Archived posting to the Leica Users Group, 1999/12/04[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
Flare and unsharpness gradient. The general idea of flare in fact consists of three distinct phenomena. Stray light or veiling glare, that is unwanted light that is distributed over the whole image area and reduces contrast and lightens up the deeper shadows. Then we have secondary or ghost images that are caused by small lightsources, that are reflected by lens surfaces. And then we have halos around point sources as when we take night pictures of lampposts that are surrounded by a strong halo. Secular highlights also are affected by this as highlight details are washed out. Of course these phenomena are not unrelated, but have different manifestations. The 2.8/180 does not exhibit any stray light, blacks are deep dark and lightsources are very tightly delineated. Specular highlights show finely graded shades of white and secondary reflections are only observable under very unfavorable and seldomly encountered circumstances. The 2/180 again does not have any stray light and for such a lens it is amazingly well behaved here. Halos are also very well suppressed although a shade less than the 2.8/180. Secondary images can be seen when shooting straight into the sun or another strong light source. When the light source is just outside the image area, and very oblique, then we may see in certain but not all situations, a veiling glare that can be distractive. The excellent suppression of stray light shows in the details that hold contrast and gradation. This topic should be approached with some care. It is always possible to force a lens in a situation where flare of whatever character will be visible. Both 180 lenses are extremely well shielded from flare, and one really needs to some optical aerobics to induce flare, and then only in the area of ghost images and bright spots of some extension. In 99% of situations both these lenses can be used without any consideration for glare. The sharpness/unsharpness gradient is obviously related to depth of field. It is not well known that the DoF extension (distance before and after the sharpness plane) only depends on the reproduction factor. That is, when two objects are photographed such they they are of equal magnification, irrespective of the focal length, the DoF is identical. In practical terms, an object taken with a 35 mm at 3,5 meter and the same object taken with a 180mm at 18 meter will have identical DoF. So if we wish to compare the unsharpness impression of two different lenses, or make any general statements. we should take care to compare pictures taken at equal magnifications. Finer points of difference between the 2.8 and 2 version is the somewhat smoother gradient of the 2.0 lens. At the same reproduction factor and same distance before/behind the subject, the detail rendition of the 2.8 is slightly harsh, that is outlines of detail are quite crisp. maybe a bit over-crisp. The 2.0 produces a bit more washed out patches of color. The wider aperture is responsible for a big part of course here. When stopping down to 2.8 the Summicron approaches the Elmarit, but stays on the soft/fuzzy side of detail outlines. Whatever you prefer, you need to do some careful comparison here to make up your mind. There is a character difference here, base partly on the correctional choices. The Summicron might reproduce the background unsharpness a bit less pronounced and so help focus on the main subject. I am doing a major research project on these topics, so please see these notes as preliminary and not definitive. As general conclusion I may note that the 2.8/180 is by a small notch the best, closely followed by the 2/180 which has a slightly different character of rendition and by some distance the 180 position of the 70-180 vario lens. The 180 is a premium focal length and Zeiss with a 2/200, Canon with a 1.8/200 show what their designers can do when reigns are loosened. Within the R line these two lenses would be enough to convince anyone to try the Leica R for optical prowess. Erwin Please note that my reports are copyright protected.