Choosing a lens mount adapter usually comes down to one question: which lens do you want to put on which camera body. The four adapters in this guide each solve a different pairing, so the right choice depends on the camera you own and how much electronic communication you need. Before you buy, identify both ends of the connection: the lens mount you are starting with and the camera mount you are going to.
Quick take
If you are moving Canon EF or EF-S lenses to an EOS R or RF mount body, the EF-EOS R adapter is the matching choice because it is the only one here that keeps autofocus, image stabilization, EXIF, and electronic aperture control. If you have M42 manual lenses and a Canon EOS body, the M42-EOS ring offers the lowest listed price in the set. If you own 2/3" B4 lenses and a Sony E-mount camera, the B4-NEX adapter is the dedicated bridge. If your body is a Leica or Panasonic L-mount camera and your lenses are M42, the K&F CONCEPT M42-L adapter is the metal ring to pair.
Listed price comparison
| Adapter | Listed price | Price bar |
| B4-NEX for Sony E-mount | USD 58.99 | |
| K&F CONCEPT M42-L for L-Mount | USD 29.99 | |
| M42-EOS for Canon EOS | USD 6.67 | |
| EF-EOS R for Canon RF Mount | USD 28.49 | |
Decision matrix
| Use case | Adapter | Why this match |
| Canon EF or EF-S lens on Canon EOS R/RF body | EF-EOS R | Retains autofocus, IS, EXIF, and electronic aperture control |
| M42 manual lens on Canon EOS body | M42-EOS | AF-confirm chip; supports AV and Manual modes |
| M42 manual lens on Leica or Panasonic L-mount body | K&F CONCEPT M42-L | Matching L-mount adapter for M42 lenses; manual operation |
| 2/3" B4 lens on Sony E-mount body | B4-NEX | Purpose-built for B4 to Sony E-mount; manual diaphragm control |
Product notes
#### Lens Mount Adapter Ring B4-NEX for B4 Lens to Sony NEX E-mount Camera
This is the adapter to consider when you own a 2/3" B4 mount lens and want to use it on a Sony E-mount body. The compatibility list includes a long lineup of Sony NEX cameras, Alpha models such as the A6300, and several E-mount camcorders. The ring is made from brass and aluminum and is finished in black. One reason to choose it is the dedicated B4-to-E-mount pairing. The limitation is that diaphragm control is set manually, so aperture adjustment is a hands-on step. If your B4 lens works best with manual control, this adapter fits that workflow.
#### K&F CONCEPT Lens Mount Adapter M42-L Manual Focus For M42 Lens to L Mount Camera
If your camera is a Leica L-mount body or a Panasonic Lumix S model, this adapter is the one that brings M42 manual lenses into that system. Compatible bodies include Leica SL, SL2, T, TL, TL2, CL and Panasonic Lumix S5, S1, S1R. The ring is made from brass and aluminum and is designed for manual operation with infinity focus allowed. The strength is a direct L-mount connection for M42 lenses. The trade-off is that this is a manual adapter, so aperture and focus are controlled by hand.
#### Lens Adapter Ring M42-EOS For M42 Mount Manual Lens to Canon EOS Camera
For the lowest listed price in this set, this ring attaches M42 screw-mount manual lenses to Canon EOS cameras. A third-generation AF-confirm chip can give a focus confirmation signal, and exposure aperture data can be recorded in EXIF. It supports aperture-priority AV mode and manual mode, and it allows infinity focus when you focus manually. The practical limitation is that this is a manual-adapter path: you set aperture and focus on the lens, then use the body's confirmation cues to judge focus.
#### EF-EOS R Len Mount Adapter Accessory For Canon EF EF-S Lens To EOS R RF Mount
This is the RF-mount bridge for Canon EF and EF-S lenses. It supports autofocus, image stabilization, EXIF information transmission, and electronic aperture control, all through gold-plated contacts. The body is aluminum alloy and uses snap-on fastening with snap clips. If you are moving from a Canon EF DSLR to an EOS R-series mirrorless camera, this adapter is the one that preserves the electronic functions you are used to. The trade-off is that it is built for a single pairing: Canon EF/EF-S lenses to EOS R RF mount, rather than a universal ring.
Final recommendation by use case
- For Canon EOS R or RF body with EF or EF-S lenses, choose the EF-EOS R Len Mount Adapter.
- For Canon EOS body with M42 manual lenses, pick the Lens Adapter Ring M42-EOS.
- For Leica or Panasonic L-mount body with M42 lenses, go with the K&F CONCEPT M42-L.
- For Sony E-mount body with a 2/3" B4 lens, go with the Lens Mount Adapter Ring B4-NEX.
