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Re: Simplified Bris Sextant (calibration)
From: Bill B
Date: 2012 May 15, 14:41 -0400
From: Bill B
Date: 2012 May 15, 14:41 -0400
Are two crossed polarizing filters (with on other filters) dark enough to view the sun with the naked eye? I tested a Tiffen crossed with a Nikon, and they measured max 6.5 f reduction. The sun pack on my Astra is 11.5 f stops--32x reduction over the polarizers. Even with a 2-stop ND filter included, the sun image was still to bright to view with the naked eye IMHO. I am also concerned with pointing a camera at the sun for more than a second or two with 6.5 f-stop reduction. At some point in the lens barrel the sun's image is reduced to a point, that point being near the aperture-control leaves if memory serves. Like setting a leaf on fire with a magnifying glass, severe damage is possible. Bill B. On 5/15/2012 12:55 AM, Greg Rudzinski wrote: > "How did you attach a dark filter to it?" > > Two linear polarizers are held with fingers for shading. The degree of > shading can be adjusted for best contrast. > > "Can you look through polarizing filters > at the Sun?" > > Yes. My Cassens & Plath sextant is equipped with polarizer shades. See > attached image showing how to hold the filters and reflector. >