Re: [OM] Extension Tubes

[Chuck Norcutt]

Good.  You've got it!  I guess we'd better get those +0.5 diopter lenses 
while we can.  :-)
Chuck Norcutt


On 5/13/2016 4:20 PM, Chris Trask wrote:
>      Doing the math as an estimate, letting f be an "equivalent registry 
> distance", I find that the extension tube needed to equate to a +0.5 diopter 
> close-up auxiliary would be 3.154mm thick, which is close to my earlier thumbnail 
> guesstimate.
>
> > f is simply the focal length of the lens.  When an object is at infinity
> > the image is formed at distance = the focal length.
> >
> > S1 is the object distance from the lens and S2 is the distance to the
> > image formed by the object.  If S1 = infinity then S2 = f.  As the
> > object comes closer the image distance starts increasing until when S1 =
> > f then S2 will equal infinity.
> >
> > But all of these distances are relative to the optical center of the
> > lens.  Not easy to determine in a modern lens.
>
> Chris
>
> When the going gets weird, the weird turn pro
>      - Hunter S. Thompson
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