of damaging to the box? It is a posibilty I suppose, but......Hmmm...mostly I just don't buy it!
Remember the lens is delivered in it's well padded lens case inside the cardboard packing, few lenses have the benefit of this sort of shock resistance!
The second highest is from S/H lenses which have no apparent sign of having suffered any sort of shock, ie, filter thread impacts or other. I also have had my fair share of those, mostly though have been older Tamron/ Pentax/Sigma or Nikon AF-D zooms.. Again I think most were always like that! With the exception of an AF35-70 F2.8D which had de-lamination issues with the plastic optical element.
Lenses that clearly have received an impact, bent or broken filter rings being the most common, some there are duds, yet often the lenses are optically fine.
My Nikon AFS70-300mm VRII I think has suffered an impact or has been dropped, the AF was snagging inside which i repaired and the VRII system plays strange games where the image in the viewfinder drops excessively drops when it sleeps, yet, it's perfectly centered (with activated VR) . I now only have one de-centered lens and that is the Nikor AFs18-105 VR, the rest are fine.
The really old MF aluminium lenses are mostly fine, at least I've never had a dud.
In short, just from my experiences....IMHO most de-centered lenses left the factory gates like that mainly from reason number two.
P.S. I have never had a lens which has developed de-centering for whatever reason, once good they stay good, I've even dropped a couple.
