IQ-R3¶

Focus/alignment procedure keeps all parts of the science array within 9 microns RMS of best focal plane. [Confirm "Focus" element of IQ budget in Table 2 after TO-2; DECam TO-6 covers focus change between passbands; TOM-13 gives commandability accuracy] To be tested over full HA/Dec range of Survey. Also to be checked once per observable night during SV and at least initial observations. [This is a test of the F/A system used to set hexapod.]

This requirement applies to the focus servo loop only.

Prerequisites¶

• Same as for IQ-R1
• Focus loop servo code in SISPI is installed and can be activated
• Nominal LUT table installed in SISPI
• NOMAD star selection code in SISPI is operating. (Backup - activate the star-finder code in Donut.)
• Night with changing temperatures.

Procedure¶

• Point (possibly open-loop) to a star field near zenith. Take a succession of 80 second exposures with the focus loop operating for at least 30 minutes.
• Repeat at TBD additional pointings of the telescope away from zenith
• Compute RMS of the servo-loop error signal.

Verdict¶

RMS for each pointing must be <= 9 microns.

Consequences¶

Determine RMS contribution to image size of actual focus loop performance. Compare with results achieve from IQ-R4. If R4 is still satisfied, assign excess FHWM contribution to contingency.