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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextants with Polarizing filters
From: Bill B
Date: 2006 Jan 26, 23:09 -0500
From: Bill B
Date: 2006 Jan 26, 23:09 -0500
> Actually "ortho" means vertical thus 90 degrees to the horizontal plane Wow, Through the (polarized) Looking Glass http://photography.about.com/library/glossary/bldef_ortho.htm "Definition: Orthochromatic films were first produced by Hermann Vogel in 1873 by adding small amounts of certain aniline based dyes to ordinary photo emulsions, work that was extended by others including J M Eder, who introduced the use of the red dye erythrosine in 1884. Early photographic materials were sensitive to blue light only, but ortho materials extended this to green in the middle of the visible region. Green is also the colour our eyes are most sensitive to, so this greatly improved the tonal rendition of photographs. Ortho materials can be handled using red safelights, and are commonly used for special black and white films for darkroom use - such as lith film." Off topic, but how does that "ortho" film relate to right angles? Alice?