Archived posting to the Leica Users Group, 2001/01/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I explored the limits with my new Leicaflex (Mark1) and 50 Summicron and 90 Elmarit lenses in 1968. Like the testers in Camera 35 magazine, I used the United States Bureau of Standard lens testing charts and directions, but instead of using Pan-X film, I used Kodak High contrast Copy film and H&W Control developer. I tested the lenses at 76 focal lengths, which provided a maximum possible resolution of 240l/mm, or 120lp/mm. Results: The highest resolution was achieved with the Summicron at f4 in the center of the image, where the resolution was an astounding 240 l/mm (120lp/mm)! I could only see this resolution with a microscope. When I put the negative in the focomat 1C and checked resolution at 8X and at f4.5 with my Focotar, I could not see this level of resolution, but not because of the quality of the lens, but because of the low level of magnification. At 16x, I could just barely make out the resolution lines. My conclusion: just like Erwin, there is a point of diminishing returns, and for normal superb quality, 80l/mm (40lp/mm) is certainly it. Ctein states that about 5 lp/mm in the print is needed to get satisfactory sharpness, but one needs 30 lp/mm on the paper to achieve optimum sharpness - read resolution of the image structure = grain. This can be achieved with the best enlarging lenses. The best resolution across the field was at f5.6 with both lenses, and at this aperture resolution across the filed was from 160 to 200+ l/mm (80-100 lp/mm). I tested some other normal lenses, and the best was the 50mm f1.4 Nikor, which achieved 160 l/mm (80lp/mm) across the field at f5.6. To achieve uniform performance across the field. all of the lenses I tested should be stopped down to f8- f9.5. At this aperture diffraction evens out optical performance, and at f11 performance levels out at about 68-80 l/mm (34-40 lp/mm) but with reduction in contrast. More recently, I checked my lenses with the USBS charts at 26 focal lengths which results in a maximum possible resolution of 80 l/mm (40 lp/mm). the best lenses in my current stable are the ancient 90 Elmarit, the 60mm Macro Elmarit - -R and the100 APO Macro Elmarit-R. the APO lens is the best lens I have tested. The resolution lines are etched on the negative right across the field from f2.8 until diffraction takes its toll. I plan on testing all of my lenses later this winter with Tech Pan film, Technidol developer, and at 76 focal lengths. I'll share my results with you. Ferrel Anderson