The 85mm prime is often thought of strictly as a portrait lens, but it also offers a great field of view for walkaround. I came up with a FF film SLR and a wonderful 85mm f/2, which I used as an all purpose lens for years at a time, indoors and out. Digital photography has given me a lot of things my film years didn't give me (primarily garden macro and the EVF shooting experience) but it has never successfully replaced my 85mm walkaround thing. And the older I get, the more I miss it.
So please recommend me an 85mm that is NOT a super fast dedicated portrait lens, and a FF camera to put it on. Can be any system*, DSLR or mirrorless, camera and lens could be old or new-- I am perfectly willing to buy secondhand . I do have a tentative solution in mind, which I will share later. I wonder if anyone will suggest it? I just want to make sure I haven't missed a good option.
*Be aware that Sony is going to be a very hard sell.
So, you're going to choose a camera system based on the 85/1.8 lens available for the system, because you want the 'best' lens. That seems a bit of an odd way to go about things, but it's your money, so you can do as you wish with it.
The point is that 85mm equivalent is undemanding in terms of lens design. Most manufacturers make them, and they are all very good. If you really want 'the best', then the new mirrorless systems have recently computed lenses which will be better than the 85/1.8's available for DSLRs, perhaps with the exception of the Tamron SP 85mm F/1.8 Di VC USD, which was a bit of an outlier in terms of spec for a new lens. If you want a DSLR, that's probably the lens to go for.
Canon has an excellent f/2 macro for the RF system, Nikon a fantastic f/1.8 for the Z system, Sony a very good f/1.8 with independent options available. You wouldn't go wrong with any of these.
In smaller formats, to do the job of the FF f/1.8 (which I presume is what you want) you'll need a 56/1.2 for APS-C and a 42.5/0.9 for mFT. The latter doesn't exist, so can be ruled out. Fujifilm does have a 56/1.2, which is excellent (and expensive). There is also the Sigma 56/1.4 (equivalent to f/2.1 on full frame), cheaper and extremely good.
As to which of these options is 'the best', who knows? What are your parameters for 'the best'? Even at this level of performance each lens has some aspects that are stronger than others. It depends on what you want.
And a final thought. A high resolution body makes a lens perform better than a low resolution one (particularly if it's a good lens), so you really should be thinking about lens/body combinations, not just the lens. If you're going for 'the best', then it comes down to which vendor has a high resolution body to go with its lens. It looks like the Canon R5 with the 85 f/2 macro or the Nikon Z7 (or Mk II) with the 85/1.8, or one of the Sony A7R versions with the one of the available 85/1.8s (probably the Zeiss Batis). Or if you go DSLR it's a matter of what to pair the Tamron with. You could go with a 5DS if you want Canon, or a D800, 810 or 850 for Nikon.
Overall, I would think that the best value 'best' would be a Nikon Z7 (mk I) with the Nikon 85/1.8. The R5 is pricey, as is the Batis, and the Z7 has been superseded by the Mk II so can be had for a good price.
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Is it always wrong
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Comrade Kim Yo Jong?
