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This is the first I have seen this sort of patent. Canon has filed an optical formula patent for a diffractive optic macro lens. What better lens to upgrade with a DO version than the long-in-the-tooth Canon EF 180 f/3.5L Macro?</p>
<p style="color: #444444;"><strong>Patent Information (Google Translated)
</strong></p>
<ul style="color: #444444;">
<li>Patent Publication No. 2014-137484
<ul>
<li>Publication date 2014.7.28</li>
<li>Filing date 2013.1.17</li>
</ul>
</li>
<li>Example 1
<ul>
<li>Focal length f = 180.00mm</li>
<li>Shooting magnification ∞ 0.5x 1.0x</li>
<li>Fno. 3.50-4.50-5.20</li>
<li>Half angle ω = 6.85 °</li>
<li>Image height 21.64mm</li>
<li>The overall length of the lens 202.38mm</li>
<li>BF 52.18mm</li>
</ul>
</li>
</ul>
<p>Source: [<a href="http://egami.blog.so-net.ne.jp/2014-07-29" target="_blank">EG</a>]</p>
<p><strong><span style="color: #ff0000;">c</span>r</strong></p>
