Magnification with Tamron 28-75mm lens on Sony camera

[rpcrowe]

The 28-75mm f/2.8 Tamron lens for my Sony mirrorless cameras has a pretty decent close-up capability of from .25:1 at 28mm to .34:1 at 75mm. However, I also have a set of two extension tubes: 10mm and 16mm which could add up to 26mm. I wondered what kind of magnification I could achieve from this lens using the extension tubes.

Here are the magnifications for the Tamron at 28mm
10mm .65x magnification
16mm .82x magnification
26mm 1.18 magnification

For the lens at 75mm
10mm .47x magnification
16mm .55x magnification
26mm .69x magnification

I also have a set of close-up filters/diopter lenses (I received these with a lens that I purchased used on eBay)
For the lens at 28mm
+1 diopter .29x magnification
+2 diopter . 32x magnification
+4 diopter .39x magnification
+10 diopter .60x magnification

For the lens at 75mm
+1 diopter .44x magnification
+2 diopter . 54x magnification
+4 diopter .74x magnification
+10 diopter 1.35x magnification

Reference for above: https://www.cambridgeincolour.com/tu...es-closeup.htm

I haven't used either the extension tubes or the diopter lenses because the bare close-up capabilities of the Tamron lens are usually enough for my uses and I have a 60mm macro lens which will provide a 2:1 image ratio without any added tubes or diopter lenses. However - my calculations from the above table indicate that with this lens I could achieve a maximum 2.43x to 1 image ratio with 26mm of extension tubes and if I had a 62mm diopter filter, I could achieve a 3.8x to 1 image ratio.

I am wondering if I used a 62mm to 67mm step-up ring on the macro lens with a 67mm diopter filter; would this change the effective diopter of the filter since I would only be using the center portion of the filter and because the filter would be slightly further away from the front element because of the adapter ring...

[DanK]

However - my calculations from the above table indicate that with this lens I could achieve a maximum 2.43x to 1 image ratio with 26mm of extension tubes and if I had a 62mm diopter filter, I could achieve a 3.8x to 1 image ratio.

I no longer recall any of the technical details, but my recollection is that the standard formula for magnification with tubes doesn't work with macro lenses at close to MWD. However, you can sort this out easily. Focus on a ruler at MWD. This should give you 36 mm horizontally in the frame (1:1). Then redo it with various lengths of tubes. I did this years ago, and my recollection was that a full set of kenko tubes gave me very roughly 2:1 with my 100mm macro, which is effectively 70mm at MWD.