nodal points

["Hay, Brian" <hayb@xxxxxxxxxxxxx>]

Dear Pan Group

I would really appreciate some advice on a topic that to many of you may
seem child's play; namely, how on earth do I determine the nodal point
of a lens?  My plan is the not unusual trick of mounting my camera
(portrait or vertical position) on an L-mount on my tripod, with some
sort of mechanism, (yet to be determined) that will allow me to position
the camera so that the nodal point is fore-and-aft, left-and-right,
directly over the pivotal centre of the tripod.  The problem is I have
no real idea on what the nodal point means!  I thought it was the front
plane of the mounted lens but now I'm not so sure.  Any advice I can get
on setting it and on a mechanism for helping me mount the camera
accordingly, would be much appreciated.

Many thanks
Brian Hay
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