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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