So how do they re-calibrate a lens?

gramps

gramps

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I have a S/H zoom lens that I will be sending to Fixation, as it appears to be focusing ahead of the subject and in-camera micro-adjust cannot seem to resolve it.
Does anyone know what will actually be done to the lens in order to correct the focus adjustment and bring it back to within Nikon's acceptable range?
 
I think it's a mixture of black magic and voodoo :D

Merry Chrimbo Gramps :)
 
Ha ... I'm seriously hoping that there's more to it than that Steve :D
 
In the absence of specific Nikon answers I'll give the Canon approach.

Assuming that there's not a mechanical problem then the calibration is achieved by adding or cutting wire links to give an offset to the focus encoder....BFCV links (Best Focus Correction Value).

Bob
 
Are you sending the camera with the lens? It may well be in "acceptable range" on another body..... Missing focus is one of the key reasons I moved to CSCs.
 
arad85 said:
Are you sending the camera with the lens? It may well be in "acceptable range" on another body..... Missing focus is one of the key reasons I moved to CSCs.
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No ... I recently had the D800 confirmed with Nikon UK to be 'within spec' and I get the same problem when using the D3s and it's only this lens.
I have tried using 'micro-adjust' + Spyder Lenscal with both cameras but there just isn't enough adjustment to get it anywhere near 'spot-on', hence why I'm assuming that it needs the re-calibration.

Incidentally, I think I'm now going to be unsure of any answer as to 'what they do' in this thread :thinking:
 
Phase detection is quick but not especially accurate. It is rather like trying to kick a ball with exactly the right speed to stop exactly on the goal line. Even when properly calibrated it has a fairly wide Probability factor. No two attempts at focus are identical. ( but are mostly within the makers acceptability range. This is usually stated as a proportion of the depth of field)

Contrast detection is rather slower as it is not so much predictive as iterative but it is more accurate as a result.

The newer on sensor Hybrid systems, utilising phase and contrast detection, seem to be far superior in principal, and this seems to be born out in practice.
Some CSC units are now both faster and more accurate for single shots, than DSLR's. Though as yet they do not seem to have the calculating capacity for Predictive focussing.

Of course Predictive focus is always a best guess and never a measured result, so always has a "chance" factor.

The Mechanical factor of a Phase detection unit on a DSLR having to rely on a set of mirrors adds a further opportunity for lack of standardisation and error.
 
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I am no expert but I thought there were micro screws or something in the lens that can be adjusted........... Maybe I just dreamed that. :wacky:
 
gramps said:
I have a S/H zoom lens that I will be sending to Fixation, as it appears to be focusing ahead of the subject and in-camera micro-adjust cannot seem to resolve it.
Does anyone know what will actually be done to the lens in order to correct the focus adjustment and bring it back to within Nikon's acceptable range?
Click to expand...

To answer your question - calibration may involve moving around a few lens elements until everything sings.

On the other hand you seem to have purchased a real duffer. I would try to get the money back in the first instance (you don't want to poor in money repairing faulty or knocked lens) and buy somewhere more reliable, even ebay.
 
Nikon AF-S lenses are physically autofocussed by the Silent Wave Motor - there are two types of SWM, the compact type and the more expensive ring type. We don't know if the motors are adjusted mechanically during calibration - or if they just use software to change how the motor reacts to the signal coming from the camera's Phase Detect sensor. Perhaps their technical bods would spill the beans.

Some interesting pics/info here:

Phase Detect sensor - http://www.dpreview.com/reviews/NikonD3s/Images/afmodule.jpg
Compact (Mini DC) type SWM - http://www.microglobe.co.uk/cimages/swm.JPG
Ring type SWM (top in pic) - http://cdn-4.nikon-cdn.com/en_INC/I...KOR-300mm-f-4D-IF-ED/Misc/SWM_description.jpg


According to this link, a lens fitted with the compact SWM will have 8 contacts and a lens fitted with the ring SWM will have 10 (I'm not sure if this is true or not) - http://www.clubsnap.com/forums/showthread.php?t=775275
 
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Ozei said:
Nikon AF-S lenses are physically autofocussed by the Silent Wave Motor - there are two types of SWM, the compact type and the more expensive ring type. We don't know if the motors are adjusted mechanically during calibration - or if they just use software to change how the motor reacts to the signal coming from the camera's Phase Detect sensor. Perhaps their technical bods would spill the beans.

Some interesting pics/info here:

Phase Detect sensor - http://www.dpreview.com/reviews/NikonD3s/Images/afmodule.jpg
Compact (Mini DC) type SWM - http://www.microglobe.co.uk/cimages/swm.JPG
Ring type SWM (top in pic) - http://cdn-4.nikon-cdn.com/en_INC/I...KOR-300mm-f-4D-IF-ED/Misc/SWM_description.jpg


According to this link, a lens fitted with the compact SWM will have 8 contacts and a lens fitted with the ring SWM will have 10 (I'm not sure if this is true or not) - http://www.clubsnap.com/forums/showthread.php?t=775275
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Thanks, some very useful information - this lens uses the ring type SWM it seems so that at least appears to be good. :)


daugirdas said:
To answer your question - calibration may involve moving around a few lens elements until everything sings.

On the other hand you seem to have purchased a real duffer. I would try to get the money back in the first instance (you don't want to poor in money repairing faulty or knocked lens) and buy somewhere more reliable, even ebay.
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Thanks, if it was a new lens or high-priced S/H I might well ask for my money back but buying S/H is often a case of accepting some limitations, be it no warranty, a scratch or an adjustment needed - in this instance I am happy to have it adjusted on the basis of S/H prices at the time of purchase :)
 
daugirdas said:
On the other hand you seem to have purchased a real duffer. I would try to get the money back in the first instance (you don't want to poor in money repairing faulty or knocked lens) and buy somewhere more reliable, even ebay.
Click to expand...

Actually you were right, the report says that it has suffered 'impact damage' and will cost a significant amount to repair - this is definitely a purchase I sorely regret.
 
I haven't accepted the estimate ATM Carl and am in touch with the seller - but it is a hefty figure at almost 1/3rd the cost of the lens!
 
Steve Smith said:
Nonsense. It's done with a set of calibration hammers.
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I have seen movie camera zoom lenses (Angenieux) have the zoom tracking adjusted with the aid of a small hammer to make matching pairs for Stereoscopic 3D.
 
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