The move to mirrorless by some of the industry's biggest players put the focus on their new lens lineups.

In our recent look at ~$2000 full frame mirrorless cameras, we said that choosing between them is as much about buying into a lens system as anything else. In this article, we're going to have a look at the four full-frame mirrorless systems to see what they offer and where they might yet go.

This article isn't a question of 'which range is biggest,' it's to help show which lineups have the lenses you might need for your photography.

As well as the lenses currently available, we'll consider the degree of support provided by third-party lens makers and briefly discuss some of the technologies involved.

Sony E-mount

When it comes to full-frame lenses for mirrorless, Sony has the biggest head start. Sony introduced its full-frame 'FE' range alongside the original a7, back in late 2013, and already had several years experience of making APS-C E-mount lenses by that point.

Sony has also taken the unusual move of allowing third-party lens makers access to its lens mount specifications and communication protocol. This has allowed companies such as Sigma, Tamron, Tokina and Zeiss to expand the range of available lenses for Sony photographers. In the case of Sigma, these include existing DSLR optical designs as well as new, dedicated optical formulations for mirrorless.

Diagram covers autofocus primes and high-end zooms in the 14-200mm range. Lineups correct as of April 2020.

In addition to covering most of these bases, Sony has had time to add specialist lenses, such as 600mm F4, 400mm F2.8, 100-400mm and 200-600mm telephoto options, equivalents to which aren't currently available for other systems.

Starting earlier has given Sony time to provide a wider range of lenses, including less obvious options such as the 135mm F1.8 GM

Sony says that the years it's spent making large lenses for mirrorless camera has allowed it to develop expertise in the types of motors best suited for full-frame mirrorless lenses (the need to drive lenses smoothly for video, as well as quickly means the requirements aren't the same as for DSLRs). However, while it's true that Sony's adoption of technologies such as linear motors and piezoelectric drive provides its more recent lenses with impressively fast, smooth focusing, be aware that some of the company's earlier lenses don't always show this same performance.

Canon RF-mount

Canon's RF lens lineup thus far has shown a distinct focus on the needs of professional users, with many of its first lenses belonging to the premium 'L' range.

Canon hasn't opened up its lens mount to other makers, so there's limited third-party support available at the moment. If the RF mount gains anything like the popularity that the EF mount did, it's extremely likely that other companies will find a way to offer autofocus lenses, but widespread third-party support for RF may be some years away.

Diagram covers autofocus primes and high-end zooms in the 14-200mm range. Lineups correct as of April 2020.

Canon currently uses a variety of motors in its RF lenses: primarily using the company's fast, smooth 'Nano USM' technology and the ring-type USM motors that underpin most of its high-end DSLR lenses. These ring-type motors appear to work pretty well with Canon's dual pixel AF system but aren't always the smoothest or fastest, especially given that they tend to be used in the lenses with large, heavy lens elements that need to be moved.

The RF 35mm F1.8, meanwhile, uses a small stepper motor, which makes it noticeably slower and noisier to focus than the best of Canon's other mirrorless lenses.

Nikon Z-mount

Like Canon, Nikon has not yet opened up the Z-mount to third-parties, which currently limits your autofocus choices to Nikon's own lenses.

However, Nikon's initial build-out strategy looks very different from Canon's: Rather than starting with exotica, Nikon has provided a range of comparatively affordable/portable F1.8 primes, alongside a set of F2.8 and F4 zooms.

Diagram covers autofocus primes and high-end zooms in the 14-200mm range. Lineups correct as of April 2020.

In terms of focus motors, Nikon seems to primarily be relying on the use of small stepper motors for its lenses so far, which offer decent performance but don't appear to match linear motors or Canon's Nano USM technologies for either speed or smoothness. Twin focus groups help to give accurate focus even close-up, in some of Nikon's zoom lenses, which can also improve on the often modest speeds of single-motor designs.

