This highly sought-after micro lens was introduced in 1961. It can focus all the way from infinity down to only 10cm and achieve 1:1 magnification without extention tube.This lens can be attached to the bellows unit in reverse, producing an astonishing 4:1 magnification. The only problem is finding the rare M-B connecting tube required between bellows and lens front. It is also a well-known problem that the M-B tube may be stuck in the lens if over-tightened. There are around 2,500 units produced in two versions, starting with serial no. 171529. The first version has a recessed filter ring which makes it difficult to even just attaching a normal lens cap. (Unless you have the dedicated front cap with longer pins for this lens.) It was rectified with a protuded filter ring in the second version. A drawing of a prototype with "Tick marks" is shown in some early literature. The production version doesn't have any "Tick marks". I have not personally shot any picture with my 5.5cm Micro lens but I have heard good words about it. Most users claim this lens is razor sharp and outperforms many modern optics. You know, they just don't make thing like this anymore!
		The lens extends from 6.6cm to 12cm as its focus changes from infinity to minimum focus distance.