I found a Marumi Achromat close-up lens in 58mm Ø which i could easily adapt to the Contax Carl Zeiss 100 mm ƒ3.5 lens, which allowed me to get closer. I just wanted to test that, since it had it at home (actually i found it again).

It worked pretty well !

It poses a good option

if you wish to reduce the minimum focus distance, getting closer (given that the Car Zeiss 100mm lens normally only goes down to 1 meter - which is not very close). So, yes the Marumi Achromat works really very well on 3D motives in particularly. Also; the lens still does not vignette on a Fujifilm GFX camera - even with a lens hood attached.

Really remarkable !

Naturally, at wide open aperture, the DOF (depth of sharpness) is extremely thin, while sharpness softer (but still useful. Stop the lens down, and you get good sharpness with definition. Using achromat close-up lenses is an affordable way to extend a lens' usefulness. It isn't meant as a replacement for true macro lenses, nor meant for flat objects like books, film negatives, stamps etc.

Cheap China close-up sets ? Nah !

Some cheap china close-up lens sets for cheap prices.. ain't worth the name. The results are horrible with fringing / chromatic aberrations and vast blurry borders. Unless you need blurry impressions - which can actually work for certain motives. But as soon you wish definition in finer details, these China close-up lens sets, are not recommended.