Fixed-lens outliers aside, most photographers who buy a full-frame camera will end up with an interchangeable-lens model. And before you settle in on a particular camera, you should make sure it's part of a system that meets all of the challenges you face as a photographer. Canon has two full-frame systems available. Its well-established SLR series uses the EF lens mount and offers cameras ranging from entry-level to professional. In 2018, it added the EOS R mirrorless family, which uses the RF mount but can also use EF lenses via an inexpensive adapter. All of Canon's development efforts are now behind RF and we don't expect any more EF lens or camera releases going forward. In addition to its iconic M rangefinder series, Leica launched a mirrorless system in 2015 with the SL camera. It lived in its niche for a few years, but that changed at the 2018 Photokina conference. Leica announced that Panasonic and Sigma were joining it to form the L-Mount Alliance. The trio has put together an interesting mix of cameras. Panasonic has video-tuned options with consumer-friendly prices, Leica makes luxury-priced options, and Sigma covers the quirky side of the market with its fp line. Like Canon, Nikon has two full-frame systems. You can opt for an SLR, which uses the F-mount, and the mirrorless Z-mount system, which launched in 2018. Nikon has been concentrating on making new Z cameras and lenses since the introduction of the line. Its last SLR of note was 2020's D780, and we don't expect to see any more Nikon SLRs going forward. The Z camera line is the future and includes models like the entry-level Z 5, retro Z f, high-resolution Z 7 II, and high-end Z 8 and Z 9. Pentax is an iconic SLR brand but doesn't give owners much choice when it comes to full-frame cameras. It has released two—the K-1 and K-1 Mark II—and the Mark II's upgrades are minimal. Both use a 36MP sensor, include weather protection, and offer in-body stabilization. Sony cameras are all mirrorless these days. Its full-frame and APS-C lines share the same E lens system and work with A-mount lenses from its retired SLR system via an adapter. The mirrorless system is one of the most popular and fully developed. After a decade in the market, the company has delivered models tuned for high-speed action, high-resolution capture, and high-quality video. There are loads of lenses available, both first- and third-party, and Sony continues to sell older models at lower prices, thus broadening the appeal for entry-level buyers.