Encode Leica M lenses: Get the most out of your glass

Community tip: Macfilos’s in-depth article on 6-bit coding and EXIF tweaking for third-party lenses. Read the article.

Table of contents

1. What is 6-bit coding?
2. What exactly does coding do for you?
3. Which lenses benefit?
4. Methods compared
5. Step-by-step guide, including the complete code table
6. Common mistakes and practical tips

1. What is 6-bit coding?

Six tiny fields on the bayonet ring. Black or white. That’s enough for a digital Leica to identify the lens.

Leica introduced this system in 2006 with the M8, its first digital M camera. In the M system, there are no electrical contacts between the camera and lens. Instead, six recesses sit on the bayonet flange and are filled with either black or white paint. This creates a binary code: six positions, 64 possible combinations. The camera reads this code purely optically, using an infrared LED and a photosensor in the body.

Black absorbs infrared light (= 1), while white reflects it (= 0). The sensor reads the sequence clockwise, starting at the 12 o’clock position. It sounds simple and has worked reliably for almost 20 years.

Which cameras read the code? All digital Leica M bodies from the M8 (2006) onward: M8, M8.2, M9, M-E, M Monochrom, Typ 240, M-P, M10, M10-P, M10-R, M10 Monochrom, M11, M11-P, M11 Monochrom. On the SL2 and SL3, the code works via the original Leica M-Adapter L.

Newer Leica lenses (from around 2006 onward) already come coded from the factory. The recesses are machine-milled and permanently painted. Older Leica lenses, Voigtländer, Zeiss ZM, TTArtisan, 7Artisans, and other third-party lenses don’t have this code. That’s exactly where retroactive coding comes in.

2. What exactly does coding do for you?

Four things happen as soon as your camera identifies the lens. All four improve your shooting—some significantly, others subtly.

EXIF data: Order instead of guesswork

Without coding, the metadata shows “Unknown Lens” or nothing at all. Focal length and aperture: nowhere to be found. Anyone who uses 15 different lenses and wants to filter by lens in Lightroom knows the frustration. With coding, the camera automatically writes the correct lens model to every single file.

Automatic image correction: vignetting, color shift, distortion

This is the most tangible benefit. Digital Leica bodies store internal correction profiles for every coded lens. This corrects vignetting (the dark corners), chromatic aberration, and the notorious “Italian Flag” effect directly in the camera. Wide-angle lenses under 35mm benefit especially noticeably.

Smart coding for third-party lenses: Zeiss ZM 35mm f/2 Biogon? Code it as a Leica Summicron-M 35mm f/2 ASPH. The focal length and aperture match, and the vignetting correction is approximately right. It does not have to be perfect—the correction profile covers most of it.

IBIS on the SL2 and SL3: essential, not optional

This is the point many people underestimate. The Leica SL2 and SL3 have in-body image stabilization (IBIS). It absolutely needs the focal length to compensate correctly. Without coding, the camera guesses—or does not stabilize at all. If you mount a 90mm lens and the camera assumes 50mm, IBIS actively makes your image blurry.

Sure, you can set the focal length manually in the menu. If you forget after changing lenses, the next 200 pictures are throwaways. Coding solves this automatically. Do it once and never think about it again.

Adapter choice for the SL: The original Leica M-Adapter L passes the 6-bit code on to the SL. Many third-party adapters (e.g., from K&F Concept and TTArtisan) do not. If you want IBIS and automatic recognition, you need the original adapter.

Workflow: No more clicking through menus

Without coding: change the lens, open the menu, select the focal length manually, confirm, and go back. Annoying with three lens changes a day. Unbearable with ten. Coded lenses are recognized immediately—twist them onto the mount and start shooting.

Why you should definitely code your lenses (especially on the SL2/SL3)

Jonathan Harris from Worldwide Camera Exchange explains the benefits and demonstrates the coding process with the Akara kit.

3. Which lenses benefit?

Short answer: any M-mount lens without factory coding on any digital Leica.

Older Leica lenses (Pre-2006)

Summicron 50mm f/2 Version IV, Summilux 35mm f/1.4 Pre-ASPH, Elmarit 28mm f/2.8—the classics everyone knows and loves. Optically, they often hold their own against current designs. But on the M10 or M11, they remain “invisible” until you code them. The correction profiles turn an already good lens into an even better one.

Voigtländer VM/ZM

The Cosina-made Voigtländer lenses are the insider tip in the M universe. Nokton 35mm f/1.2, Ultron 35mm f/2, APO-Lanthar 50mm f/2—optically first-rate and available for a fraction of the price of Leica. Uncoded from the factory. Some newer models have slight grooves on the flange that help the applied paint adhere better. Code them as the next closest Leica equivalent (same focal length, similar aperture).

Zeiss ZM

Planar 50mm f/2, Biogon 35mm f/2, C Sonnar 50mm f/1.5. Zeiss has even published an official recommendation list showing which Leica profile matches which ZM lens. The PDF can be found on zeiss.com on the ZM product pages.

Chinese brands: TTArtisan, 7Artisans, Thypoch

Even inexpensive third-party lenses benefit enormously. TTArtisan 50mm f/1.4 on the M11 without a code: no EXIF, no correction, confusing IBIS on the SL. With a code: a completely different user experience. The correction profiles aren't perfect, but an 80% improvement over 0% is a clear win.

4. How does the code get onto the lens?

There are four ways. Each has its place, depending on your budget, skill level, and durability requirements.

