Quick answer

Mount a Leica 43mm IR filter when you want the classic infrared look—dark skies, glowing foliage—on infrared film, and remove it for normal visible-light shots. The filter blocks visible light, so meter and focus with infrared compensation rather than trusting your camera's standard readings.

Why the filter is only half the job

Infrared film is sensitive to both visible and infrared light. Without a filter, the visible light dominates and you get a near-normal image. An IR filter cuts most visible light so the infrared response can show through. That is why the filter is not optional for the classic look—it is the control that makes the film behave predictably.

The trade-off is exposure. Because the filter removes so much light, you need wider apertures, slower shutter speeds, or a tripod. Plan for longer exposures than you would use with the same film and lens without a filter.

Match the filter to your lens, not just the camera

The 43mm figure is the filter thread diameter, not a Leica model number. Check the front of your lens or its instruction sheet for the filter thread size before buying. A 43mm filter fits lenses with a 43mm thread; step-up rings can adapt it to larger threads, but they add depth and can cause vignetting on wide lenses.

If you shoot with several lenses, decide whether one 43mm filter plus step-up rings is enough or whether you need a second filter in a larger size. The filter is small and easy to carry, but swapping rings in the field costs time.

When not to use an IR filter

Skip the filter when you want a normal visible-light image, when light is already very low and you cannot use a tripod, or when you are shooting color infrared film that already has strong filtration built into its workflow. Also skip it if your only lens has a different thread size and you do not have a safe step-up ring.

If you are unsure whether a scene will benefit, shoot one frame with the filter and one without. Infrared film is expensive enough that a test frame is cheaper than a wasted roll.

Step-by-step: shooting infrared film with a 43mm IR filter

  1. Confirm the thread size: Check your lens front or spec sheet for a 43mm filter thread. Screw the filter on gently until snug—do not overtighten, especially on older metal threads. If the filter does not start easily, stop; cross-threading can damage the lens thread.
  2. Load infrared film in subdued light: Load and unload the camera in shade or indoors, not direct sun. Infrared film can fog through the film gate or light seals if exposed to strong light before development. Keep the camera closed and avoid pointing the lens at the sun with the filter off.
  3. Meter without the filter, then compensate: Take a meter reading without the filter, then add the filter factor recommended by the film or filter maker. If no factor is supplied, bracket exposures by one stop around your best guess. Do not trust through-the-lens metering with a deep IR filter; it often underexposes because the meter is not sensitive to infrared.
  4. Focus and adjust for infrared shift: Focus normally, then shift the focus ring slightly toward the infrared mark if your lens has one. If it does not, stop down to f/8 or smaller to gain depth of field and reduce focus error. Wide apertures plus infrared focus shift can produce soft images; test one frame at working aperture before committing a whole roll.
  5. Shoot a bracket and note your settings: For each scene, shoot one frame at your calculated exposure and one or two frames at ±1 stop. Record the filter, aperture, and shutter speed so you can repeat what works. Infrared film response varies with lighting and development; your notes are the only reliable guide for next time.
  6. Remove the filter for visible-light frames: If you switch back to normal film or want a visible-light reference frame, unscrew the filter and store it in its case. Do not leave it on the lens in bright sun when not shooting infrared. A filter left on the lens is easy to forget; check the front of the lens before every shot.

Product facts