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By Ked · June 2026

Leica Lens Mounts Explained: Why eBay Gets L-Mount vs LTM So Wrong

June 2026

Search "Leica L-mount" on eBay and you will see, mixed in among modern Leica SL lenses, a number of pre-WWII screw-mount Elmars from 1935. That's not a Leica problem; it's a categorization problem. The phrase "L-mount" has been used at different times for two completely unrelated systems separated by 89 years: the original 39mm Leica Thread Mount (1925, also called LTM or L39) and the modern bayonet L-mount (2014, used by current Leica SL bodies and shared with Sigma and Panasonic under the L-Mount Alliance). A buyer who doesn't know the difference can wire $5,000 for a Summilux-SL when they meant to buy a $400 Elmar, or vice versa.

This post walks every Leica lens mount system made over the past century and lists which bodies use each one. It ends with the eBay miscategorization problem and how to identify what you're actually looking at from a seller's photo.

LTM / L39 / M39: The Original Leica Thread Mount (1930–1960)

The original Leica I (Model A, 1925) shipped with a fixed Anastigmat lens and no interchangeable mount. The interchangeable 39mm screw mount debuted in 1930 with the Leica I Model C (the "Schraubgewinde," meaning "screw thread"). The lens uses a 39mm-diameter male thread on the rear that screws into a matching female thread in the body. The flange focal distance (the distance from the mount face to the film plane) is 28.8mm. The thread pitch and the FFD became the Leica Thread Mount standard, abbreviated LTM, L39, or M39 in various sources.

Bodies that use LTM:

• Leica II (1932) through IIIg (1960). Every screw-mount body Leica made.
• I family with interchangeable lenses (Ic, If, Ig). Same mount as the II/III line.
• Leica Standard. Same mount.
• Many non-Leica bodies: Canon's screw-mount rangefinders (1939–1961), Nicca, Reid, Leotax, FED, Zorki, and most other rangefinder cameras of the 1930s–1960s used the same 39mm thread.

LTM lenses can be used on M-mount bodies via an LTM-to-M adapter ring. The adapter is cheap, ubiquitous, and the M body's rangefinder cam follower reads the LTM lens correctly through it. This is how a 1935 Elmar 50mm f/3.5 can shoot on a 2026 M11.

M-mount: The Bayonet Standard (1954–present)

Leica introduced the M3 in 1954 with a new four-flange bayonet mount. The 39mm screw thread was dropped in favor of a quick-mount bayonet with a 44mm bayonet diameter and a 27.8mm flange focal distance. The M-mount has been Leica's flagship lens mount ever since.

Bodies that use M-mount:

• Every Leica M from the M3 (1954) to the M11 (2022–present). Mechanical film, electronic film (M7), and every digital M (M8, M9, M240, M10, M11) all share the same mount.
• Leica CL (1973), Leitz Minolta CL (1973), Minolta CLE (1981). Same mount.
• M-mount third-party bodies: Voigtländer Bessa R2M / R3M / R4M (film), Zeiss Ikon ZM (film), Konica Hexar RF (film), Epson R-D1 (digital), Rollei 35 RF (film), Pixii (digital).

The M-mount is what most people mean when they say "Leica lens." Modern M-mount Summicrons, Summiluxes, APO-Summicrons, and Noctiluxes all use this mount and work on every body listed above.

R-mount: The SLR Mount (1964–2009)

Leica's reflex (SLR) system uses a different bayonet with a 47mm flange focal distance, deeper than the M-mount because an SLR mirror needs room to swing. The R-mount was introduced with the Leicaflex in 1964 and ran through the R9; Leica formally announced discontinuation of the R-system on 4 March 2009.

Bodies that use R-mount:

• Leicaflex, Leicaflex SL, Leicaflex SL2.
• R3, R4, R4s, R5, R-E, R6, R6.2, R7, R8, R9.
• Digital Module R (DMR). A digital back that attached to an R8 or R9 body.

R-mount lenses can be adapted to M bodies. Novoflex and Leitax make R-to-M adapters with the ~19mm spacer needed to bring the R lens out to its proper 47mm flange distance. The catch is that R lenses have no rangefinder cam, so focusing is by Live View on a digital M (M Typ 240, M10, M11) or by scale focus and guesswork on a film M. The setup is much more pleasant with Leica's hot-shoe EVF accessory: the EVF2 (Olympus VF-2 rebadge, for the M Typ 240), the Visoflex Typ 020 (for the M10 generation), or the Visoflex 2 (for the M11, backward-compatible with the M10 via firmware). It gives you eye-level electronic viewing with focus peaking and magnification instead of squinting at the rear LCD. With an EVF mounted, an adapted R lens on a digital M is a genuinely usable combination. On a pure film M without a coupled rangefinder for the R lens it's a clumsy setup. R lenses also adapt cleanly to L-mount and to other mirrorless mounts (Sony E, Fuji X, Micro Four Thirds). Adapted-R on modern mirrorless is one of the more interesting corners of the used market: the R-mount lens lineup is genuinely excellent and the bodies are cheap, which makes adapted-R a viable Leica entry path.

