Back in the days of film, for extreme close-ups I used extension tubes, with a reversed Micro-Nikkor 55/2.8. I don't know if the extension tubes were Kenco or not. They worked, but shooting extreme close-ups with film without a sturdy copy stand was not without problems.
More recently, I use a bellows and bellows lenses for moderate close-ups (usually with stacking), and low-power microscope objectives for more extreme close-ups (always with stacking). The finite-corrected microscope objectives are mounted on a bellows. Infinite-corrected objectives are used with a tube lens (no bellows).
More recently, I use a bellows and bellows lenses for moderate close-ups (usually with stacking), and low-power microscope objectives for more extreme close-ups (always with stacking). The finite-corrected microscope objectives are mounted on a bellows. Infinite-corrected objectives are used with a tube lens (no bellows).




















