Sigma 70-210 1:2.8 APO advice (please)

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twills99

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Tim
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Hi all,
I have a Nikon fit Sigma 70-210 APO 1:2.8. The lens is a few years old, but in fantastic condition, and takes beautiful contrasty shots.
However, I have noticed that when wide open, it 'front focuses' a good deal (more than a few inches). I suspect it is also doing this when stopped down, but not so evident. It focuses fast and positively - just not accurately!
On manual it is pin sharp at all F stops.
Any advice on adjustment would be appreciated. The body is perfect with all other lenses. Does anyone know of a fix or is it only something that Sigma could adjust?

Thx
 
I'd be surprised if Sigma UK would touch such an old lens - the usual trick to fix this would be to "shim" it.

There is something a bit "odd" with old x0-200mm on digital bodies from the film era - Nikon has a warning abo ut focus problems with the 80-200 f/2.8 AF and Tokina can't service their 80-200 f/2.8 AT-X Pro to focus correctly on digital bodies. Thats direct from the horse mouth (THK)

All I can guess that these lenses were optimised for film and possibly were caliberated to work with cellulose of varying thickness.

TBH I doubt it it would be economical to fix - chances are if you put the lens on a film body, it would be spot on.
 
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Thanks Andy,

Do you know where I could get info on 'shimming' please? Seems a shame as it is a wonderful lens to use - I suppose if all else fails it makes a good MF lens..
 
"Shimming" is a technique whereby thin circles of metal (very very thin) are stacked to allow minute adjustments of lens elements.

If you have a Nikon 18-200 VR, unscrew the front element, and 3 or 4 silver 72mm silver rings will fall out. (these are "shims", the number of "shims" will depend on the lens).

(I suggest the 18-200 VR as its dead easy to remove the front element)
 
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