An U.P. workshop has been in the works for a couple of years now and
I've researched a lot of locations in "Copper Country."
The main reason why an internal-focus lens loses less light during
close focusing is two-fold. One reason is the lens will shorten in
focal length. The other reason is that depending on design, the
focusing is done by optically moving the rear nodal point through the
adjusting of lens elements in relationship to other lens elements,
whereas a traditional lens physically moves the rear nodal point by
physically moving the lens away from the film or sensor.
AG
On Thursday, December 16, 2010, <usher99@xxxxxxx> wrote:
>>But then I went to Wiki looking for some support for my supposition and
>> see that it's far more complicated than I thought. For macro work it
>> says that DOF is better thought of in terms of magnification and focal
>> ratio which then makes DOF (almost) independent of focal length.
>
> Well Chuck I think is correct, but then he has Dr. Focus as an in house
> consultant.
> At least with the Z. 80mm macro pupil magnification is not an issue as
> it is symmetric.
> This link I think helps a tad:
> http://toothwalker.org/optics/dof.html
> See about 2/3 way down--pupil magnification is not terribly mysterious.
>
>
> Now what happens with light loss and DOF when the floating elements
> move in macro lenses??
> That is mysterious to me. John Shaw claims less light loss than pure
> extension.
> Hmm, I should check with the CV125 apo Lanthar macro--I have enough
> extension to do that with the auto tube etc.
> Only Dr. Focus would be interested though.
>
> Mike
>
> PS Perhaps AG should try for a workshop in the UP--but only when it is
> MUCH warmer--unless I get to use the 3T that is.
> --
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>
--
Ken Norton
ken@xxxxxxxxxxx
http://www.zone-10.com
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