The Leica tool is the premium option: milled recesses, professionally painted, including cleaning. That makes sense for a 5,000 EUR Noctilux. For a 300 EUR Voigtländer, not so much.

Match Technical offers replacement flanges with pre-milled coding recesses. A solid solution, but you have to partially disassemble the lens. Not for everyone.

For most users, an encoder kit is the sweet spot: snap on the precise stencil, color in the dots, and you're done. No tools, no disassembly. The paint holds up reliably in everyday use and can be removed without leaving residue if needed.

DIY with a Sharpie and paper template works, but it's fiddlier than it sounds. Hitting the exact positions without a stencil requires patience. And most felt-tip pens are too glossy for the IR sensor.

5. Step by step: Coding with the Ausgeknipst Encoder Kit

Step 1: Look up the code

Find your lens in the code table (included with the kit and also available on our product page). Third-party lens? Choose the Leica lens with the same focal length and a similar maximum aperture.

Disclaimer: We sell some of the products linked here ourselves.

Step 2: Clip on the encoder

Place the encoder on the bayonet flange and snap it into place. The template fits precisely and shows you the six positions. Nothing wobbles.

Step 3: Paint the dots

Use the included Edding 8400 to fill in the black fields according to the code. Leave the white fields blank; the bare metal correctly reflects the IR light. One dot takes one second.

Step 4: Remove and test the encoder

Remove the template and mount the lens on the camera. The correct lens should now be displayed in the menu or Live View. If not, touch up the dots and make sure no black has spilled onto a white field.

Screw at a coding position? Some lenses have a retaining screw at one of the six positions. No problem: Fill the screw with a dab of white paint or nail polish. If the code calls for a black dot there, simply paint over it in black after it has dried.

Complete 6-bit code table

Find your lens (or the closest Leica equivalent) and read off the code. Position 1 is the 12 o'clock recess; position 6 is the next one clockwise.

Legend: ○ = White (no color/metal) | ● = Black (paint)

On smartphones: scroll the table horizontally. The “Frame” column shows the bright-line frame display in the viewfinder—not relevant to the coding itself, but useful as a reference.

6-bit coding explained and demonstrated

Dr. Scott McDonald demonstrates the coding with a paper template and Sharpie, and explains what the camera does with it.

6-Bit Encoder Kit & Specialty Pen for Leica M & SL (EUR 39.95)

6. Common mistakes and practical tips

Mistake No. 1: Wrong pen

The most common reason why even self-coded lenses aren't recognized. Standard felt-tip pens and Eddings are glossy, and the reflected light fools the IR sensor. It reads “White” instead of “Black.” The solution: a pen with matte, infrared-absorbing ink. The Edding 8400 (Aerospace Marker) is made for this—waterproof, lightfast, and above all: matte. That's exactly why it's included in our kit.

Mistake No. 2: Choosing the wrong code

If you code a Voigtländer 40mm f/1.2 as a Leica 50mm f/2, you get functioning EXIF data, but the vignetting correction isn't optimal. The best approach is to match the focal length and maximum aperture as closely as possible. Coding a 40mm lens as 35mm or 50mm is perfectly fine as long as the aperture values are similar.

Mistake No. 3: Forgetting to adjust IBIS manually

Anyone working without coding on the SL2/SL3 who forgets to change the focal length in the menu after changing lenses will systematically produce blurry images. The IBIS then compensates for the wrong focal length. This doesn't happen with coding.

Mistake No. 4: Third-party adapters on the SL

Not every M-to-L adapter passes on the 6-bit code. Only the original Leica M-Adapter L (and a few selected third-party options, such as Novoflex with newer firmware) transfer the coding. K&F, TTArtisan, and many eBay adapters do not.

Code table for third-party lenses: Do you have a lens that doesn't appear in any Leica list? Choose the Leica model with the identical focal length. If the focal length is the same but the aperture differs: lean toward the slower lens (e.g., code an f/1.2 as f/1.4). The vignetting correction for the slower lens is slightly stronger; too much is better than too little.

Mistake No. 5: Applying the code to film cameras

6-Bit coding has no effect on analog Leica M bodies (M6, M7, MP, M-A). The cameras have no sensor to read it. Applying it does no harm, but it does nothing. Save yourself the effort.

Mistake No. 6: Not allowing the paint to dry properly

If you mount the lens on the camera immediately after coloring it in, you risk smearing paint on the bayonet ring. Allowing 60 seconds of drying time is enough. The Edding-8400 ink dries quickly but must cure completely. It is then wipe-resistant.

How to remove the coding: If you want to change or undo the code: apply isopropanol (IPA) to a cotton swab and wipe off the dots. The Edding-8400 ink dissolves without leaving any residue. You can then apply a new code or use the lens uncoded.

Further resources

The community has compiled a wealth of material. Here are the best sources:

• Macfilos: Third-Party Lenses on Steroids with 6-Bit Coding. Very detailed article with practical examples
• Moritz Recke: Adding 6-Bit Coding to Leica M Lenses. Step-by-step DIY guide
• Yukosteel: Leica M Lenses Auto Detection System. Technical deep dive into the sensor mechanism
• Rangefinderforum: 6-Bit code list. Complete code table with community additions

Get started right away? Encoder Kit with special pen, everything you need included. Suitable for every M-mount lens. View the 6-Bit Encoder Kit.

More guides? Film scanner comparisons, camera repair tips, and practical analog photography advice. All blog articles.

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