Chan, last year I broke down and bought a used D810 to use with my MF Micro-Nikkors for closeup work, including fish in aquaria. I'd never handled a D810, had played with a D800. The two have about the same viewfinder, the D800 convinced me that a D810 would do. Besides, at the time used Nikon Z cameras all cost more and I couldn't find one locally to play with.
This was a bit of a mistake. My fish room is relatively dark. The D810 can be focused manually on fish in a well-lit aquarium by teetering in and out but focusing is much too hard with fish in my little portable photo tank, which isn't lit at all. I'd have been happier with a camera with an EVF. Or so I thought.
Since I didn't want to eat the D810's depreciation and shell out for a used Z, I bought a used 105 AF MicroNikkor.
Big problem solved, another smaller problem found. I used Vivitar 283s with VP1s for lighting. All calibrated, just pick the aperture needed given magnification. A handy table is taped to the 283s. Want to change aperture, futz with the VP1s, not fun. Fine, but the AF lens focuses by changing magnification, not by changing working distance. Solution? A couple of Nikon SB-600s with the necessary cables. Works a treat, and inexpensive.
I still wish I'd had the money to buy a Z but what I have will do.