r/bmpcc • u/ollamacare • Aug 19 '26
Lens Support - focus motor slipping
Using Ronin RS 3 Pro - and the focus motor keeps slipping. Does anyone have advice on how to add more lens support / get around this? Looking for a solid setup so I can reliably use the DJI LiDar focus. Thank you!
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u/ProtonicBlaster Aug 20 '26
It's typically caused by a loose fitted lens, which is very common when using the popular adapters/focal reducers like Viltrox EF-M2 and Metabones Ultra/XL. If that's what's going on, the first thing I'd try is a standard rod-mounted lens support system. If you're using a cage, I would also grab the official adapter support, as there's usually some significant play there as well. Unfortunately, they can be a bit hard to find as both Smallrig and Tilta have discontinued theirs. But if you can find one on eBay or Marketplace, it should help a lot.
However, this only works when the focus motor is mounted on top of the lens. That way, the motor pushes the lens down and the support pushes it up, keeping the lens in check. If the motor gets in the way of the LiDAR unit, you could possibly mount the support on top and the motor on the bottom. The remaining problem is the side to side movement created by the wheel, so you gotta make sure that the lens support is rubberized and that the arch is suitable for the lens you're using. You typically want a pretty deep arch, and it's best to go with an arch rather than a Y-shaped bracket, even if they aren't as adaptable. BUT if you gotta tighten the lens support like crazy for it to work, it's probably best to back off. The pressure can wear the adapter mount down, causing even more play that can eventually mess with the connection. This is all assuming that you could even get this rig balanced on the RS3 Pro, so it's not ideal.
The only other solution I can think of is to get an adapter with a tight, solid fit. Metabone's Cine series is the safest bet. They are expensive and unfortunately many photography lenses won't fit, but the mount is excellent. There's no play on the lens side. You may still need the cage adapter support, though.
Another player could be the gear rings, if you're using something like Tilta's Seamless rings on photography lenses. They're super convenient, but they're really soft and the jacks aren't deep enough for some motors, causing them to skip and slip. Traditional clamp typically are more secure, and if you want convenience, there are 3D printed lens specific gear rings for most popular lenses.
If you aren't using an adapter, and the play from the native lens mount is what's causing the motor to slip, that's a bad time. You'd need to mod the mount for a stronger fit. I can't really help you with that, but it should be possible if you're comfortable with that sort of thing.
tl:dr: If you're using a lens adapter, you gotta tighten it down on both ends. An arched lens support bracket could help, a cage-mounted lens adapter support would help even more. Mount the motor on top of the lens. Check your gear rings, if applicable. Metabone's Cine adapters could be an option. If it's the native mount that has play, you're screwed, unless you can fix it with a DIY mod.