I don't seem to be able to find the technical data - magnification, working distances of the 120mm TS lens with the Phase One Auto Extension Rings. Can anyone point me to the right direction? Appreciate any help. Thanks.
I have the lens and the auto extension rings.
The minimum focus distance is 84cm
Maxium Magnification ratio is 0.16x
To calculate working distance and magnification with any lens, you just need the basic math for magnification vs extension shown in this article*
Macro Extreme (technicals) | Doug Peterson. Using that math you can back out the amount of extension the lens natively allows, add the extension you want to add in the form of tubes, and recalcule the resulting magnification.
So since the 120mm TS reaches 0.16x magnification
Magnification = [Extension – Focal Length] / [Focal Length]
0.16 = [ext - 120] / [120]
120*0.16 = [ext - 120]
19.2 + 120 = ext
139.2 = ext
So the 120 TS provides 139.2mm max extension natively.
If you then add 36mm (the largest tube, solo) then...
mag = [139.2 + 36 - 120] / [120]
mag = [55.2] / [120]
mag = 0.46
Or very roughly 1:2 magnification rather than roughly 1:6 magnification you get natively.
You can repeat the above for other combinations of extension tubes. The math also works for any brand/make/model of lens/tubes. Just remember that being able to focus a given lens to a given magnification does NOT guarantee that lens will perform well at that magnification; in your specific case that lens will perform well at more than it's native maximum. Though the closer you get to 1:1 the more I'd suggest switching to a 105HR on a tech camera like an Actus or Universalis.
Remember that Phase One is not a SKU on some website, it's a product distributed by knowledgable partners who can help you with questions like this one. Don't be afraid to put your dealer to work; it's literally their job to help!