Simple answer: if you're not a kit-lens-only photographer, five or six.
- Mid-range zoom (minimum 24-70mm equivalent, typically kit, though enthusiasts want something with larger apertures than the kit lens in this range)
- Telephoto zoom (minimum 70-200mm equivalent, typically the kit-lens partner, though enthusiasts want something faster than f/5.6 at the long end)
- Wide, fast prime (24mm equivalent or wider, f/2.8 or faster)
- Normal, fast prime (~50mm equivalent or wider, f/2 or faster)
- Moderate telephoto, fast prime (70-90mm equivalent, f/2 or faster)
- Macro lens (preferably 100mm equivalent or longer)
A kit with those lenses in it would let you make most of the images you'd want. Wildlife, sports, and some event photographers would need more or different lenses, but you'd be surprised how much you can do with just that simple set.
So how do the mirrorless mounts fare?
- Canon EOS M: Only has a fast moderate wide prime, a wide-angle zoom, several mid-range kit lenses, and a telephoto zoom. You can use EF/EF-S lenses via adapter to provide macro and perhaps some telephoto capability.
- Canon EOS RF: You can fill out that kit, but you don't have a lot of options for some of them. Again, you can supplement with the EF lens set on an adapter.
- Fujifilm XF: Has everything on the list, and in some cases, multiple choices.
- Fujifilm GF: Has everything on the list, but often with only one choice.
- Nikon Z: The full frame cameras have everything (or you can use an F-mount macro on the FTZ Adapter). The DX camera (Z50) really only has two kit lens choices; everything else you have to supplement with adapted lenses or dip into third-party lenses.
- m4/3: Has everything on the list, and many in multiple variants.
- Sony (E-mount): By late 2012 Sony was shipping everything on the list, though the macro lens was short in focal length (45mm equivalent). Plus only two of the lenses really start to lived up to the 24mp sensor’s abilities in terms of resolution. Since then, Sony has expanded the lineup to where you can get all of the options, though often with only a single choice. You can also dip into third party lens choices, which are plentiful.
- Sony (FE-mount): The full list now available, from multiple vendors, and with multiple choices.
As might be expected, the "oldest" of the mirrorless systems fare better than the more recent ones.
Beyond the basic lenses, things get more interesting. Technically, a well-rounded system would also have these options:
- Fisheye (180 degree diagonal capability)
- Wide-angle zoom (minimum 18-35mm equivalent)
- Full range of primes (24mm, 28mm, 35mm, 50mm, 85mm, 105mm equivalents)
- Fast mid-range and telephoto zooms (24-70mm, 70-200mm f/2.8 equivalents)
- Long telephoto zoom (300 or 400mm equivalent at long end)
And here's where we are today with that:
- Canon EOS M: the wide angle zoom is available globally.
- Canon EOS RF: some of these are still missing or sub-optimal, though that is changing quickly as Canon rolls out more options.
- Fujifilm (XF): wide angle zoom, fast telephoto zoom, and additional primes appeared in 2014/2015/2016. Fujifilm is still really lacking the long telephoto lenses.
- Fujifilm (GF): Missing a number of these lenses, and not likely to get some (the long telephotos).
- Nikon Z: missing the fisheye, but everything else is basically available.
- m4/3: has options in all of the categories; now adding lots of overlapping and specialty options
- Sony (E-mount): future roadmap unknown, but now has serious third-party lens support that can fill out the needs.
- Sony (FE-mount): current lenses have everything on the list, though the fisheye will have to come from someone other than Sony.
The net takeaway, at least here in 2022, is that m4/3 was the first to a complete set of lens options (and with many multiple choices), and was actually already there in 2012. Sony would arguably come close to the basic set I outline for the crop sensor models, but still has some quality issues in a few of the offerings. Sony's full frame lineup is basically near complete. Fujifilm is still a bit in catch-up mode at the telephoto end, but they're basically there with everything else. Canon is a laggard in the M mount, with only a few lenses available and only two known to be in development. Canon's RF mount is developing rapidly and filling all the gaps. Likewise, Nikon Z mount (FX) is developing rapidly and has pretty much already filled all but the fisheye gap.
Of course lens size and lens quality and other factors come into play when deciding between systems. But just based upon availability, m4/3 is the clear leader in terms of serving their users' basic needs, and even manages to serve extended needs well.
Note: Obviously I love choice, as do most photographers. I'm not arguing that companies should only do the lenses in the two lists, above. I'm only suggesting that those are two good starting points to evaluate whether a system offers reasonable choice. One would hope that we eventually get to the level of the DSLR systems, where 30 or more lenses are available for a mount at any given time, and the used market increases those options as lenses come and go.
