[Brightcolours]

       ....... not to be confused with the G1!!


https://www.tamron.eu/lenses/sp-150-600m...vc-usd-g2/

1:39X is still not a thing, no matter if you write G1 or G2. Both do 0.26x, by the way.

  What do you mean by a thing exactly  ??

It is either something is either a ratio (1:2 for instance) or a magnification (times something), like 0.5X. So not 1:39X. And 1:39 would be 0.0256x max. magnification, which does not seem right either. 

   I'm now confused too about maths .... but which ever way you roll the dice  a ratio of "1:0.14" is pretty poor on the magnification scale of things ......

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Tamron G2 MFD max mag 1:0.39 ..... magnification equals 0.39 squared = 0.1521X     ...... maybe 

Hehee...

No.

Tamron 150-500mm magnification: 1:3.9.  So about 1:4. Meaning: 4 times the film/sensor width is the minimum with the subject can have to be frame filling. That is about 0.25x max. magnification.
Calculate one from the other notation:
1:3.9 -> 1 / 3.9 = 0.2564x
Or if you have 0.25x -> 1 / 0.25 = 4 -> 1:4 ratio

Both the G1 and G2 have the same max. magnification.