Table 1
Input parameters for the seven dual FPI systems discussed.
| Parameter/FPI system | CRISP | CRISPm | CRISP2 | CHROMIS | EST-B | EST-V | EST-R |
|---|---|---|---|---|---|---|---|
| Telescope | SST | SST | SST | SST | EST | EST | EST |
| FPI system status | Obsolete | Operational | In progress | Operational | Proposal | Proposal | Proposal |
| Telescope diameter (m) | 0.98 | 0.98 | 0.98 | 0.98 | 4.2 | 4.2 | 4.2 |
| Input focal ratio | 46 | 46 | 46 | 46 | 50 | 50 | 50 |
| FOV diameter (arc min) | Max | Max | Max | Max | 1.0 | 1.0 | 1.0 |
| Etalon clear aperture (mm) | 75 | 75 | 98 | 75 | Min | Min | Min |
| Camera pixel size (μm) | 16 | 6.5 | 6.5 | 5.48 | 5-12 | 6-12 | 6-12 |
| Wavelength range (nm) | 500-860 | 500-860 | 520-860 | 390-500 | 380-500 | 500-680 | 680-1000 |
| Reference wavelength(s) (nm) | 630 | 630 | 630 | 390 | 380 396 | 500 630 | 680 854 |
| Required rms cavity error (nm) | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| Target Strehl intensity (%) | 90 | 90 | 90 | 90 | 90 | 90 | 90 |
| Spectral FWHM at ref. wavel. (pm) | 6 | 6 | 7 | 8 | 7.9 | 6.3 | 11 |
| Peak transmission (%) | 90 | 90 | 90 | 90 | 90 | 90 | 90 |
| Parasitic light level (%) | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| Prefilter type | 2-cavity | 2-cavity | 2-cavity | 2-cavity | 2-cavity | 2-cavity | 2-cavity |
Notes. CRISP and CRISPm are identical except for their camera lenses. The three designs of the FPI systems for EST were proposed by (Scharmer & Lindberg 2025), based on requirements decided by the EST Science Advisory Group, but have not been reviewed by the EST project. The first reference wavelength for EST FPI systems refers to the requirement on Strehl, the second to the requirement on spectral resolution. The Strehl intensities required refer to a combination of apodisation effects and optical design limitations.
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