On 4/20/2010 4:28 PM, usher99@xxxxxxx wrote:
> ...
>
> Moose's comment about the relationship between MFD, FL and mag at 1:1 is
> quite cool--never seen it expressed that way---clearly is correct and a
> really neat thing to know. Thanks!!
>
I thought everybody knew that. ;-)
> Closest I got to the algebra to prove it is 2F=G at 1:1 but g is only the
> distance form lens to subject and doesn't include MFD from focus plane to
> subject.
1/S1 + 1/S2 = 1/f - The thin lens formula
M = 1 = S1/S2 - The magnification formula applied to 1:1
.: S1 = S2
2/S1 = 1/f
S1 = 2f
S1 + S2 = 4f
> Too tired to try right now, it is clearly correct. Must measure with Big
> Foot at 1:1 as it uses a combo of standard extension and floating
> elements--down side of straight extension is loss of light of course.
>
I agree with Wayne. It doesn't matter how the magnification is achieved,
the inverse square law applies.
Moose
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