R-mount has its own complexity: the bodies evolved through multiple metering-coupling schemes (1-cam, 2-cam, 3-cam, R-cam, ROM), and a given R lens may or may not work on a given R body depending on which cams it has. That's a separate post.

S-mount: The Medium-Format-Style Mount (2008–present)

The S system uses a 30×45mm sensor (Leica calls it "ProFormat," larger than 35mm full frame but smaller than true medium format). The S-mount bayonet is unique to this system; S lenses don't mount on anything else, and nothing else mounts on S bodies.

Bodies that use S-mount:

• Leica S2 (announced 2008, shipped 2009), S (Typ 006) (2012), S-E (Typ 006) (2014), S (Typ 007) (2015), S3 (2020).

The S-mount lens lineup is small, about a dozen primes plus a handful of zooms, and all are very expensive. Used examples typically run $4,000–$8,000+. There's no real "Leica lens mounts explained" reason to talk about S-mount beyond noting that it exists; the system is a commercial-pro niche and the mount is closed.

L-mount: The Modern Mirrorless Standard (2014–present)

This is where the eBay confusion comes in. The L-mount is a bayonet with a 51.6mm inner diameter and a 20mm flange focal distance, a short FFD that's typical for mirrorless designs (no mirror box, sensor close to the mount). Leica introduced it in 2014 with the original Leica T (Typ 701), an APS-C body. The mount was originally called the "T mount" but was renamed L-mount in 2015 when Leica launched the full-frame SL (Typ 601).

Bodies that use L-mount:

• Leica T (Typ 701), TL, TL2. APS-C mirrorless. Originally branded "T mount"; physically the same L-mount.
• Leica CL (2017), a completely different camera from the 1973 rangefinder CL. APS-C mirrorless, L-mount.
• Leica SL, SL2, SL2-S, SL3, SL3-S. Full-frame mirrorless.

In September 2018, Leica announced the L-Mount Alliance with Panasonic and Sigma, opening the mount to third-party lens and body manufacturers. The Alliance has since added DJI (2022) and Blackmagic (2023). Today the L-mount ecosystem includes:

• Leica's full SL line
• Sigma fp, fp L (full-frame mirrorless bodies)
• Panasonic Lumix S1, S1R, S1H, S5, S5II, S5IIx, S9, plus various follow-on bodies
• Dozens of L-mount lenses from Leica, Sigma, and Panasonic, many at price points well below Leica's own pricing

L-mount Leica lenses are universally modern: bayonet mount with electrical contacts, often heavy with electronic-focusing elements, optical formulas designed for digital sensors with autofocus motors. A 2024 Summilux-SL 50mm f/1.4 ASPH looks and weighs nothing like a 1935 Elmar 50mm f/3.5.

The eBay LTM vs L-mount Miscategorization Problem

Here's where buyers get hurt. eBay's category tree (and some sellers' product descriptions) routinely conflate "L-mount" with "LTM" because both abbreviations start with the letter L. You can find:

• A 1937 Summar 50mm f/2 LTM lens listed under "L-mount" or "Leica L-mount"
• A modern Sigma 24-70mm L-mount zoom listed under "M39" because the listing template used the wrong dropdown
• Japanese sellers describing a screw-mount Hektor as "Leica L mount" with no specific clarification
• A modern Panasonic L-mount lens described as "fits Leica" in a way that implies (but doesn't promise) M-mount or LTM compatibility

The two mounts are 89 years apart and physically completely different. They will not interchange in any way. An LTM lens has a 39mm-diameter male thread on its back. A modern L-mount lens has a four-flange bayonet with eleven electrical contact pins. They cannot be confused once you have one in your hands, yet they constantly are confused in eBay search results and category browsing.

