Primordial D/H

This is the blunt blue-end test. If the instrument cannot do serious work in the 310-400 nm regime at spectral resolution in excess of 48,000, an important piece of the high-resolution case evaporates.

Suggested seed figure: a deuterium / hydrogen absorption-line example from a metal-poor QSO sightline.

Why ZShooter

• The science wants blue sensitivity, high S/N, and stable wavelength calibration all at once.

• AO enhancement is welcome here, but the natural-seeing instrument still has grasp.

Current design pressure

This case keeps pressure on the blue channel, resolving power, and calibration rather than on response time. It is a strong argument against drifting too far down in resolving power.

Build-out notes

• Add one short observing-requirements block with target brightness and S/N regime.

• Keep the language disciplined: this page is about capability pull, not a fake finalized survey plan.