How to Use M42 Lenses with a Canon EOS DSLR

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As an alternative to expensive lenses, many people have fitted M42 (commonly called "Pentax screw thread") lenses to their Canon DSLRs. M42 lenses are plentiful, and often very inexpensive in comparison to their more modern counterparts, as they were fit to a ton of '60s and '70s 35mm SLRs. Unlike other mountings, they have a flange focal depth very close to that of the EOS, which means you don't lose the ability to focus to infinity.

These aren't usually useful for sports photography that requires rapid focusing, for example, because they are almost without exception manually focused.[1] Nor are they particularly good for quick snapshots, since shots can take a little while to set up. But sometimes, economy is important, or you might happen have a bunch of M42 lenses sitting around. Maybe you just want to see what photographs old lenses will take. If so, then it may be worth your time to try using one with your EOS digital SLR. Here's how.

http://www.wikihow.com/Use-M42-Lenses-with-a-Canon-EOS-DSLR

優秀なレンズが揃うM42マウント
http://plusd.itmedia.co.jp/d-style/articles/0711/22/news007.html

938fg8

印象中见过khonsou把蔡司头用在Canon 20D上。

疯人峰

需要对镜头进行手术，要不然打反光板。

DigiPub

レフ機構は広角レンズの場合ミラーの動作半径が窮屈になると思います。长焦的是不是不用做手术呢。

顺便介绍一个 トリビアな豆知識
现在的标准镜头对于35mm胶片画幅老说是指50mm的镜头，但最初的概念是与人眼视角一样的镜头。对于35mm来说，48mm镜头是标准镜头。但是因为，48mm的镜头的像距尺寸内无法装下反光镜机构。只好放弃，把数字整齐近似的50mm叫做标准镜头了。