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Fujinon XF 50-140mm F2.8 R LM WR:
B&H Photo /Amazon / Adorama

A Sigma 50-140mm f/2.8 patent has been found that would be similar to Fujifilm’s Fujinon XF 50-140mm F2.8 R LM WR lens for X-mount. If Sigma brings a 70-200mm f/2.8 equivalent lens to market it will be interesting to see how they differentiate it from the Fujinon XF 50-140mm F2.8 R LM WR.

• Applicant: Sigma Co., Ltd.
  Publication number: P2023090116
  Application number: P 2021204904
  Publication date: 2023-06-29Title
  of invention: Imaging optical system
• Kind Code: A1 A compact image forming optical system having a small open F value over the entire zoom range is provided.
• Since the body of the mirrorless camera has been downsized by eliminating the mirror, downsizing of the imaging optical system is required accordingly. Also, there is a demand for a large aperture zoom lens with a small open F-number over the entire zoom range.
• Patent Document 1 discloses a positive lead type zoom lens having a bright open F number of about 2.8 and having a lens group closest to the object side fixed with respect to an image plane during zooming. Since the optical total length does not change, convenience and robustness are high, but there is a problem that the size of the imaging optical system is large.
• Patent Document 2 discloses a positive lead type zoom lens having a bright open F number of about 2.8 and a shortened optical overall length at the wide-angle end. However, since many lens groups with large diameters that move during zooming are arranged on the image side of the aperture stop, the mechanism required for zooming is large, and the size of the lens barrel in the radial direction is large. .
• SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact imaging optical system with a small open F-number over the entire zoom range.

• Example 1 (for 50-140mm F2.8 APS-C)
  Zoom ratio 2.70
  Wide angle Medium Telephoto
  focal length 50.50 85.38 136.50
  F number 2.92 2.92 2.92
  Total angle of view 30.62 18.00 11.40 Image height 14.20
  14.20 14.20
  Lens length 125. 00 137.38 145.00

• Example 2 (for 70-200mm F2.8 full size)
  Zoom ratio 2.70
  Wide angle Medium Telephoto
  focal length 72.00 122.00 194.10
  F number 2.92 2.92 2.92
  Full angle of view 32.92 19.26 12.12
  Image height 21.63 21.63 21.63
  Lens length 168.0 0 190.61 203.60

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