I switched after nearly 50 years with Nikon. I decided to do mirrorless and have a very severe and rather esoteric visual handicap. Was having great troubles with the Z7 AF although my D500 has been a stalwart. I switched to the Canon R5 and it took care of my AF problem and is an incredible camera. Just used it on an expedition to Iceland with wonderful results. I found the transition easy and love the R5 feature where you can switch from full frame to APS-C in the body. The 100-500 telephoto zoom lens is also unbelievable. with the APS-C mode you are getting 800MM and with the combined body/lens stabilization Canon claims you get up to seven stops. Users have reported more likely about 5 but this is still huge, reducing the need for a tripod. I, for one, say go for it. I did and have been very happy. Love the 45MP for my RAW shots too.

I had very good luck on Kodiak Island during the salmon run and never felt threatened in any way, getting some very nice shots with a Nikon D500 and an equivalent 450MM lens at f/5.6 max. For variety, another great AK bear trip is to Kaktovik on the Beaufort Sea near the Canadian border. There is a migration of Polar Bear that comes in there. The tour I took used a bush plane from Fairbanks to get us there. Two or three days is plenty.

Looks as if you are getting the proverbial Heinz 57 varieties answers so might as well add another. I have been to Africa game parks five times, spanning from Namibia to Kenya. They are great. If you have the flexibility, I would most of all, try to stay at reserves near the National Parks. Many of the National Parks will not let your vehicle off the established roads. in the private adjacent parks they can go anywhere on the reserve. I have seen a South African guide near Kruger find animals within 500 yards of a trail that could not even begin to be detected from the trail. That said, given my experience, I have always been in or very near my vehicle so equipment weight is not a big thing in my experience. Therefore, I would take the two Nikons and the two Nikon lenses. Most likely, you will use the 70-200 the most on the 850 body. But as you can see from all the answers, there is no one great formula.

I have tried some of the alternate brands, including Watson. Maybe just bad luck but lifetime of the alternative brands has consistently been shorter than the Nikon batteries. Cost per hour of useful life seems to be about the same, but I prefer the longer lifetimes.

You are getting good advice from the other replies, but you have to be lucky to get much from the bus tour--would follow suggestion of 100-400 for sure with the bus. Depending on the cruise line and your budget, some do have vans or even private cars for the tour. You get some fantastic photo opps if that is available and affordable. Another angle is forego the cruise bus tour and get yourself a rental vehicle and necessary admissions to do it yourself as the camper advisee suggested. In any case, good luck--have done AK eight times--all good!

I use windows and am satisfied. You do need adequate RAM and storage, but I enjoy having a BenQ Monitor which is photo quality.

I have the R5 and the above advice to you is "spot on" to my experience. I would add that I bought the 24-240 instead of the 105 that is pushed in the kit. With the crop factor available this gives you up to 384 mm capability in a very lightweight package.

Assuming the lenses perform equally, for one stop I would increase the ISO. The other advice to get a longer lens is really useful for Yellowstone. If you are lucky enough to see the wolves long enough for photos, you will need that! Good luck!

I have the Nikon 60mm and the Sigma 105, and for my purposes, both are excellent, but admittedly, I have not put either of them into stressful environs. The Nikon 60 is built a little better to me but as several have pointed out, you get more flexibility with the 105. I think you will be happy with either. The Sigma I have will not work with the Z line adapter autofocus so becomes a manual focus which in many macro situations is what you might do anyway.

An important addendum. B&H, for one, has a PayBoo card that rebates sales tax which can represent a couple of hundred savings on a large purchase. Easy to get and B&H does no even push it for any use than helping on sales tax issues.

Interesting suggestions from all. I have done all continents and more than 125 countries ( entities) Would say Yellowstone in winter, polar bears on Arctic ice in NE AK, Galapagos, and a compendium of some of the classic sights/ monuments of Europe, for my own tastes.

I concur with the BenQ suggestion and also raising your budget a bit. I think you will be glad you did.

I have had a D500 for several years and think it is great. Would not trade it at this time as already noted by others. The Mirrorless offer limited advantages. I have a Z7 which is partially GAS. One little advertised thing about the Z7 is that it is not only full frame but will readily use DX lenses, all with the FTZ adapter. It does offer two things I like that are not on the D500: Focus Stacking and a very good full EVF that is plenty bright. While Sony does get rave reviews, the new Canon R5 has impressive specs and very economical lenses. Both the Canon and Nikon can use teleconverters very effectively on zooms at F stops that far exceed the D500.

Many of the people doing focus stacking are using such bodies as the Nikon Z7 and 850 which will do up to 300 images stacked which with one of the several stacking programs yield excellent results with minimal hassle. On the other side, take a look at Mike Moats who has a Macro Photo Club online and is a strong advocate for small aperture such as you suggest. His gallery has some pretty surprising results shot at f/22 and greater. I lean toward the stacking, but both have a lot of pros and cons, especially if you do not have a camera with the auto-stacking feature.

I have the Z7 and as noted, the adapter works seamlessly with regular size lenses although I have an older 80-400 AF-VR which will not autofocus but does fine on other auto features. I like having 45MP for cropping and the lighter weight. It has, with my poor sight, the first EVF that I can actually use in bright light, and as you know, it covers 100%. I let the XQD card handle the RAW and the SD handle the jpg which is a feature I like. With the later version II you get even more flexibility--Z series much lighter than the 850 with many specs the same.