pith. machine review for the scientific record. sign in

arxiv: 2605.02687 · v1 · submitted 2026-05-04 · 🌌 astro-ph.IM · astro-ph.SR

Recognition: 2 theorem links

Operating the Fabry-P\'erot systems of the European Solar Telescope in multi-aperture mode

B. Lindberg, D. Kiselman, G.B. Scharmer, H. Socas-Navarro, J. de la Cruz Rodr\'iguez, J. Leenaarts, M.G. L\"ofdahl, M. Rempel

Authors on Pith no claims yet

Pith reviewed 2026-05-08 17:48 UTC · model grok-4.3

classification 🌌 astro-ph.IM astro-ph.SR
keywords European Solar Telescopemulti-aperture modeFabry-Perotimage restorationsolar spectropolarimetryhigh-altitude seeingadaptive optics
0
0 comments X

The pith

Segmenting the European Solar Telescope aperture into six 1.4 m subapertures reduces high-altitude seeing errors for better restored images before MCAO is available.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper proposes operating the European Solar Telescope in a multi-aperture mode by segmenting its 4.2 m aperture into six 1.4 m subapertures using simple modifications to the Fabry-Perot camera lenses. This approach lowers the wavefront errors from high-altitude atmospheric turbulence, making it easier for post-processing techniques to restore high-quality images. The result is more stable and sustained high-resolution data, especially useful for time sequences of spectropolarimetric observations during the telescope's initial years. Simulations confirm that this low-cost, switchable mode can significantly boost science output without affecting the main optics or waiting for the full MCAO system.

Core claim

By optically segmenting the 4.2 m aperture into six 1.4 m subapertures, the RMS wavefront errors from high altitude seeing are pushed down to levels that post-processing image restoration can more reliably correct. This significantly improves image quality and provides the sustained stable high image quality needed for obtaining time sequences of spectropolarimetric data. The mode is implemented with low-cost modifications to the three Fabry-Perot systems covering 380-860 nm, allowing quick switching and flexible operation based on wavelength-dependent seeing conditions.

What carries the argument

Optical segmentation of the telescope aperture into six smaller subapertures through modifications to the Fabry-Perot camera lenses, which reduces the effective aperture diameter to mitigate high-altitude seeing effects.

If this is right

  • Improved reliability of post-processing image restoration for high-altitude seeing.
  • Sustained high image quality for spectropolarimetric time series.
  • Independent and quick switching for each of the three FPI systems to optimize for different wavelengths.
  • No impact on primary or secondary optics or the FPI systems themselves.
  • Potential for more and better science data in the pre-MCAO period.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The multi-aperture mode could provide valuable data for validating image restoration algorithms that will later be used with MCAO.
  • It offers a way to start high-resolution solar observations earlier, potentially accelerating discoveries in solar physics.
  • Similar aperture segmentation strategies might be applicable to other large ground-based telescopes during their commissioning phases.

Load-bearing premise

Reducing the effective aperture diameter will lower the RMS wavefront errors from high-altitude seeing to levels that post-processing image restoration can reliably correct without introducing significant new aberrations or light-loss penalties.

What would settle it

Direct side-by-side comparison of restored images from full-aperture and multi-aperture observations under identical seeing conditions would show if the expected reduction in wavefront errors and improvement in quality actually occurs.

Figures

Figures reproduced from arXiv: 2605.02687 by B. Lindberg, D. Kiselman, G.B. Scharmer, H. Socas-Navarro, J. de la Cruz Rodr\'iguez, J. Leenaarts, M.G. L\"ofdahl, M. Rempel.

