ISIS is a high-efficiency, double-armed, medium-resolution (8 - 120 Å/mm) spectrograph, capable of long-slit work up to ~4' slit length. Use of dichroic slides permit simultaneous observing to be done in both the blue and red channels, which are optimised for their respective wavelength ranges. Spectropolarimetry and imaging polarimetry also available, as well as drift-scan mode for high-time resolution monitoring programmes. The default detectors are a large, thinned EEV42-type (4k*2k) device on the blue arm and a TEK CCD (1k*1k) on the red channel.

The EEV12 on ISIS blue arm

The CCD which is currently in use on the blue arm of ISIS is a thinned, blue sensitive EEV12; which is an array of 4096x2048 (13.5 micron) pixels . This is the default device for ISIS blue, and is ideally suited to this particular instrument. Our current policy is that this particular device will remain, almost permanently, at this focal station. We envisage many advantages with this decision, in particular

• Observers will have constant access to a superb, large format, blue sensitive device, which is probably the best suited device on the market for use on the ISIS blue channel
• The stability of having one device permanently mounted allows ING staff to monitor it's performance in detail, and over long periods. It also allows the whole system performance (WHT + ISIS + CCD) to be monitored on a consistent long term basis, producing an effective Quality Control mechanism. Staff resources are used more effectively to improve the stable system rather being wasted on quick fixes and work-arounds which have little long term benefit to ING users.

The MARCONI CCD on ISIS red arm

The default chip for ISIS red is now MARCONI2, and it is also our current policy to keep this particular MARCONI CCD permanently mounted and available for the reasons outlined above. In some unavoidable circumstances MARCONI2 may be changed for the TEK4 device (e.g. for Rapid Spectroscopic Mode).