= Coronagraph pupil-stop observing experiment
Schmid et al. tested the <Lyot stop> on sky using the close binary $\alpha$ Hydri with SPHERE/ZIMPOL at the Very Large Telescope. They kept the CLC-S-WF <coronagraphic focal plane mask>, the NB730 filter and pupil-stabilized imaging mode, and compared observations without a pupil stop and with stopB1_2. Each configuration used ten 8-second exposures. One camera imaged the <optical pupil> while the other simultaneously imaged the <focal plane>, connecting the blocked pupil features to the image improvement. https://doi.org/10.1051/0004-6361/201833620[Schmid et al., 2018, §4.2, figures 19–20 and table 10, test A]{ref}.
Bright rings occurred at the inner and outer pupil boundaries; the stop covered them and other unwanted features. To compare <point spread functions>, the authors multiplied the no-stop image by $0.68$, accounting for lost off-axis transmission. The companion's reported detection significance rose from $5.2$ to $9.7$. This demonstrates a useful gain despite lost companion <light>. It measures the complete stop, including obstruction, support-vane and faulty-actuator blockers; it does not isolate outer-rim clipping alone or establish a universal suppression factor. The figures here are independent toys, not reproductions of those observations. https://doi.org/10.1051/0004-6361/201833620[Schmid et al., 2018, §4.2 and table 10]{ref}.
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