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Altair Field Lens



The Altair field lens is designed to provide better Strehl and sharper image quality at large distances from the guide star, essentially reducing the anisoplanatism of the system.

The first tests of a prototype field lens were taken in July and August 2005 and showed large improvements in AO correction, especially at large distances from the guide star. Initial results were so dramatic that it was immediately offered for use. The final field lens was installed in 2006B. This document summarizes what PIs need to know to work with the field lens.

Important notes starting in 2007A

PIs planning to use Altair should do the following:

Field Lens Overview

The field lens is a convex lens designed to conjugate Altair to the ground level, rather than at high altitude. The overall benefit of this re-conjugation of the system is to provide better Strehl and sharper image quality at large distances from the guide star, essentially reducing the anisoplanatism of the system. The field lens is designed to be "optional" as it may be placed into the beam or out of the beam with little overhead.

Initial testing of the field lens has shown that it improves correction even at very far distances from the guidestar, up to 25 arcseconds (the limit of the field lens coverage). Without the field lens, high quality correction is limited to about 5 to 7 arcseconds from the guide star. Use of the field lens should allow a factor 20 to 30 improvement in sky area available to Altair.

Disclaimer

As of this writing, the final field lens has just been installed. Afull battery of tests have not been done to completely characterize the new field lens, however, a prototype lens has been in use since 2005. The information listed on this page is taken from tests undertaken on two nights only of the prototype lens. It is likely that under different seeing conditions, the improvements seen with the field lens may not be as dramatic as those shown here. As more information is learned about the characteristics of the current prototype field lens, updates will be made to this webpage.

Reasons NOT to Use the Field Lens

Reasons to Use the Field Lens

Images

The following images of M33 visually demonstrate the performance increase with the use of the field lens. These were taken under good seeing conditions (August 2005). The width of the strip corresponds to about 45 arcseconds on the sky. The guide star is the nucleus of the galaxy, left of center.

Field lens OUT, K-band K out

Field lens IN, K-band K in

Field lens OUT, H-band H out

Field lens IN, H-band H in

Field lens OUT, J-band
(not available)

Field lens IN, J-band J in

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Page Compiled by Chad Trujillo. Last update Feb 22, 2007.