In article <4vavcd$r18@mtinsc01-mgt.ops.worldnet.att.net>, TwoCybers@postoffice.worldnet.att.net says...

>I have an N90s and a Nikor 105 macro lens. I would like to increase
>the reproduction ratio.
>I was going to order the PN-11 extension tube which I understand is 52
>mm. The instruction manual for the 105 lens states that the auto
>extension ring PK-11 should not be attached to this lens and that the
>PK-11A should be used instead. The PK-11A is 8 mm. I have never seen
>a PK-11 advertised or referenced in the literature.
>Is the PK-11 the same as the PN-11? If so, why would the 8 mm PK-11A
>be the replacement for the 52 mm PN-11?

They are different tubes. The long PN-11 works fine (as does the TC201
converter, at smaller stops). The PK-11 should not be used on AF
bodies due to interference problems with the electrical contacts. The
replacement PK-11A was changed to allow its use with AF bodies/lenses,
though there is no feed-through of electrical info or the AF shaft.
Hope This Helps