L-mount: Panasonic, Leica and Sigma

Panasonic, along with Sigma, has aligned itself with Leica by adopting the 'L' mount for its full-frame mirrorless cameras. This instantly gives it access to an established lens range (though, like Sony's, one that is built around a mount originally focused on APS-C). Sigma's inclusion in the alliance should ensure a wide range of third-party L-mount lenses become available.

All Panasonic cameras so far have been based around the company's Depth-from-Defocus (DFD) AF system. The degree to which lenses from other members of the L-mount alliance are optimized to this system is not clear at this point. We'd expect Leica's lenses, which are designed around a distinctly DFD-like approach to work well but we don't know how closely Sigma has yet embraced the DFD concept. For now we wouldn't expect the same consistency across native L-mount lenses that we've seen from the single-maker systems, but we'd expect Sigma to be working to maximize compatibility.

Diagram covers autofocus primes and high-end zooms in the 14-200mm range. Lineups correct as of April 2020.

Panasonic's lenses primarily make use of linear focus motors, but use a combination of linear and stepping motors for lenses such as the 50mm F1.4 and its 70-200s that require more glass to be moved around.

DSLR lens support

If you already own a selection of DSLR-mount lenses, then you'll find that with the right accessories, you can mount them on any of these camera bodies. Since the mirrorless mounts are all shallower, this leaves plenty of room to put an adapter between the lens and body. The performance you get will vary, though.

Canon frequently bundles one of its EF-to-RF adaptors with its RF-mount cameras, and it makes three variants (a simple pass-through tube, another with a control ring around it and a third that lets you drop a choice of filter between the lens and the camera). The dual pixel AF system, combined with Canon's knowledge of its communication protocol means EF lens users will get probably the best adapted lens experience when using Canon RF-mount bodies. That said, we still wouldn't necessarily expect DSLR-level performance from all EF lenses when adapted.

Unsurprisingly, you tend to get the best adapted performance if you use DSLR lenses on the same brands' mirrorless bodies. Don't expect DSLR levels of performance, though.

Various companies also make EF-to-E adaptors, allowing EF lenses to be used on Sony bodies. And, while not quite as consistent as Canon-on-Canon combinations, we've had good experiences with this combination, though generally only with shorter focal lengths. Meanwhile, Sigma makes the MC-21 adapter for using EF lenses with L-mount bodies but, without phase detection AF in any of those cameras, continuous AF is not available.

Nikon also offers kits that include its 'FTZ' F-to-Z mount adaptor with some of its camera bodies. This provides a decent level of support for existing lenses but does not contain a focus drive motor, so can only autofocus lenses with their own motors (AF-S, AF-P and AF-I lenses and their third-party equivalents). F-to-E adapters are available, but performance can vary, lens-to-lens, making it more of a gamble.

As you'd probably expect, then, older lenses tend to work most reliably with the cameras made by the same brand. However, they can be used on other systems, so depending on how extensive your existing lens collection is, you may find you can make do with lowered performance, rather than having to sell-up and start again, if you don't want to remain bound to the whims of the maker of your DSLR.

Summary

As you'd expect, Sony's nearly five-year head start and openness towards third-party makers has let it build up a significant advantage over its rivals, but all four mounts are already starting to see key holes in their respective lineups being filled.

In the long run, it's likely that all four systems will be extended to offer a range of mid-range, as well as high-end primes and zooms, but it's pretty clear that initially, Nikon and Canon are focusing on different sets of users.

Third-party support provides more options in young lens systems.

Nikon and Canon's decisions to keep their mounts closed to competitors means they can control the consistency of experience for their users (with no risk of a third-party lens offering sub-standard AF speed or smoothness, for instance), but with the downside that you're entirely dependent on that company's development priorities, unless you're happy to take your chances with simple manual focus options.

It's the third-party makers and their ability and willingness to produce fully-compatible lenses that will be interesting to watch. The adoption rate of Sony E-mount cameras and the availability of the lens protocols is likely to mean most future third-party lenses will be designed around this mount but it'll be interesting to see which of the other three systems this support gets extended to.