Figure 1
Figure 1. Figure 1: Schematic layout of the EST aperture (large circle) with its 1.1 m central obscuration (small circle), and the proposed seven (six useful) 1.4 m hexagonal subapertures. The numbering of the subaper￾tures shown is used in Tables 2, B.1, and B.2 discussing layout and pre￾dicted performance. The x and y coordinate system shown, normalised to the diameter of a sub-aperture, is used to define the center coordin… view at source ↗
Figure 2
Figure 2. Figure 2: The short-exposure PSFs of 1 m, 1.4 m, and 4.2 m apertures, normalised to unity at their peaks. Note that the FWHM (indicated with vertical gray lines) of the seeing degraded PSFs is larger for the 4.2 m aperture than for the smaller apertures when r0 is 0.35 m or smaller. This provides the desired flexibility in optimising EST for each FPI system independently. The actual implementation of the multi-apert… view at source ↗
Figure 4
Figure 4. Figure 4: The “true” 12′′ .2×12′′ .2 image that the artificial “observed” im￾ages are based on. This is based on a a simulation snapshot calculated by Rempel (2020). From this, we calculated a synthetic image as seen through the 0.4 nm FWHM 630.2 nm prefilter of CRISP2, centered on a pair of magnetically sensitive FeI lines. 1′′ tickmarks. Asplund et al. (2009) abundances and non-grey radiative transfer with 12 opac… view at source ↗
Figure 3
Figure 3. Figure 3: Left: MTFs of 1.0 m, 1.4 m, and 4.2 m apertures. Right: the corresponding MTFs normalised to that of a 4.2 m aperture. The vertical gray lines mark the diffraction limits of the 1.0 m and 1.4 m apertures. The spatial frequency scale is in units of the limiting spatial frequency of a 4.2 m telescope. MTF of a diffraction limited 4.2 m aperture, emphasising that the seeing degraded MTFs with r0 = 0.35 m or s… view at source ↗
Figure 5
Figure 5. Figure 5: The angular averages are calculated after taking the logarithm. view at source ↗
Figure 7
Figure 7. Figure 7: Part of the FOV of the truth image in view at source ↗
Figure 8
Figure 8. Figure 8: shows power spectra obtained from the images de￾graded by seeing and added noise as described in the Figure. The power spectrum of the ground truth image is shown as a dotted curve for comparison. We emphasise, that only the top two plots, corresponding to a burst of 50 images with excep￾tionally low noise (1.0 × 10−4 ) shows clear evidence of power that goes beyond the diffraction limited limit of the 1.4… view at source ↗
Figure 10
Figure 10. Figure 10: MFBD reconstructed images from the 1.4 m (left) and 4.2 m (right) apertures with outstanding seeing corresponding to r0 = 1 m, ex￾ceptional low noise (1.0×10−4 ), and using 100 Karhunen–Loeve modes for the MFBD reconstruction. extent relies on post-processing and image reconstruction tech￾niques, and is ultimately limited by noise. We have during sev￾eral decades developed and repeatedly improved PD and M… view at source ↗
Figure 11
Figure 11. Figure 11: MFBD reconstructed images with 50 Karhunen–Loeve modes from the 1.4 m and the 4.2 m apertures, with seeing corresponding to r0 = 0.35 m and 0.20 m, and different levels of noise. and output Strehl values is good with the 4.2 m aperture. How￾ever, in more realistic seeing conditions, the correlation is poor. In contrast, the correlation is tight between input and output Strehl values for all r0 values with… view at source ↗
Figure 14
Figure 14. Figure 14: Comparisons of input and output (from MFBD processing) Strehl values with 4.2 m and 1.4 m apertures. Low noise corresponds to 1.0 × 10−4 and high noise to 3.0 × 10−3 with 50 frames. 0.0 0.1 0.2 0.3 0.4 0.5 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.0 0.1 0.2 0.3 0.4 0.5 Distance (") 0.00 0.01 0.02 0.03 0.04 0.05 0.06 PSF input PSF model PSF D: 4.2 m r0 : 100 cm Low noise 0.0 0.1 0.2 0.3 0.4 0.5 0.005 0.010 0.01… view at source ↗
Figure 12
Figure 12. Figure 12: MFBD reconstructed images 100 Karhunen–Loeve modes from the 1.4 m and the 4.2 m apertures, with seeing corresponding to r0 = 0.20 m, and different levels of noise. 0.01 0.10 10−8 10−7 10−6 10−5 10−4 10−3 10−2 0.01 0.10 Normalised frequency 10−8 10−7 10−6 10−5 10−4 10−3 10−2 Power 1.0 m 1.4 m 4.2 m True r0 = 35 cm Low noise 0.01 0.10 10−8 10−7 10−6 10−5 10−4 10−3 10−2 0.01 0.10 Normalised frequency 10−8 10… view at source ↗
Figure 15
Figure 15. Figure 15: Comparisons of input and estimated (from MFBD processing) PSFs for a 4.2 m aperture, and 1.4 m aperture. Of particular interest here are the pupil images at P1 and P2, which for the EST FPI systems has diameters in the range 7– 8 mm. For EST-V the pupil diameter is 6.8 mm both on the input and output sides. The lens L2 re-images the pupil plane P1 onto infinity at the location of the etalons (F2), and the… view at source ↗
Figure 16
Figure 16. Figure 16: Comparisons of input and estimated (from MFBD processing) squared MTFs of PSFs for a 4.2 m aperture and 1.4 m aperture. the pupil pass the etalons with the same angle of incidence, but rays from different parts of the pupil pass the etalons with differ￾ent angles of incidence. Because of the telecentric configuration with the pupil at infinity, this variation of the angle of incidence across the pupil is … view at source ↗
Figure 17
Figure 17. Figure 17: Layout of EST-V (overall length 4.5–4.7 m, FPI clear aperture diameter 180 mm). Symbols used: F1-F3 are focal planes, L1-L4 lenses, P1-P2 pupil planes, PBS polarising beam splitter. P2 is the pupil stop with the 2.3 mm prisms, L4 is the camera lens. The vertical scale has been expanded 2× for clarity. Adopted from Scharmer et al. (2026) view at source ↗
Figure 18
Figure 18. Figure 18: 3D visualisation of the 2.3 mm prisms, located at the pupil stop P2. The purpose of the prisms is to deflect and separate the seven possible (six useful) subimages at the focal plane of the detector view at source ↗
Figure 20
Figure 20. Figure 20: Spot diagrams for the multi-aperture modification of FPI-V for seven wavelengths in the range 610–670 nm, at various distances from the center of the 1′ FOV. The lowest Strehl value is 0.95 configurations of the three FPI designs developed for EST. At the top of each Table, we give the setup and performance of an ideal system with infinite F-ratio and that of the default single￾aperture FPI system. We the… view at source ↗
Figure 21
Figure 21. Figure 21: The FPI transmission profiles for EST-V in its default FPI configuration with full aperture, the multi-aperture configuration without HR etalon tilt, and the multi-aperture configuration with HR etalon tilt. Profiles from all six subapertures are plotted for the two multi-aperture configurations. For details, see view at source ↗
read the original abstract

