I'm looking at 3 different lens mainly for distance shots but with a bit of Macro occasionally.

Tamron AF 70-300mm F/4-5.6
Nikon AF-S DX NIKKOR 55-300mm f/4.5-5.6G
Sigma 70-300mm f4-5.6

The bit I'm confused about is the optical zoom. I thought if they all had the same Max Focal Length that they'd have the same optical zoom. However what the spec's say is that the Tamron is 2x, the Nikon 5.5x and the Sigma 4.28.

Can someone explain why the optical zoom is so different?


Edit: Spec's got from here: Amazon comparison about half way down the page


2 Answers 2


All three zoom out to 300mm i.e. that is the maximum magnification. The 70 – 300 has a zoom range, the minimum vs. maximum is 300 ÷ 70 = 4.28. The 55 – 300 has a zoom range of 300 ÷ 55 = 5.5. The 70 – 300 has a zoom range of 300 ÷ 70 = 4.28. The difference is the span of the zoom from minimum to maximum. All three have the same maximum zoom but the minimum magnification is different. Two have a minimum focal length of 70mmm, one has a minimum focal length of 55mm.


There's a difference between "zoom" and "focal length". Not sure where you got your data from though, because that Tamron and Sigma have the same zooming capability (4.28x zoom).

  • I think it was the odd Tamron spec that must have confused me. Thanks
    – AidanO
    Nov 23, 2017 at 17:26

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