Canon Patent: Converter Lens For EF-S 24mm F2.8 STM (increases focal length)

Canon Patent

I am not 100% sure I got this Canon patent application right. It seems to be about a magnifying optical system that increases the focal length.

The converter discussed in the patent literature appears to refer to the EF-S 24mm F2.8 STM lens (the master lens). From the patent literature:


A rear converter lens (hereinafter referred to as a converter lens) capable of enlarging the focal length of the entire system (increasing the focal length) by being placed between an interchangeable lens and an imaging device. It has been known.

In general, a converter lens has a negative refractive power, and the negative refractive power tends to increase as the magnification of the focal length increases. It is also known that if the curvature of the negative lens in the converter lens is increased in order to increase the negative refractive power, various aberrations such as coma due to the off-axis light flux are likely to occur.

In view of such problems, an object of the present invention is to provide a converter lens capable of obtaining high optical characteristics in the entire system when arranged on the image side of the master lens.

Master lens

  • Focal length: 24.50
  • F-value: 2.88
  • Half angle of view: 29.14
  • Image height: 13.66
  • Overall length: 64.83
  • Back focus: 35.68

Example 1

  • Focal Length: 39.54
  • F-value: 4.65
  • Half angle of view: 28.68
  • Image height: 21.64
  • Overall length: 89.59
  • Back focus: 13.96

Example 2

  • Focal length: 49.27
  • F-value: 5.79
  • Half angle of view: 23.71
  • Image height: 21.64
  • Overall length: 97.18
  • Back focus: 11.00

More Canon patent applications are listed here.

Sigma Announced Mount Converter MC-21, Pricing and Availability

Mount Converter MC-21

Available April 2019, the Sigma MC-21 can already be pre-ordered.

Sigma MC-21 Mount Converter/Lens Adapter (Canon EF-Mount Lenses to Leica L) – $249 – B&H Photo | Adorama.

Sigma Announces Pricing & Availability for Sigma Mount Converter MC-21

Available in April 2019, the new accessory ensures compatibility of the Sigma lenses in EF and SA mounts with the L-Mount camera systems.

Ronkonkoma, NY – March 29, 2019 – Sigma Corporation of America, a leading still photo and cinema lens, camera, flash and accessory manufacturer, today announced pricing and availability for the new Sigma Mount Converter MC-21, offering photographers a wider range of lens options for L-Mount cameras from Sigma, Leica and Panasonic. The SigmaMC-21 will start shipping in April 2019 and will be priced at $169.00 USD for Sigma SA-L mount and $249.00 USD for Canon EF-L mount.

The Sigma Mount Converter MC-21 allows for Sigma’s SA mount and Canon EF mount lenses to be used on L-Mount camera bodies. By attaching MC-21 to a Sigma SA mount or Sigma Canon EF mount lens, it becomes compatible with the L-Mount camera system without compromising usability and image quality. The development of Sigma MC-21 increases the number of interchangeable lenses manufactured by Sigma to be used with the L-Mount systems by 29, offering a total of 40 lens choices, including 11 DG Art primes with native L-mount. The addition of MC-21 to the Sigma accessory lineup will increase the accessibility of the L-Mount system and further Sigma’s role in the strategic L-Mount Alliance alongside Leica and Panasonic.

The full list of compatible lenses and technical specifications can be accessed here and product imagery can be downloaded here.

The lower price for the Sigma MC-21 in Sigma SA-L mount reflects the company’s appreciation for the loyal Sigma camera users as the MC-21 in Sigma SA-L mount allows for Sigma SA mount lenses to be used on any L-Mount camera body. Eventually, Sigma will aim to replace its SA mount lenses with the native L-mount versions, but until then, Foveon shooters can rely on the existing offering of Sigma MC-21 at a lower price point to ease the transition to the new system.