Zoom Nikkor 28-85 f3.5-4.5 AI-S - seized at 50mm

First time poster, and apologies for starting my career here with a request for help. I hope to be around for a while and to contribute actively in future.

I was hoping I might be able to benefit from someone's experience. This concerns a Nikon 28-85mm AI-S zoom that appears to be seized at lengths above 50mm.



(Image from the Photography in Malaysia site.)

I recently picked up the above lens for a small amount from a charity shop. It appears practically unused, but appears to have a problem. It zooms smoothly throughout the range from 50mm to 28mm, including the macro setting accessed by rotating a third collar, but won't go above 50mm at the longer end.

It effectively has a hard stop at exactly 50mm, preventing any movement from there to longer focal lengths. A visual inspection from both ends of the lens doesn't show any obvious problems, but there are clearly many elements and actions inside the lens which aren't visible from merely peering in.

Is anyone aware of any common (and ideally easily fixed) problems with this lens? I rarely use zooms and am prepared to put this down to experience, but if it's easily fixed, or if I'm simply missing something in the operation of the lens, I'd be glad to be able to use it.

In hindsight, the lens is in such good condition - practically NOS - that I'm starting to wonder if it had this fault from very early on, hence the obvious lack of use.

Any comments (other than caveat emptor, which goes without saying!) very welcome.

Zoom lenses have a complicated inner cam mechanism. I would not advise attempt of repair or even investigation without prior experience with lenses of fixed focal length.

I got a near mint 70-210mm with a similar issue (likely a defect along one of its cam slits). I use it in the resting range. Of course on should check if at least that range is working properly concerning image quality.
Mine can to be substituted for little money, thus I likely even will not start repair.

Thanks. I think putting it down to experience seems like the most likely outcome, although I may strip it down out of curiosity. Whether the lens is achieving reasonable quality between 28mm and 50mm is neither here nor there really; I'd rather stick to a lighter, faster prime than carry around a comparatively heavy, slower zoom with a severely restricted range.

Assuming you got it cheap from a charity shop it's worth having it serviced by a professional, or at least getting a quote, because this is a very useful range walk around lens that's too good quality to discard.

Common causes for all zoom lenses are broken or loose rollers in the cams.

I have this exact same model lens since new and the zoom ring should move freely from 28 to 85 at all times (except macro of course). It may be worth getting repaired; the focal lengths are useful enough.

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