I didn't measure. The magnification was around 1:3. We can calculate it using the following formula: R = (t-f)/f
where R = magnification ratio, t = bellows extension, f = focal length
Here R = 1/3, f = 210mm, and t is unknown
1/3 = (t-210)/210
1/3 * 210 = t - 210
70 = t - 210
t = 280mm
So I guess I used around 280mm of extension.
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