I am a Nikon shooter from way back in Nikonos days. have gone through many Nikon DSLRs and housed D200 and D300 with aquatica housings and Ike 125's then 160s. Had a long hiatus as my veterinary practice grew too fast. Now I find myself wanting back in the water at 72 but still capable with my favorite DSLR ever the D850. I could make the jump to mirrorless but the D850 is so much more capable than anything I've used I say why not make my underwater last run with my favorite camera? Just need a used housing , I have all the rest. Or does it make sense to jump to mirrorless for the focus improvement. new housing and new camera. but also new lenses. would appreciate some opinions and wisdom. Thanks. Wally

Honestly from what I've read the D850 can do still images with all but the newest mirrorless.

Plus I'm betting you can find a housing for a decent price if you keep your eyes open.

Many people are still using adapted lenses from that era.

The quality and focus abilities of the D850 are at least 90% as good as anything else on the market. Certainly the lenses are as well, often its the same lenses. There are clearly advantages to mirrorless models, which is why i upgraded to the Z8. However, i kept my D850 and housing as a backup. You would be very happy with that system and can get years of use out of it.

Is there anything you can’t do with your D850 that you think you might be able to do with, say, a Nikon Z? I doubt that focussing or underwater image quality will be significantly better with mirrorless.

I’ve been a long-time D500 user (and like you D100, 200, 300 and 800) and hankered about going mirrorless. But the only real advantage I could think of was in-viewfinder review. A very nice feature, especially for macro, but at huge cost: new body, new housing.

As Dave suggests, you can probably pick up a used D850 housing in great condition for an excellent price. Two have been advertised recently on our Marketplace.