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WILLIAMS COLLEGE ECLIPSE EXPEDITION
Newkirk Camera images obtained
March 29, 2006, in Kastellorizo, Greece.
The Williams College Eclipse Expedition was supported by
the NSF, the National Geographic Society, and NASA.
(More
about the Williams College Expedition)
Other eclipse images
1998 ,
1999 ,
2001 ,
2002 ,
2006
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All images on this
web server are subject to copyright. If you wish to re-use these
images, copyright credit should be shown by displaying the words:
"©2006 - Wendy Carlos &
Jonathan Kern - all rights reserved"
on each of the images shown.
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Updated
29 April, 2009
The Newkirk
camera that Jonathan Kern
designed and built to obtain these images uses a 4" quartz/fluorite
doublet of 60.25" f.l. fed by an 8" quartz coelostat. Below are
unprocessed exposures obtained through the radially symmetric, neutral
density filter located in the focal plane, which compensates for the steep
decline in coronal radiance with increasing distance. (The Newkirk filter*,
after Gordon Newkirk, former director of the
High Altitude
Observatory.) It is fabricated by
evaporating a metal film onto glass in a high vacuum. The basic
requirement of such a filter is that it compensate as accurately as
possible for the radial decrease in brightness as one goes away from the
limb of the sun in the film plane of the telescope. Thus, the transmission
should vary as the reciprocal of the function describing the K+F+sky
brightness. This calls for an optical density of 10 -3 at the
limb (10 f/stops, or a factor of 1000) decreasing very rapidly to a
density of near unity at 4 solar radii. (See
curve) The solar image at focus was .570" in diameter. The plate scale
is .0175"/ minute of arc, yielding a photographic field of 2.12 by 2.68
degrees on 120 format roll-film (image size 2.23" x 2.81") . The central
spot you see in each image is the calibration window, which remains
centered on the sun. Because there is perceptible motion of the moon with
respect to the sun, the NEWKIRK filter may appear decentered. It is not.
These images are also side-reversed, because of the single reflection
introduced by the coelostat mirror.
*Radial filter techniques have also been pioneered by Marius
Laffineur and Serge Koutchmy in France.
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