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NOTE: for instructions to focus the telescope during observations, go to software. This page is about focussing an individual camera after maintenance.

Focusing

This procedure is applied when focusing the cameras by using an artificial light source. By using the cameras browser (DOTgui) you record images for the different channels. Open the script named “FocusTest”. This script establishes the focus calibration steps (in mm).

• Set the exposure time: 4.9 s and interval: 5 s.

• Ensure the artificial lights source is on.

• Start measurement (normal images and flats are then taken).

• Turn the artificial light source off.

• Take a burst of 10 dark images.

Note: If you accidentally take more burst than the specified ones, it is rather better to delete the new created files and start again the process. There must be 17 generated files (15 + flat + dark) in every camera data directory. List the files ordering them according to the time stamps:

ls - t

• Working in jeff:

  mkdir /home/dot/Fokus_201?.??.?? (Create a directory the files linking to the /camera/NAME)

• Copy IDL routines from an old run into the new directory

  cp /home/dot/Fokus_2008.09.09/*.pro /home/dot/Fokus_201?.??.??/

• Make a link pointing to the raw images.

  ln -s /camera/* /home/dot/Fokus_201?.??.??/

• Run the IDL routine to generate the flatfielded burst of images for every channel. This routine creates FITS files named Focus*.fits, each of them corresponding to a data cube for every channel. Run the IDL routine to generate flats (FITS fomats):

  .r genflats

• Run the IDL routine that computes the contrast (RMS) measurements in the different patches over the images conforming the data cube. The higher the contrast value, the better the focus determination is. First you have to edit the program foc3.pro. Select the channel you want to operate with (0 for first channel and so on). Choose the number of patches (in x and y) that will be computed.

  nx=[camera1,camera2,camera3,camera4,camera5] (Change only the one for the ny=[camera1,camera2,camera3,camera4,camera5] camera you are working with)

Run the IDL routine to display the images and calculate the focus position:

.r foc3

Select the lower left and upper right corners for the whole patches, make sure you do it according to the numbers of patches chosen. The programs computes the focus and generates a postscript file with the results.

• Visualize the results

  evince idl.ps

Write down the computed Focus position value.