1), corresponding to a lens with an infinite entrance pupil diameter. In practice, that cannot be reached due to mechanical constraints of the camera system (shutter clearance, mount diameter). Even for systems that can be designed without significant constraints on lens size and image plane distance (e.g. microscopy and photolithography systems), the cost of going beyond a numerical aperture of 0.95 (f/0.164) is usually prohibitive. In SLR camera systems, typical mount diameters are in the range of 44–54 mm, with flange distances around 45 mm. This limits the maximum possible f-number to 1.0 to 1.2, with rather strong vignetting towards the edges of the image. Flange distances are significantly smaller for rangefinder and mirrorless cameras (even below 20 mm), theoretically enabling designs down to something like f/0.7 or even faster. The chance of seeing these in practice will be slim, since their cost and weight are likely not competitive with respect to equivalent imaging solutions employing larger sensors. List of ultrafast lenses Some of the fastest camera lenses in production were as follows: Cosina Voigtländer Nokton 10.5mm, 17.5mm, 25mm, 42.5mm, 60mm 0.95 for Micro Four Thirds mount Vantage One T1.0 Cine lenses from 17.5mm to 120mm (Super35mm Spherical Primes) SLR Magic 25mm T/0.95 Cosina Voigtländer Super Nokton 29mm 0.8 Micro Four Thirds mount SLR Magic 35mm T/0.95 Handevision Ibelux 40mm 0.85 (made for Micro Four Thirds and various APS camera mounts, including Sony E-Mount and Fujifilm X-Mount) Fujinon 43mm 0.85 Leica Noctilux-M 50mm 0.95 ASPH (announced on September 15, 2008, then the fastest aspherical lens to have reached mass production; MSRP of £6290 or approximately US$10,000). Zhongyi Mitakon 50mm and 35mm 0.95 in various optical versions and mounts, of which at least the 50mm for Leica M rangefinders has been found to in fact only be 1.06! Nikon Noct-Nikkor Z 58mm 0.95 The following lenses are no longer in production : American Optical 81mm 3.259" 0.38 Solid Schmidt Mirror lens (designed for aerial reconnaissance, documented in 1967, but most likely never built) GOI CV 20mm 0.5 Mirror lens (2.9 mm image diameter, 1948; design and glass types used are well documented for anyone wanting to build their own Signal Corps Engineering 33mm 0.6 GOI Iskra-3 72mm 0.65 Mirror lens Fujinon-IDEAX 125mm 0.67 and/or 0.85 (X-ray lens, two speeds quoted on front ring) Zeiss Planar 50mm 0.7 (Limited 10-copies production for the NASA space program, later used on 35mm movie cameras