Busch Double-Speed Petzval-Type Portrait Lens, after 1872

Rath. Opt. Ind. Anst. formerly Emil Busch, Rathenow, Prussia. Engraved on the side "Portr. 48 4." (indicates the lens diameter in Parisian lines). Diameter of the lenses, glass only, 104 mm. Focal length is 260 mm. If the later-added aperture mount is removed, this would be 2.5/260 mm. The slot width for apertures is 90 mm. The internal diameter is limited to 75 mm, which would be 3.4/260 mm. Height with lens hood: 21.5 cm, all threads are working. There are some marks on the outermost edge of the front lens. Under point light, the interior is good except for some small scratches that are insignificant for practical use. Distance between rear element and focusing screen at infinity: approx. 15 cm, weight with screw ring 4.16 kg, Extremely rare

布雷克拍品等级是为了方便竞买人判断拍卖品的成色而设置的。布雷克等级用1到6级来标注外观和功能的成色，(从非常好到非常差)。 在目录图册里用括号里的2个数字来表示，前一个数字表示外观成色的级别，后一个数字表示功能成色的级别。如(3/2)表示外观成色是3(满意的)，功能成色2(好)。 成色 定义参照下列标准： 1 - 非常好 (未使用过，没有使用痕迹) 2 - 好 (新，极少的使用痕迹) 3 - 满意的 (普通的使用痕迹) 4 - 及格的 (明显的使用痕迹，某个非主要部件是后配的) 5 - 有缺陷的 (极明显的使用痕迹, 某个主要部件是后配的，功能上有缺陷，需要修理) 6 - 非常差 (严重破损, 缺少重要部件)