Stumbled upon this discussion and wanted to share my journey. I went through this last year with my own fp setup. I was highkey paranoid about the electronic connection dropping mid-shoot—literally nothing worse than that "Lens Disconnected" error when you're mid-take. I looked at the Metabones Canon EF to L-Mount T Smart Adapter mentioned earlier, but honestly, the $400 price tag felt steep for my budget. I ended up trying the Viltrox EF-L Mount Adapter which is way more cost-effective at around $130-$150. Technical-wise, it’s been okay with my Canon EF 24-70mm f/2.8L II USM, but i gotta warn you... I noticed a tiny bit of physical play in the mount. It’s kinda scary for safety because if the lens wobbles, those pins might lose contact and kill your recording. I mean, it hasn't failed yet, but you might want to consider how much you're moving the camera. If you're doing aggressive handheld work, just be careful. AF-C is still pretty hit or miss tho... probably just an L-mount thing. gl!

Honestly, I've been there and it's a bit of a headache. Here's what I recommend: - Sigma MC-21 Mount Converter: Super stable for video but unfortunately, AF-C is basically broken.
- Metabones Canon EF to L-Mount T Smart Adapter: Better AF features, but way pricier. If youre on a budget, just grab the MC-21 and manual focus... it's the most reliable for the price. gl!

Seconding the recommendation above! Honestly, i’ve been tinkering with my fp for a bit now and totally get the struggle. If ur looking for a budget-friendly alternative to those pricey ones already mentioned, i’ve been really happy using the Commlite EF-L Electronic Lens Mount Adapter CM-EF-L. It’s way cheaper and basically does the job for video work without those scary connection drops. I’m still kinda a beginner with the technical specs, but i think the main issue is that the original fp uses Contrast Detection AF (CDAF). Basically, the camera hunts for focus because of how the sensor works, not necessarily the adapter pins... so dont blame the gear too much haha! I’ve been using it with my Sigma 24-70mm f/2.8 DG OS HSM Art for Canon EF and honestly, for the price, i have no complaints. It’s stable and feels solid on the body. If ur mostly doing manual focus or locked-off shots for video, this saves u a ton of money. gl! 👍

Yo! Seriously, I feel u on the fp—it’s such a killer little rig but the EF lens situation is a bit of a maze. Since the Sigma MC-21 Mount Converter and Metabones were already brought up, let me drop some technical insights on why they act up and a couple of other options for ur L-series glass: 1. Commlite CM-EF-L Electronic Mount Adapter: This is basically the best value play. It's cheap and surprisingly solid, but honestly, AF-C is still a struggle. 2. Novoflex SL/EOS Adapter: This is the tank—German engineering, zero play in the mount, but it’s pricey and doesn't always support every electronic feature. Technically, the fp uses contrast-detect AF, which is why AF-C feels broken on adapted EF glass. The lens has to "hunt" back and forth, and most adapters just can’t keep up with the data. If stability is your #1 for video work with that Sigma 24-70mm f/2.8 DG OS HSM Art for Canon EF, the MC-21 is still the most reliable choice because it was literally made for it. I mean, just go manual focus for video and save the headache! haha gl! 👍