Archived posting to the Leica Users Group, 1997/05/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>With the Summicrons point light sources (stars, street lamps in the >distance) became elongated. This started to happen about half way from >the center of the pictures towards the borders. This effect I called >coma. What term is the correct to use? > Without having seen the pictures I must guess. Are the light sources sharply in focus? What you describe seems to me the effect of halo around light sources. And that is quite normal. The film you used is also a factor of influence. 'Coma" you can recognize as distinct and asymmetrical triangles of light, like the tail of a comet. Mostly the light patch fades away in one direction. There is also another form of coma, which has an elliptical shape. If astigmatism also is present, then the figure may look like the infinity symbol, a horizontal '8'. So it is quite difficult to tell from the figure what if any lensfault is present. There are so many variables, as you said yourself, that it not easy to diagnose the quality of a lens. Erwin Puts