Archived posting to the Leica Users Group, 1999/10/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]The 4.5/15. At full aperture this lens has a medium overall contrast, Distortion is surprisingly low, only a bit barrel distortion, but some severe light fall off. But for a 15mm that is acceptable. On axis we see a crisp definition of very fine detail over an image circle of 6mm diameter. Beyond that image quality drops fairly rapidly. At an image location, 6 mm from center, very fine detail has quite soft edges, but they be detected without difficulty. Going from here to the corners the very fine detail becomes quite fuzzy, but stays within visible range. Fine detail is rendered with good visibility. The detail rendition is a bit dull. There is some serious flare that lowers contrast. Astigmatism and curvature of field are well corrected. In the field however the chromatic errors (longitudinal) are quite visible as color fringes around edges. There is a trace of decentring. Corner and edge performance is good. Stopping down to 5.6 crispens the whole image a bit and fine detail is recorded now with good edge contrast. The overall improvement is slight but noticeable and now very fine detail is recorded over most of the image field. This aperture is the optimum one. Close-up performance (1 meter) is excellent and about equal to the infinity setting. At 1:8 image quality drops, as contrast takes a dip. Vignetting is now almost invisible. At 1:11 the contrast drops rapidly, reducing the image quality to barely useable. There is some reason why Zeiss stops at f/8!! This is a very good, if not excellent lens, with a high level recording capacity on axis and a good one in the field. The details are a bit muddy and miss the clarity that characterizes the Leica lenses. Perspective. I have now tested the 4.5/15, the 4/25 and the Nokton 1.5/50 and all three show some interesting family characteristics. All have decentring, sometimes degrading the image quality more than should be tolerable for high quality imagery. All have flare, pointing to a coating technique that could be improved. And all have a somewhat dull, flat rendition of details and outlines. This points to glass selection and a certain choice of aberration correction. On the positive side I note an excellent sometimes outstanding behavior on axis, and a very good to excellent performance in the field. (when filtering away the decentring problem). All three give better imagery than first class lenses 10 years ago and clearly show the direction of the Cosina designers: Astounding value for the money. I personally dislike the borrowing of the outward design of the Zeiss Contax G and the older Leica lenses. But if you have to choose between optical design and industrial design when you are on a tight budget, this is a sound choice. Erwin