If you happen to like working with the older Leica gear, one of the very important accessories for macro work, still adaptable to any Leica camera SM, M or R — or indeed any ILC or DSLR — is the Bellows II, 16556 (1961 – 1983). The Bellows II came with a front adapter 16558 to directly take the lens heads of 135mm f/4 Elmar and f/4.5 Hector when combined with adapter OSTRO or 16472. All these older lenses are important ones to consider, as explained shortly.
The Bellows II has an extension of 95mm, primarily designed to reach from infinity to a life-size ratio of 1:1 with a 90mm lens head. It reaches from infinity to greater than 1:1 with the 65mm head, and reaches from infinity to 1:1.5, almost life-size, with a 135 lens head. These ratios are very convenient for close-up and macro work because the bellows provide continuous focus travel without having to exchange extension tubes or front supplementary lenses to get different ratios. And the camera can be rotated from horizontal to vertical by pressing a button on the back panel of the bellows.
The extensions scale on the right side of the rail goes from zero to 95mm On the left side is an exposure factor scale for 90mm lenses only, scaled from zero down to the 4x or two-stop factor for a 1:1 macro image, needed in the days before TTL metering appeared in cameras. For any other lens, the factor can be calculated from the right-side extension scale — such as a one-stop factor for each 34mm of extension with a 135mm lens head of the earlier simple designs such as the Hector or Elmar. (A telephoto design such as the 135mm f/4 Tele-Elmar will require approximately 75% additional exposure due to the telephoto design. However, we can skip all that calculation if we’re using a camera with TTL metering).
On the bottom of the Bellows II is a very important improvement over the earlier Bellows I. It is a micrometer focusing knob which can move the entire bellows and camera unit back and forth over 2 inches on its lower rail for easier and more accurate focus in the macro range, without changing a given extension setting. The knob also has a focus lock for when the rig is mounted vertically, as in a copy setup.
For more extreme macro work great depth of field is needed. At ratios approaching 1:1 and beyond the depth of field is very close to being equal regardless of the focal length of the lens, so a longer length is often preferable to provide more space between the lens and the subject for lighting and manipulation of the subject. According to published table, depth of field at 1:1 is only 2mm at f/16 regardless of focal length!
We also need a lens which has a very small minimum aperture and which stays sharp when stopped way down. There are two Leica lenses we can consider which stop down to f/32 — the 90mm f/4 Elmar and the 135mm f/4.5 Hektor. Those extra-small apertures provided means that these earlier and simpler designs have less diffraction effect at the smallest aperture than more modern lenses which are designed to produce better performance at the largest apertures. More complicated modern lenses will begin to show diffraction after f/11, so their aperture scales are often restricted to f/16. These two earlier designs only begin to show diffraction at one stop short of the minimum, so they still remain sharp at f/22, where the more modern ones should be limited to f/11. That’s two stops of possible added depth available with the older lenses, while avoiding any diffraction at the very smallest apertures. The 65mm f/3.5 Elmar-V goes down to f/22, so is still free of diffraction at f/16.