How to Tell Mounts Apart from a Seller's Photo

Before bidding, look at the back of the lens in the listing photos. Each mount has a distinctive signature:

• LTM (L39, M39): A 39mm-diameter male screw thread on the rear, visible as a continuous spiral of metal threads. No bayonet flanges, no electrical contacts. Almost always all-metal construction in chrome, black paint, or nickel finish. Small overall, since most LTM 50mm lenses are under 50mm long.
• M-mount: A four-flange bayonet on the back. Look for the metal flanges that engage with the M body's bayonet ring. No electrical contacts on most older M lenses; modern 6-bit-coded M lenses have a coded ring (six small black/white squares) but still no electrical pins. Aluminum or brass construction, usually compact.
• R-mount: A bigger bayonet with deeper metal contours, designed for an SLR mirror box. Significantly larger throat opening than M-mount. Typically heavier and longer than an equivalent-focal-length M lens.
• L-mount: A four-flange bayonet (visually similar to M at first glance) BUT with a prominent ring of electrical contact pins on the rear, eleven gold pins arrayed around the inside of the mount. The lens body itself is usually larger, often plastic-skinned, sometimes with internal autofocus motors visible through vents. A 2020s L-mount Summicron-SL is approximately three times the size of an equivalent M-mount Summicron.
• TL-mount (same physical mount as L): Identical to L-mount physically; the labeling difference comes from whether the lens covers APS-C only (TL designation) or full frame (SL designation).
• S-mount: A much larger bayonet than any other Leica mount, sized for the 30×45mm sensor. If the lens is enormous, has a huge front element, and the listing says S2/S006/S007/S3, it's S-mount.

Two other quick heuristics: electrical contacts on the rear = modern (L-mount, TL, or S); no contacts = vintage (LTM, M, or R). And: screw thread on the rear = LTM, full stop. Every other Leica mount is bayonet.

Adapter Overview

Across all the mounts, the practical adapter situation is:

• LTM → M: Cheap and ubiquitous ($15–40). The M body's rangefinder reads the LTM lens correctly. Different adapter rings serve different focal lengths (the ring tells the M body which frame lines to show), so get the right one for your lens.
• LTM → L: Available but rare. The rangefinder/EVF on an SL body doesn't gain anything from a 1935 lens, but it can be done for the look.
• M → L: Common ($75–250 depending on quality). Leica makes an official adapter; third parties make cheaper ones. Mounts an M lens on an SL or other L-mount body with no electronic communication.
• R → M: Exists (Novoflex, Leitax) at $150–300. The adapter is a ~19mm spacer that brings the R lens to its correct flange distance on an M body. Caveat: R lenses have no rangefinder cam, so focusing requires Live View, which is practical only on M (Typ 240), M10, and M11. Pair with Leica's hot-shoe EVF (the EVF2, an Olympus VF-2 rebadge, for the M Typ 240; the Visoflex Typ 020 for the M10 generation; or the Visoflex 2 for the M11) for eye-level focusing with peaking and magnification, which makes the combination genuinely usable rather than awkward. On a film M or an M9 (no Live View), you'd be scale-focusing.
• R → L: Common ($75–200), and one of the more popular adapter combinations because R-mount lenses are cheap and excellent.
• S → anything: Closed system; no adapters exist for S lenses.
• L → anything older: Doesn't work mechanically. Modern L-mount lenses cannot mount on older Leica bodies because the body's FFD is too long.

The adapter market is mature enough that you can mount almost any Leica lens on almost any modern Leica body if you're willing to lose autofocus and electronic communication. Going the other direction, mounting a modern L-mount lens on an older Leica, is not possible.

Practical Implications for the Used Buyer

• If you're shopping for a vintage LTM lens, search "LTM" or "M39" or "L39," not "L-mount." Treat any "L-mount" listing skeptically until you've confirmed from the photos whether it's a 1935 Elmar or a 2024 Summilux-SL.
• If you're shopping for a modern L-mount lens, filter for full-frame coverage (lenses for the SL series) and look for the electrical-contact-pin signature in the photos. The lens should be physically large with autofocus and electrical contacts.
• If you're shopping for M-mount, the category is generally well-labeled, since sellers tend to know the M designation. Cross-reference with the four-flange bayonet visible in photos.
• If you're shopping for R-mount, verify the cam configuration from the back-of-lens photo before bidding. R-mount lens compatibility with different R bodies depends on which cams are present.
• If you're shopping for S-mount, the system is small enough that confusion is rare, but the prices are high enough that a verification photo is worth requesting before bidding.

The bottom line: Leica's mount history spans a hundred years and four major bayonet systems plus one screw mount. The eBay category tree is not a reliable guide to which mount a given lens uses. Look at the back of the lens in the seller's photos before you bid, and when in doubt, ask the seller for an additional photo of the rear mount.

Browse current LTM, M-mount, R-mount, L-mount, and S-mount lens listings on UsedLensTracker.