Why does my 24-105 have a different magnification (macro ratio) from a 105mm macro lens at same MFD?

Monicaa wrote:

I now have both in hand. The panasonic exhibits basically no focus breathing, including at macro ranges, but the sigma exhibits extreme breathing at the macro range. I'm not sure exactly what specifically in your tool would show this,

Sure the Optical Bench shows Pansonic at 105mm is 24 degrees at infinity and 21 degrees at 0.5x whereas the SIgma is 24 degrees at infinity and 9 degrees at 1x.

This makes sense since the Sigma working distance is larger so the angle would be smaller.

but I do think that breathing does seem to play quite a large part, but I am not sure whether as a symptom or a cause.

Neither. It's just different lens designs and the large difference in internodal distance (hiatus) is what results in your original observation.

As a side note, this lens is quite exceptional. I've scanned some film and the detail is quite great, and the corners are just as flawless as the center even wide open, not something I've seen in other macro lenses I've used. I'll need to do some specific testing to see how it performs in 96MP pixel shift high res mode, but from quick tests it appears to still have very high pixel level detail at that resolution. Very impressed.

Both the Panasonic and Sigma exhibit similar distortion according to the Optical Bench; about 3% pincushion. Comparing sharpness requires an actual rather than virtual optical bench !