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Image artifacts - Internal reflections
Light reflecting inside the telescope optics, and diffracting off edges within
the telescopes, can produce some interesting effects. Consider this series of
images showing the planet Venus leaving the field of view of the HI1-B
telescope between Janary 26-31, 2009. As Venus approaches the edge of the
field-of-view, a ring shape is seen apparently coming out of the planet. This
is caused by reflections of the bright planet off of the camera barrel. (If
you look closely at the full-field version of the January 26, 2009 image above,
you'll see a large, faint bubble on the left side of the image, which is also
an internal reflection of Venus.) The ring grows progressively larger as time
goes by. On January 31, a horizontal streak appears near the position where
Venus disappeared. This latter effect is caused by diffraction off of the
optical baffles. Click here for a
more detailed explanation
|The planets Mercury (left) and Venus (right) as seen in the
HI1-B telescope on January 26, 2009. Click on the images to see full-sized
||Venus leaving field-of-view January 27, 2009. Ring caused by
reflection off of camera surfaces.
|Venus out of field-of-view, but still reflecting off camera
surfaces, January 28, 2009.
||Diffraction of Venus off baffle edges, January 31, 2009
Here's an image from the HI2-B telescope which shows a number of interesting
internal reflections. The brightest object in the field is our own planet
Earth, which is responsible for all the reflection effects. Also visible is
the Moon, and the planet Mars. A similar event is described on
|Internal reflections of the planet Earth, as seen in the HI2-B
telescope on May 5, 2007. Also visible are the Moon, and the planet Mars.
Click on the image to see the full-sized version.
Below is another example of internal reflections in the STEREO telescopes, this
time from the COR2 telescope, taken when the extremely bright planet Venus was
passing through the field of view. Circled is a faint reflection of the
planet. Clicking on the image will bring up a movie showing the reflection
entering the field from the right, and then slowly fading away. Also visible
in the movie are some debris events.
|Internal reflection of the planet Venus, as seen in the COR2-A
telescope on May 2, 2010. Click on the image to see a movie of the
reflection (3 MB).
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Last Revised: Tuesday, 03-Jul-2012 14:50:07 EDT
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