Sun 04-Nov-12 08:05 AM | edited Sun 04-Nov-12 08:06 AM by blw
Rank C generally requires nearly complete disassembly, and is pretty much by definition a labor intensive situation. What else was on the invoice? And what lens was involved?
Nikon's policy is to return the item to full specification, but not necessarily to visually new condition. So they will probably not change an element if it has a tiny nick on it, but they will if it has an optically visible scratch or significant loss of coating. They don't replace a scratched lens barrel, unless the scratch is somehow on the inside where it might reflect light and create internal flare.
Replacing a helicoid, particularly a zoom helicoid, can be a pretty extensive operation. The zoom group(s) would be mounted or at least contained in this helicoid, so replacing it would require removal of all associated elements and recalibrating their positions. Most zooms also have at least some electronics associated with them (if only to provide focal length EXIF data). Furthermore, some zoom helicoids also cause the focus group to move, and in these cases nearly the entire lens has to come apart to replace a zoom helicoid. For a complex lens such as a 200-400/f4 AFS VR, as many as 16 or 17 lens elements may be involved. And actually nearly all of the zooms are now getting very complex: even "simple" lenses like the 16-85VR have 17 elements in 11 groups. (The 200-400 has 24 elements.)
Even if the helicoid is a focusing helicoid, it depends on which lens it is. The focusing helicoid in the famous 105/f2.5 AI is very simple; I'm pretty sure only one element is moving. (There are only five, in four groups.) On the other hand, the focusing helicoid on the 400/f2.8 AFS moves a far larger element a much greater distance - and modern lenses have all of the auto focus mechanisms entangled in the workings of the helicoid.
_____ Brian... a bicoastal Nikonian and Team Member
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