Prime Focus Camera

The most notable feature of the DCT is its large prime focus assembly (PFA), which includes the prime focus corrector optics and the CCD camera (PFC) consisting of 40 e2v CCD44-82 2K x 4K CCD's; this combination yields a very wide 2-degree field-of-view. A Phase-2 design study was completed at Goodrich Corporation in 2005 that reduced the  projected cost significantly through changes in several of the original  requirements: 

  • relaxation of the image quality requirement to that based  on 10% degradation of median seeing rather than 1st quartile average  seeing;
  • no U-band image quality requirement (but U-band capability was preserved);
  • modification of the ADC to a tilt/decenter style on element  L4;
  • and repackaging of the PFA without a secondary mirror.
PFA_2006

The new PFA  design uses fused silica in 4/5 elements and standard glass LLF6 in element 4, and utilizes spherical surfaces on all but two: an ellipsoid  on L3 and an asphere on L5. The image quality requirements, including  recovery of the partial U-band, are exceeded over the full 2o field to 75o zenith distance.

The figure at left shows the new conceptual PFA  structure.  From left to right, the main components are the cable wrap,  the prime focus CCD camera, the shutter and the filter changing mechanism, the ADC assembly, and the prime focus corrector optics.

The figure below shows the layout of the new conceptual PFA structure, indicating the telescope interface and main mechanized component.
topend_schem_2006

The wide field of view of the PFC, illustrated below in the image of Andromeda, will be essential for KBO and NEO surveys. It will also be a  valuable asset for several proposed astrophysics programs.
Andromeda05

The current PFA design for the Discovery Channel Telescope is described and published in the 2006 Proceedings of SPIE and can be viewed HERE. The original concept design study for the PFA was published in the 2004 SPIE Proceedings and can be viewed HERE.

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