Let's talk lens adapters
Adapt your EF lenses to other cameras
If you own cameras from multiple brands (or brand-loyalty just isn't your forte), adapting your existing lenses is often the most convenient and cost-effective way to make the switch. You get to keep your existing filters and avoid the expense of having to buy new lenses. But even then, there are big differences in quality and functions between different lens adapters, that can impact your work. Over the years, I've adapted EF lenses to almost every brand, so here are my experiences
Passive vs active adapters
Many of the cheaper lens adapters are passive, meaning there's no communication between the lens and the body. This means: no autofocus, no lens-stabilization, but also no electronic control of the aperture. Because most EF-lenses don't have a manual aperture ring, this means you'll have to set the aperture on a Canon body, before you use the lens with the passive adapter. If you own full manual glass, this won't be an issue, but if your need electronic aperture control, autofocus and/or lens stabilisation, look for an active lens adapter.
But don't expect active lens adapters to be on par with native lens mounts: autofocus performance often takes a big hit, and lens stabilization isn't always supported. Let's take a look at some of the popular adapters for different brands.
EF to Micro Four Thirds (e.g. Panasonic GH5, BMPCC4K)
Because Micro Four Thirds sensors have a 2 times crop compared to full frame, you need a so called 'focal reducer' if you want to adapt your EF glass. A focal reducer is an adapter that contains a glass element which projects the full image circle onto the smaller MFT sensor. Depending on if you use EF or EF-S lenses, you either need a 0.64x or 0.71x focal reducer respectively.
Because focal reducers contain a glass element, you really get what you pay for: the cheaper focal reducers like the Viltrox Speed Booster or the Zhongyi Lens Turbo noticably degrade the sharpness and clarity of the image. The Metabones Speedbooster is a lot more expensive, but is optically far superior to the alternatives. Metabones Speedboosters also support image stabilisation and (single-shot) autofocus.
You can also take advantage of the fact that Micro Four Thirds sensors have a 2x crop: if you buy a regular MFT adapter (without a glass element), you effectively double your lens' reach. That 70-200mm lens now becomes a 140-400mm lens!
EF to L-mount (e.g. Panasonic S5, Sigma fp)
If you want to adapt EF lenses to the L-mount (for full-frame Leica, Sigma and Panasonic cameras), Sigma makes the MC-11 adapter. It allows for aperture-control from the body and supports autofocus, albeit one-shot AF only (no continuous autofocus). Lens-based image stabilization isn’t supported, but luckily all full frame Panasonic bodies have excellent IBIS.
EF to Fuji X (e.g. Fuji X-T4)
The most affordable option for Fuji is the Viltrox FX1, which supports electronic aperture control, image stabilization, and autofocus, but it comes with many caveats. Image stabilization only works for a few seconds after you’ve pressed the shutter button, and although it supports continuous autofocus, performance just isn't consistent. Another option is the Fringer EF-FX adapter, which does support image stabilisation. If your Fuji body has IBIS and you enable the lens stabilisation, IBIS will shut off. Autofocus performance is slightly better than the Viltrox, but continuous autofocus performance is still not reliable enough for video.
EF to RF (e.g. R5/R6) and EF to EF-M (e.g. M50, M6)
You might have noticed the theme by now: continuous autofocus in all these adapters just isn't at a level where it's usable for video. There is one (unsurprising) exception though: the Canon EF to RF and EF to EF-M adapters perform every bit as well as the native mounts. Dual Pixel AF and face-recognition work great, and both lens-stabilization and IBIS can be active at the same time.
When it comes to adapting EF-lenses to other lens mounts, an active adapter has the advantage that you can change the aperture from the camera body and use single shot AF. In my experience continuous autofocus performance just isn't reliable enough for video. If you don't need single-shot AF or stabilization you can also opt for a cheaper passive adapter, but do keep in mind that you can't change the aperture of the lens.