.From: <frankrad4@xxxxxxxx>
> Does anybody know what the added extension is on the 90/2 when it is
> focused all the way out on the helicoid? I am trying to figure out the
> magnification of the 90/2 when combined a 25mm extension tube.
The 90/2 achieves its maximum 1:2 magnification by virtue of its 45mm
focusing helicoid.
Extension/Focal Length = Magnification (M)
45mm / 90mm = 1/2 M
With the 25mm extension tube, we have:
(45 + 25)mm / 90mm = 70/90 = 0.777... maximal M
0 M to more than 3/4 M is an exceedingly useful range. ;-)
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