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Дата изменения: Wed Jan 30 03:28:30 2002
Дата индексирования: Tue Oct 2 09:55:36 2012
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Out-Of-Focus (OOF) Holography

New data sets, etc, are available from the "new" holography page: please use this link

This page will eventually be absorbed into the above page and disappear!
Out-of-focus holography is one of the methods used to measure the deformation of a telescope surface away from its ideal (or design) shape.
Prof. R. Hills, Dr. J. Richer and me have been working on a OOF holography system primarily aimed at the SCUBA/JCMT set-up, but deliberately designed to be extensible enough to be used on a wide range of telescopes. Our preliminary results are shown below.

 

October 2001 data of Mars from the JCMT/SCUBA, using the improved algorithms

The seeing was good enough to be able to reduce both 850 and 450 micron data.
  aperture calculated from 850 micron data
  aperture calculated from 450 micron data
  Data, model and residuals for 850 micron data
  Data, model and residuals for 450 micron data

JCMT SCUBA data

These maps were taken in March 2001. The maps and the model fits are shown in following files:
 -1mm defocus data and model maps
 -0.5mm defocus data and model maps
 infocus data and model maps
 0.5mm defocus data and mode map
 1mm defocus data and model maps

The map of surface errors (shown as phase errors in radians) and the map of calcualated surface illumination is shown in the following plot:
 Phase and illumination map

NEW: more detailed phase and illumination map
  Detailed Phase and illumination map

Older Rx A scanning data

These maps were taken at a wavelength of 1.3mm, and were produced by scanning the telescope across the sky. Only single differentiation (i.e. just the chopping motion) is needed, and the chop throw is fairly large.

An interesting feature of these data sets are the effects introduced by chopping of the secondary mirror: besides moving the two images from the centre of the map, it also introduces a coma term which flips sign between the two images. The size of the differential coma term is proportional to the chop throw, so these largo chop throw maps should make this effect significant. When we fitted for these effects we found good agreement between calculated and measured values for the differential coma term.

Mars data

Bellow are the plots of actual measured data and the best model fits for each defocus settings.
 -2mm defocus data and model maps
  infocus data and model maps
  +2mm defocus data and model maps

The map of surface errors (shown as phase errors in radians) and the map of calcualated surface illumination is shown in the following plot:
 Phase and illumination map

Venus data


 -1.7mm defocus data and model maps
 -1mm defocus data and model maps
 infocus data and model maps
 1mm defocus data and mode map
 1.7mm defocus data and model maps

The fitted and original maps are shown in the following plot:
 Phase and illumination map

These fits can be compared to fits by the old holography software.

Other materials

My write up on this topic (out of date): oof.ps (1MB)
A short users manual for the OOF Holography package: manual.ps (70KB)