Archived posting to the Leica Users Group, 1997/12/20
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>But actually, what I really objected to, was that the opinion is that long >lenses focus past infinity just because of the temperature drift. This is >not true. They focus past infinity so that a photographer, knowing the >proper focusing process, can indeed critically focus on very distant >objects with those very long lenses. This is not opinion, but fact. All long telephotos can be racked past the 'normal temperature infinity' position. All companies do this. Ask them. In the past, some companies have not provided enough distance past the normal infinity point. I've shot at -50 degrees celsius, and I've shot at 45 above (more when the sun hit lens). The differences in focus settings over this range of temperatures can be substantial. I've used telephotos (non-flourite, one mirror and one refractor) that didn't have enough 'past infinity' to focus on distant objects at very cold temperatures. That raised my personal temperature, but I didn't get the picture. So that is why camera companies design long lenses with spare helicoids 'past infinity', but practically speaking, you are correct. That's the way I focus too. Of course, if the temperature thing didn't happen, one infinity point could be built in, and once adjusted, you could focus on distant objects (depending on distance and actual focal length) just by setting the lens at the infinity mark. * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com