ESO Faint Object Spectrograph and Camera
EFOSC2 Focusing Tests

Technical time 17/1/2002

Aim: To test the new Focus Prism template written by Emilio Barrios, and to compare its performance with the other focusing methods (Focus Sequence and Focus Wedge).

Telescope pointed to spectrophotometric standard LTT1788 near the zenith. Three sets of tests were made:

The DIMM seeing and the serrurier temperature were noted down during each focus procedure. Furthermore the seeing is measured from the best focused image. The results are shown below:

Best encoder values obtained using different focusing methods:

Focus Sequence dsee Focus Wedge dsee Focus Prism dsee Method Temp
1933 0.06" 1951 0.24" 1936 -0.23" Started from 50 Encoder units below 12.1 -- 11.8
1939 -0.30" 1953 0.34" 1947 -0.15" Started from 50 Encoder units above 11.7
1941 (see graph below) -0.06" 1949 -0.09" 1943 -0.15" Started near best focus 11.6 -- 11.5
1938 -0.04" Last test. 11.5
mean dsee= -0.09" mean dsee= 0.16" mean dsee= -0.18"
mean=1938 mean=1951 mean=1942

dsee = measured seeing - DIMM seeing. Positive values means that the telescope seeing is worse than DIMM seeing

Below shows the plot from the focus sequence in the 3rd set of test:

It can be seen that:

Preliminary conclusions

Send comments to : ls-spectro

Last modified: Fri Jan 18 03:15:27 SAT 2002

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