We discuss how to optimise the science output of the European Solar Telescope (EST), when used without the wide-field compensation for high-altitude seeing that the EST multi conjugate adaptive optics (MCAO) will offer. This will be the mode of operating EST during its first year(s). Without MCAO, the spatial resolution of a much smaller telescope could surpass that of EST. We therefore propose to operate EST in multi-aperture mode, by optically segmenting the 4.2 m aperture into six 1.4 m subapertures, until MCAO is operational. Operating at smaller aperture diameter pushes down the root mean square wavefront errors from the high altitude seeing to levels that can more reliably be compensated for in restored images using post processing methods. This will significantly improve image quality. In particular, the multi-aperture mode will provide the sustained stable high image quality needed for obtaining time sequences of spectropolarimetric data. The multi-aperture mode is implemented with low-cost modifications of the camera lenses of the three Fabry-Perot systems that will be used to cover the wavelength range 380--860~nm. Switching between the full-aperture and multi-aperture modes can be done quickly and independently for the three FPI systems. This allows flexible optimisation of EST, taking into account that the seeing is much better at long wavelengths than at short wavelengths, without any impact on the EST primary or secondary optical systems or on the actual FPI systems. The multi-aperture addition to EST provides a powerful and flexible option that has the potential of significantly improving the quality and amount of its science data before MCAO is operational. In this publication, we perform simulations and image reconstructions of simulated data to demonstrate the benefits of the multi-aperture option, and provide a simple optical design to demonstrate its feasibility.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper proposes operating the European Solar Telescope (EST) in multi-aperture mode during its initial years without MCAO by optically segmenting the 4.2 m primary into six 1.4 m sub-apertures via low-cost modifications to the camera lenses of the three Fabry-Pérot systems (380–860 nm). This reduces high-altitude seeing RMS wavefront errors to levels more reliably correctable by post-processing image restoration, enabling sustained high-quality time sequences of spectropolarimetric data. The authors present a simple optical design for quick switching between modes and demonstrate benefits through simulations and image reconstructions of simulated data.

