Experimental Calculation Dagor Series III A 5.5/240 mm, 1908 onw

C.P. Goerz, Berlin. Only known example of the Series IIIA, no. 252270, lens halves classically cemented in three parts as with the 1:6.8 Dagor, brass mount with iris diaphragm and English aperture values 5.5–8, 11–16, 22–32, 45–64, original engraved in brass on the side "Unverk?uflich" (not for sale), with screw ring and octagonal presentation board. – Testing: Focal length approx. 238.9 mm, aperture f/5.5 correct, the angle of view for image sharpness in line with modern large-format users is 66 degrees and is vignetting-free from f/16 onwards for the 310mm image circle, the field curvature at infinity is 2.5 mm from the center to the edge of the image circle, the illumination extends beyond 66 degrees without point-source sharpness. The reason for Goerz's non-marketing of this lens most likely lies in the varying coefficients of thermal expansion of the sophisticated glass types used (some patents of the time indicate that these glass types fluctuated depending on the batch, requiring expensive recalculations), which led to fine lines in the cemented joints that become highly visible under point light. However, it is possible to license this type of 1:5.5 lens, which was used as the ICA Maximar or Meyer Double Anastigmat, where the same familiar form of cement defect also occurs in some of these lenses. However, cement types are known in even faster lenses of the Dagor type, which are based not on Canada balsam but on shellac (suitable for space industry). This is a museum piece of high standing for an optics museum, where it can be shown that better technology was possible even before 1914, but materials science had not yet advanced that far. Photographs can also be taken with this lens, al-though not for every subject (some soft-focus overexposure in highlights due to the lines in the cement), but the intended technical performance can be clearly demonstrated.

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)