俺在坛子里多处求证，未得其果。今偶见一篇文章详细介绍了50/2历代版本的变迁和特点，俺试着翻译出来供大家参考。
50/2 Summicron Many variations, so it can get confusing. Many consider the 50 Summicron best of all 50 mm lenses, by any manufacturer. It's the standard that other 50's are judged by. （50/2 Summicron有许多版本，所以常使人感到混淆。许多人认为50 Summicron是所有厂家的所有50mm镜头中最好的。它是评判其他50mm镜头的标准。）
· First version 1954-1957 Collapsible chrome. A good lens, but not as good as the later lenses. EXTREMELY likely to be found with lens scratches. It has a VERY soft front coating. Likely to be encountered fogged from original owner, see Fogging. Not collapsible on M5 or CL due to meter constrictions. 7 elements, focused to 40"（第一版，1954-1957年生产，银色缩头。好头，但还是没有后来的好。他前面的镀膜非常的软。很容易在第一用家手上就被不小心弄花了。因为测光器的原因在M5和CL上不能缩回。7片，最近对焦距离4英尺。）
· Second version 1956-68 Rigid chrome, although a few were made in black by special order. Aesthetically a very handsome lens, sought after by shooters and collectors. This lens was tested to have the highest resolution (at the expense of some contrast) of any 50 Summicron several years ago by a Japanese photography magazine. Again, very prone to front lens scratches. For many years thought to be the same optical formula as the collapsible, recently it has been confirmed to be slightly different. Likely to be encountered fogged from original owner, see Fogging. 7 elements, focused to 40" （第二版，1956-1968年，银色刚性rigid头，有极少数特别定制的黑色头。从美学角度来说是一颗非常英俊的头，它是摄影家和收藏家追寻的对象。几年前一家日本摄影杂志的测试表明此头在所有的50 Summicron镜头中具有最高的分辨率。仍然是前片容易花。许多年来人们都认为它的光学设计同前一版缩头是完全一样的，近来才被确认与前一版有轻微的不同。很容易在第一用家手上就被不小心弄花。7片，最近对焦距离4英尺。）
· Third version 1956-1968 Dual Range Summicron, chrome. This is a special close focusing version of # 2 above. The 50/2 Duel Range Summicron had the highest tested resolution of any lens ever tested by the great and sadly departed American photography magazine, Modern Photography. It has the closest RF coupled focusing of any M lens. 7 elements. Most "experts" say the optical formula is the same as the rigid, but many experienced DR users claim they get different results and so believe they must be different formulas. With a flat platform for the "eyes" on the top of it's focusing barrel, the DR is not as pleasing aesthetically as the rigid. Nevertheless, the DR is very sought after by shooters. Again, very prone to front lens scratches and also fogging if bought from the original owner, see Fogging. for Pics （第三版1956-1968双区间DR Summicron，银色。此头是第二版的近距对焦特别版。已经停刊的美国摄影杂志——现代摄影杂志测试表明50/2 DR Summicron镜头在所有测试过的镜头中具有最高的分辨率。它在所有M镜头中组合取景对焦距离最近。7片。大多数“专家”都说他与第二版rigid头的光学设计一样，但许多有经验的DR用家都声称它们具有不同的效果从而坚信其光学设计的不同。DR镜头的对焦筒上方有一个安装“眼镜”的平台显得不如上一版美观。无论如何，DR也是摄影家们追逐的对象。同样是前片容易擦伤，如果是从第一用家手上买来同样会花。）
The 50/2 DR will probably work fine on the M6, but you must remember to mount and dismount the lens focused at infinity. When focused near it's closest regular focusing distance, the lens will be difficult to mount OR unmount. I have reports of the DR not functioning in close up range on a M6. I am frankly unsure if these reports are due to variations with the bodies and the DR, or are the result of user error. More research will till. It seems prudent to try a DR on your M6 before you buy it. （50/2 DR 可能会在M6上工作得很好，但是你切记装卸镜头时要将镜头调焦到无限远。当调焦到接近它的常规对焦距离的最近端时它将难以装卸。我有关于DR镜头在M6上近距不能工作的报告，但我不能确定这些报告是因为机身、镜头不同还是错误使用的原因。我将做更多的研究。谨慎的做法是买DR之前在你的M6上试一试。）
Howard Cummer in Hong Kong reports difficulty using a 2nd series DR in close-up range on a M6 .85 # 2296539. While he could mount the lens, if it was not focused at it's closest regular focusing distance, the close up range was inoperative due to some sort of internal body restrictions. Whether this is true of all late M6's in general, or of just the .85 model is not clear at this time. In any case, it's a good idea to try it out to be sure on your own body/lens combination. （香港的Howard Cummer先生报告说在他的号码为#2296539的M6 0.85上使用第二代DR镜在用近距对焦时有问题。他能装上镜头，如果不能在常规对焦区间的最近端对焦，那么近距对焦就不能工作，原因是机身内部的某种限制。目前还不清楚这种情况是M6的普遍情况还是仅对0.85。无论如何，用你自己的机身/镜头组合试一试是个好主意。）
The 50/2 DR will NOT work on a Minolta CLE in my experience. Although the lens will mount, it will bind with the body just slightly from the infinity marking. （根据我的经验50/2 DR不能用在美能达CLE上。虽然能装上，但装在一起后无限远的标记总差一点点。）
The DR lens has two focusing ranges, thus the brilliant name "Dual Range." The DR can ONLY be mounted on the camera without it's "eyes." The "eyes" are a detachable viewfinder which clips onto the top of the lens and in front of the camera's rangefinder/viewfinder. They look pretty much like the viewer built into the 135/2.8 or the M3 versions of the 35/2 and 2.8. Once mounted, the closer focusing range is attained by turning the lens to it's closest normal focusing point. Then attach the "eyes" which clip onto the lens. ONLY at this focus point can the eyes be attached and the closest focusing range attained. THEN pull the focusing barrel out slightly, and the lens barrel can be swung over farther to the left, to get into the close focusing range. It sounds more complicated than it really is in practice.（DR镜头有两个对焦区间，所以才有了这个“双区间”的名称。DR镜头只有拆掉“眼镜”才能装上。“眼镜”是个卡在镜头上方而且在相机的对焦取景器前面的可装拆的取景器。它看起来与135/2.8以及用于M3的35/2和2.8的观景器非常相像。一旦装上它后，只要将镜头转到普通的最近对焦距离处，就可获得更近的对焦。所以，只有在这个对焦位置才能把“眼镜”装上并且卡到位，同时可获得最近的对焦。然后轻轻将镜头的调焦筒拉出，镜筒就可以继续向左转动以获得更近的对焦距离。这听起来很复杂，实际操作并不复杂。）
It is worth noting that many experienced used find the DR Summicron not only their favorite 50, but their favorite lens, period. It has a combination of higher resolution and lower contrast and superb out of focus images. （许多资深用家发现DR Summicron 不仅是他们最喜欢的50mm镜头，更是他们最喜爱的镜头。它同时具有高分辨率、低反差和优美的焦外成像。）
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