When you switch camera bodies, you don't have to leave your lenses behind. A mount adapter bridges the gap between your existing glass and a new camera system. The two adapters here solve very different problems: one connects Canon EF/EF-S lenses to Canon EOS R bodies, and the other connects B4 2/3-inch lenses to Sony E-mount cameras. Both are new, both are listed as lens adapters, but they serve different shooters. Which one makes sense for you? Let's compare the Canon Mount Adapter EF-EOS R at $129.95 and the Lens Mount Adapter Ring B4-NEX at $58.99.
Quick Verdict
If you own Canon EF or EF-S lenses and want to use them on an EOS R mirrorless camera, the Canon Mount Adapter EF-EOS R is the straightforward choice. It's a Canon-branded adapter with a listed price of $129.95. If you work with broadcast-style B4 2/3-inch lenses and shoot with a Sony NEX or E-mount camera, the B4-NEX adapter from the listing at $58.99 gives you a lower-priced way to mount that glass. In short: the right adapter depends on the lens and camera combination you already have.
Comparison at a Glance
| Product | Listed Price | Lens Fitting | Type | Price Indicator |
|---|---|---|---|---|
| Canon Mount Adapter EF-EOS R | USD 129.95 | Canon EF | Lens Adapters | |
| Lens Mount Adapter Ring B4-NEX | USD 58.99 | for B4 2/3\" lens | Lens Adapters |
The price spread between the two is about $70.96, with the Canon adapter at the higher listed price and the B4-NEX adapter at the lower listed price.
Where Each Adapter Wins
Canon Mount Adapter EF-EOS R: This adapter wins for Canon shooters moving to EOS R. It's listed as brand Canon, new, and it's designed specifically for Canon EF/EF-S lenses to fit EOS R cameras. The lens fitting is Canon EF, so it's a direct native match for that lens family. If you're already invested in EF or EF-S glass, this is the listed option that matches your system.
Lens Mount Adapter Ring B4-NEX: This adapter wins for Sony E-mount users who want to use B4 2/3-inch lenses. The listing says it's made for B4 2/3-inch lenses and fits a wide range of Sony NEX and E-mount cameras, including models like the Sony A6300, A7, A7R, A7II, A7S, NEX-7, and NEX-6. It's also the lower-priced option at $58.99. If your lens collection is B4 glass and your camera is Sony E-mount, this adapter is the budget-oriented path listed here.
Product Notes
Canon Mount Adapter EF-EOS R for Canon EF/EF-S Lens to EOS R Camera
The Canon Mount Adapter EF-EOS R carries the Canon brand and is listed as new. It's designed to let Canon EF and EF-S lenses work on EOS R cameras, with a lens fitting of Canon EF. The listed price is $129.95, making it the higher-priced adapter in this comparison. For photographers who own Canon EF or EF-S lenses and are moving to an EOS R body, this adapter is the direct, system-matched option. The main limitation is that it only addresses Canon EF/EF-S to EOS R compatibility; it won't help if you're trying to mount B4 or Sony-mount lenses. If your camera and lens are Canon EF/EF-S to EOS R, this is the listed solution that matches your gear.
Lens Mount Adapter Ring B4-NEX for B4 Lens to Sony NEX E-mount Camera
The Lens Mount Adapter Ring B4-NEX is listed at $58.99. It's designed to mount B4 2/3-inch lenses onto Sony E-mount cameras, including popular NEX and alpha models like the NEX-7, NEX-6, A6300, A7, A7R, A7II, and A7S. Its description notes that it's made of brass and aluminum, with a black finish, and that diaphragm control is set manually. This makes it a compact, lower-priced bridge for B4 broadcast-style lenses. Keep in mind that manual diaphragm control means you'll adjust the aperture by hand. The adapter is specifically for B4 to Sony E-mount, so it won't cover Canon EF or other lens mounts. If you're using B4 glass on a Sony E-mount body, this is the matching lower-priced adapter.
Final Choice by Use Case
- Choose the Canon Mount Adapter EF-EOS R if you use Canon EF or EF-S lenses on an EOS R camera and want a Canon-branded adapter. The listed price is $129.95.
- Choose the Lens Mount Adapter Ring B4-NEX if you use B4 2/3-inch lenses on a Sony NEX or E-mount camera and want a lower-priced adapter at $58.99. Be ready for manual diaphragm control.
Both adapters solve a real compatibility puzzle, just for different systems. Match the adapter to the lens and camera you already own, and you'll get the most from your gear.
