Cooke Series XV Convertible Anastigmat 6,8/312 mm, c. 1930-40

Taylor-Hobson, England. Later version without engraving inside on border of front lens, no. 307771, convertible lens set with 8 glass-air surfaces 6,8/12 ¼ in., image format exactly for 8 x 10 in., the original sunshade is needed for sharpness at the picture-corners, this minimizes starting coma by vignetting. For application of the single lenses on 8 x 10 in., front lens 16/26 ½ in. an extension of approx. 21 in. and aperture of 44 is need, for back lens 12,5/19 in. an extension of approx. 20 in. and aperture 32 is needed, because color coma on border starts. Single lenses are good for 5 x 7 in., on 8 x 10 in. strong stopping down is needed. All 4 lens parts can be screwed. With adapter ring, can be used as mounting ring, with caps and leather case. Ansel Adams used this kind of lens for his famous photograph "Moonrise over Hernandez". Important user lens in good condition!

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)