Re: TECH3D digest 61

[T3D Eric Goldstein <egoldste@xxxxxx>]

BobH say:

> In the old days, one measured from the closeup lens..or if trying to
> be more accurate from about where the diaphragm was located or some
> other "center" of the lens.
> When SLR came in with bulky auto-diaphragm lenses and helical mounts,
> the glass in the lens was hard to find....

JohnB say:

> According to my measurements, the front focus just about lands on the
> closeup lens.  The primary nodal point will be 50 mm back of that since
> the combination focal length isn't affected by the closeup lens if the
> closeup lens is located at the front focus.  So the primary nodal point
> is going to fall at about the juncture of lens body and camera body.

Come to think of it, I used to do a lot of panaramas through
compositing, but did have difficulty finding the right spot to pivot
around with SLRs. As most of my close focus work is at +1 or +2, I guess
I'm still working with enough DOF to cover the difference between the
film plane and the actual RNP.

How about retrofocus wide lenses, John, like canon 24, 28 or 35 mms?

Eric G.


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