Archived posting to the Leica Users Group, 2006/01/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]The filter controls what wavelengths get through, of course. The filter therefore can be ground to compensate the focus point for those wavelengths. What the film records should not be a factor, since it can only record what gets through to it. Bob >> >> >>Compensation varies according to the film, as well as the lens. The >>focusing >>distance should be adjusted by 1/200 to 1/400 of the focal length of the >>lens, at infinity. Which fraction to use depends upon trial and error. > > Compensation should depend on the spectral response of the film. Those > such as HIE that are sensitive further into the IR region need more > compensation than films such as Konica 750 or Maco 820 that don't have as > wide a spectral response. The further the incoming 'light' is into the IR > region, the further behind the film plane the main bundle will be > focussed. > > Compensation also depends on the design of the lens; many modern lenses > have a much flatter spectral response and don't need as much compensation > or none at all into the near infrared, whereas the 1/200 compensation is > needed for older (60's or older) lenses using HIE. In any case, stopping > down to middle or small apertures is needed with HIE in any case as hardly > any lenses display severe aberrations at 850-900nm that can be brought > into line by stopping down. > > -- > * Henning J. Wulff > /|\ Wulff Photography & Design > /###\ mailto:henningw@archiphoto.com > |[ ]| http://www.archiphoto.com > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information >