Previous: Exposure timing
Previous Page: Exposure timing
Next Page: TAURUS commands

Field of view

When TAURUS is used in imaging mode, the field of view is limited by the following factors:

  1. The field cutoff of the collimator, equal to 9 arcmin.

  2. Filters placed in the focal plane may further limit the field of view. The scale at the input focal plane is 4.51 arcsec mm-1 for TAURUS-2. Thus, for example, a filter with a diameter of 75 mm would limit the field to 5.6 arcmin. This constraint can be avoided by using filters in the pupil plane. However, using filters in the collimated beam leads to an increased risk of ghost images, and in the case of the smaller filters may cause vignetting.

  3. The size of the detector. The scale at the detector focal plane is 23.25 arcsec mm-1 for TAURUS-2 with the f/2.1 camera and 12.40 arcsec mm-1 for TAURUS-2 with the f/4 camera. Thus, for example, the EEV3 CCD, whose size is 27.9x25.7mm, will provide a field of 5.8x5.3 arcmin when used with the f/4 camera.

  4. Optical quality. The f/4 camera is designed to give high spatial resolution at the expense of field. The quality of the images therefore degrades somewhat with field radius (see section ?). This may place a limit on the fieldsize useable for a particular project.

When TAURUS-2 is used as a Fabry-Perot interferometer, the field may be further limited by the following factors:

  1. The field of view of TAURUS-2 is not limited in the conventional way by the Jacquinot criterion (Journal of the Optical Society of America, vol 44, p761, 1954). At high resolutions, the field will however be limited by the width of the interference fringes. The wavelength change across a detector pixel increase with both the distance from the field centre and with the resolution, so there exists an off-axis angle beyond which the wavelength change across a single pixel is greater than the spectral resolution. For a pixel size of p micron and a resolving power R, the off-axis angle in arcmin at which this results in a a degradation of resolution by a factor of sqrt(2) is given by:

    k = 12.5 for TAURUS-2 with the f/2.1 camera
    * k = 23.5 for TAURUS-2 with the f/4 camera

  2. The total size of a datacube must not exceed the amount of memory available in the Detector Memory System (48 Mbyte as of 17/5/91).

Thu Apr 7 00:29:52 BST 1994