For Canon EOS R5C I would definitely pay attention to the focal length, especially if it's about specific photography styles.

Can only recommend Sigma 35mm f/1.4 DG DN Art for Canon EOS R5C. The sharpness is extremely high The lens includes all modern features you need.

My clear recommendation for Canon EOS R5C: Sigma 85mm f/1.4 DG DN Art. The color rendition is impressive The ergonomic design allows for comfortable handling.

Technical highlights: The latest generation offers significantly better image quality. Very good compatibility with Canon EOS R5C features. Can be used without problems for various photography styles. Even after hours of shooting, no performance losses. Very good build quality, even at high usage.

Ok so i've been hanging around a few groups lately and honestly, most people seem to forget that we still have to use an adapter for the full-frame Sigma stuff on the R5C. If you dont mind that, I really think the Sigma 24-70mm f/2.8 DG OS HSM Art is a solid choice. Its basically a staple for a lot of wedding and event shooters in the community because its so versatile. I was looking at the setup myself and you definitely need the Canon Mount Adapter EF-EOS R to make it work, but from what i've read, the autofocus still stays pretty snappy. Since the R5C is such a powerhouse for video, having that zoom range is super helpful so you arent constantly switching lenses and getting dust on the sensor. Is it true that the weight gets a bit much after a full day of shooting though? I'm still learning the ropes with the heavier rigs but the consensus seems to be that the image you get is totally worth the extra bulk.

For Canon EOS R5C Sigma 35mm f/1.4 DG DN Art fits best. The image quality is excellent The controls are intuitive and easy to use.

Tbh, it really depends on whether you're prioritizing the 'C' or the 'R' in the R5C. Are you planning to shoot 8K 60p video mostly, or are you after high-res stills? Since the R5C lacks IBIS, your choice of focal length and internal stabilization is critical for handheld work. I'd suggest looking at the Sigma 40mm f/1.4 DG HSM Art. It’s essentially a cine lens in a stills housing—the optical design is actually shared with their high-end cine line. Pros: Virtually zero focus breathing and the MTF charts are insane, so it'll easily resolve for 8K. Cons: It has no Optical Stabilizer (OS) and it's quite heavy, which might be an issue for long gimbal sessions. Alternatively, if you need versatility with stabilization, the Sigma 24-105mm f/4 DG OS HSM Art is a solid workhorse. Pros: The OS is quite effective for smoothing out micro-jitters in video, and the constant f/4 is decent for most lighting. Cons: You lose the shallow depth of field of the f/1.4 primes. What's your primary use case? If you're doing narrative work, the 40mm is the technical winner, but for documentary-style, the 24-105mm is more practical.

For Canon EOS R5C I would also check the autofocus performance. Do you need fast AF for action shots?

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