Confused about focal length and Magnification - Help Please

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MrFlash2 New Member • Posts: 1
Confused about focal length and Magnification - Help Please

My Sigma 150mm 2.8 macro lens has a minimum focus distance of 15" (380mm) and a magnification factor of 1.0x or 1:1 - life size

My Tamron 35-150mm 2.8-4 has a minimum focus distance of 17.7" (450mm) and at 150mm has a magnification factor of 0.27 or just over 1/4 life size.

How can the 150mm Sigma at 15" and produce 1:1 but the 150mm Tamron at 17.7" only produces 1:3 ???

The focal lengths are the same, the focusing distance is pretty close, but the magnification is dramatically different. Makes no sense to me. Can someone explain?

Thanks

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