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It looks like Tamron may be entering the world of fast supertelephoto lenses. Three different optical formulas have appeared in the same patent application from Tamron.</p>
<p><strong>Embodiment 1: 300mm F/2.8</strong></p>
<ul>
<li>Focal length: 304.799 mm</li>
<li>F No.: 2.8</li>
<li>ω: 3.997</li>
<li>Image height: 21.64 mm</li>
<li>Back focus: 70.1919 mm</li>
<li>Lens length: 298.38 mm</li>
</ul>
<p><strong>Embodiment 2: 400mm F/4</strong></p>
<ul>
<li>Focal length: 396.296 mm</li>
<li>F No.: 4.0</li>
<li>ω: 2.963</li>
<li>Image height: 21.64 mm</li>
<li>Back focus: 102.3549 mm</li>
<li>Lens length: 332.36 mm</li>
</ul>
<p><strong>Embodiment 3: 500mm F/4</strong></p>
<ul>
<li>Focal length: 485.045 mm</li>
<li>F No.: 4.001</li>
<li>ω: 2.530</li>
<li>Image height: 21.64 mm</li>
<li>Back focus: 125.2621 mm</li>
<li>Lens length: 420.001 mm</li>
</ul>
<p>I think a 400mm f/4 is a lens missing from everyone’s lineup. Apologies to the Canon 400mm f/4 DO IS II, but I think a non-DO version would likely cost less and could give equal or better performance at the expense of reduced size and weight. Maybe there’s an engineering reason that I am unaware of as to why a non-DO 400mm f/4 doesn’t exist for Canon’s EF mount.</p>
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