Determination of Spitzer Space Telescope focus from IRAC images without a focus slew

Details Determination of Spitzer Space Telescope focus from IRAC images without a focus slew Determination of Spitzer Space Telescope focus from IRAC images without a focus slew

Oct 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004spie.5487..186h&link_type=abstract

Optical, Infrared, and Millimeter Space Telescopes. Edited by Mather, John C. Proceedings of the SPIE, Volume 5487, pp. 186-2

Mathematics

2

Scientific paper

Prior to launch, the Spitzer Space Telescope (SST) secondary focus mechanism was set to a predicted desired in-orbit focus value. This predicted setting, determined from double-pass cold chamber measurements and calculated ground-to-orbit corrections, had an uncertainty greater than the required in-orbit focus accuracy. Because of concern about the potential for failure in a cryogenic mechanism affecting all Spitzer instruments, it was required that any focus correction be made in a set of moves directly from the initial to the desired setting. The task of determining the required focus moves fell to IRAC (Infrared Array Camera), the instrument most affected by and sensitive to defocus. To determine the focus directly from examining images at a fixed focus, we developed two methods, "Simfit" and "Focus Diversity" (W. F. Hoffmann, et. al.1). Simfit finds the focus by obtaining the best match between observed images and families of simulated images at a range of focus settings. Focus Diversity utilizes the focal plane curvature to find the best fit of the varied image blur over the focal plane to a model defocus curve. Observations of a single star at many field locations in each of the four IRAC bands were analyzed before and during the refocus activity. The resulting refocus moves brought the focus close to the specified requirement of within 0.3 mm from the desired IRAC optimum focus. This is less than a "Diffraction Focus Unit" (λx(f/2)) of 0.52 mm at the SST focus at the shortest IRAC band (3.58 microns). The improvement in focus is apparent in both the appearance and the calculated noise-pixels of star images.

Affiliated with

Also associated with

No associations

Rating

Determination of Spitzer Space Telescope focus from IRAC images without a focus slew does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Determination of Spitzer Space Telescope focus from IRAC images without a focus slew, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Determination of Spitzer Space Telescope focus from IRAC images without a focus slew will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1807054