Changes

The "Instrument Selector" is essentially a new fold mirror that has been installed in the "acquisition boxes" of both SpUpNIC and HiPPO<ref>''22 Feb 2024: the implementation of the fold mirror in HiPPo's acquisition box has not been completed at time of writing</ref> that allows the observer to switch between two instruments: a "primary" and a "secondary" instrument where the primary instrument is either SpUpNIC or HiPPo and the secondary instrument is always a new SHOC system, [https://topswiki.saao.ac.za/index.php/SHOCnWonder SHOCnWonder]. In other words, a SHOC an imaging camera is from now on permanently available always mounted on the 74-inch1.9m, alongside either the spectrograph or the polarimeter, and the fold mirror can be positioned to use either primary or secondary instrument at any time.

Figure 1 shows how the new SHOC system is mounted to the side of SpUpNIC's acquisition box. The new fold mirror that acts as the "Instrument Selector" instrument selector is shown in the top panel and actuates IN/OUT of the science beam above the "guider guide mirror". The new SHOC system replaces the old guider XY slide box that use to migrate between SpUpNIC and HiPPo. The new SHOC system is incorporated into a newly designed off-axis "pick-off" style guider system that can accommodate a filter wheel unit and SHOC camera behind the guider. The new SHOC system It also has a focal reducer built in providing just over double the FoV-width compared to the the old system (2.7'&thinsp;&times;&thinsp;2.7' for the new system vs. 1.3'&thinsp;&times;&thinsp;1.3' for the old setup).

[[File:Instrument_selector.png|left|thumb|600px|Figure1: Instrument Selector Concept and new SHOC system mounted to the side of SpUpNIC's "acquisition box"]]

To select between the primary instrument and SHOC, a user can actuate the fold mirror in/out of the beam to direct the science beam towards the desired instrument (see Figure 2 below that indicates the button on TCS that actuates the fold mirror). When the fold mirror is IN beam and the guider's XY stages are "centred" then the guider guide camera also functions as a "target acquisition" camera for SpUpNIC/HiPPo, similar to the old system. Also as in the old system, the guider guide camera can patrol the area of the large annulas annulus mirror to acquire an appropriate guide star.