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HDS efficiency

Degradation of Reflectivity on the Image Rotators (2026.07)

Reflectivity on both the blue and red image rotators has degraded significantly, which is a serious concern.
Preliminary result indicates:

  • Reflectivity of the image Rotaor (blue) is about ∼20 % at 3200A.
  • For image rotaor (red), that is ∼25 % at 5900A.

This is NOT included in ETC. The exposure time needs to be increased by a factor of 2–2.5 relative to the ETC prediction. Please contact to the primary SA of HDS before proposal submision if you consider to employ image rotators in your program.

The following plot presents the total efficiency of HDS, including the atmosphere and telescope. This plot is also available in postscript format.

HDS Efficiency Plot

This plot presents the efficiencies of the image rotators and atmospheric dispersion corrector (ADC). It too is available in postscript format.

Image Rotators and ADC Efficiency Plot

The degradation of NsOpt image rotators (both red & blue) was found in September 2013 (by the efficiency measurement after the primary mirror re-coating). Please be careful to employ image rotators in your program. Now (1/28/2014), HDS-ETC is including this effect of degradation.
There are no apparent changes in efficiency of HDS itself and NsOpt ADC.

NsOpt Image Rotators Efficiency Degradation