There are a number of factors which limit the field of view of TAURUS-2:

An absolute limit to the field size obtainable with TAURUS-2 is the field cutoff of the collimator, which is 9 arcmin.

When order sorting filters (see ) are placed in the focal plane, they may further limit the field of view. The scale at the input focal plane is 4.51 arcsec/mm for TAURUS-2. The diameters of all the order sorting filters available for TAURUS-2 are listed in Appendix . 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.

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 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

The field size will also be limited by the amount of memory available to store the TAURUS datacube during the data acquisition process. is organised means that the field size must be an integer power of 2. The amount of memory available is currently 32 Mbyte, which taken together with the need to sample the spectral dimension properly, means that the largest datacube possible has dimensions of 25625660.

Tue Aug 15 16:42:46 BST 1995