Significance. If the quantitative performance claims hold, the multi-aperture mode would provide a practical, reversible enhancement to early EST science output by improving image stability and quality for spectropolarimetry without affecting the primary optics or FPI systems. The approach leverages standard seeing models and restoration techniques, offering a flexible interim solution until MCAO is commissioned.

major comments (2)
  1. [§4] §4 (Simulations and image reconstructions): The restored images and claimed improvement in image quality are presented without quantitative injection of wavefront errors, differential piston/tip-tilt, or throughput losses from the added segmentation optics and masks in the FPI camera lenses. The central claim that sub-aperture operation reduces high-altitude seeing RMS to reliably correctable levels (and thereby enables stable spectropolarimetric time series) requires an explicit error budget showing that added aberrations remain below ~0.1 wave RMS and losses below ~15 %; absent this, the performance gain does not follow from the presented simulations.
  2. [§3] §3 (Optical design): The feasibility demonstration describes the lens modifications but provides no ray-trace results, pupil segmentation error analysis, or measured/estimated light-loss figures for the six-sub-aperture configuration. These quantities are load-bearing for the assertion that the mode can be implemented without degrading SNR or introducing new aberrations that would offset the seeing benefit.
minor comments (2)
  1. [Abstract] The abstract states that simulations were performed but reports no numerical metrics (e.g., Strehl ratios, RMS residuals, or comparison baselines between full-aperture and multi-aperture cases); adding these to the abstract and §4 would improve clarity.
  2. [§2] Notation for sub-aperture diameter and effective focal length after segmentation is introduced without an explicit equation or diagram reference; a short definition in §2 would aid readers.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments. We address each major point below and have revised the manuscript to incorporate the requested quantitative details.

read point-by-point responses

  1. Referee: §4 (Simulations and image reconstructions): The restored images and claimed improvement in image quality are presented without quantitative injection of wavefront errors, differential piston/tip-tilt, or throughput losses from the added segmentation optics and masks in the FPI camera lenses. The central claim that sub-aperture operation reduces high-altitude seeing RMS to reliably correctable levels (and thereby enables stable spectropolarimetric time series) requires an explicit error budget showing that added aberrations remain below ~0.1 wave RMS and losses below ~15 %; absent this, the performance gain does not follow from the presented simulations.

    Authors: We agree that an explicit error budget is needed to fully support the claims. In the revised manuscript we have added a dedicated error-budget paragraph in §4. Using typical manufacturing tolerances for the mask and lens modifications, added aberrations are estimated at <0.07 waves RMS. Throughput losses from the masks are quantified at ~12 %. Differential piston/tip-tilt between sub-apertures is discussed as correctable by existing AO or standard post-processing calibration, consistent with current solar observing practice. The core simulation result (reduced high-altitude seeing) remains valid and is now placed in this quantitative context. revision: yes

  2. Referee: §3 (Optical design): The feasibility demonstration describes the lens modifications but provides no ray-trace results, pupil segmentation error analysis, or measured/estimated light-loss figures for the six-sub-aperture configuration. These quantities are load-bearing for the assertion that the mode can be implemented without degrading SNR or introducing new aberrations that would offset the seeing benefit.

    Authors: We have expanded §3 with results from a simple ray-trace model of the modified camera lenses. The model shows that the added segmentation optics introduce <0.05 waves RMS of aberration beyond the intended sub-aperture geometry. Pupil segmentation mismatch is <0.5 % in area. Light losses are estimated at 10–15 % (wavelength-dependent) from the opaque masks; these figures are now stated explicitly together with the ray-trace plots. The additions confirm that the optical changes remain compatible with the claimed performance gain. revision: yes

Circularity Check

0 steps flagged

No significant circularity; proposal grounded in standard seeing models and forward simulations

full rationale

The paper's derivation chain rests on established physical scaling of high-altitude seeing wavefront errors with aperture diameter and the known performance of post-processing image restoration techniques. Simulations of restored images are forward-modelled from external atmospheric and optical assumptions rather than fitted to the target outcome. The optical design is presented as a low-cost feasibility sketch without invoking self-citation chains, uniqueness theorems, or ansatzes that loop back to the claimed benefits. No equations reduce by construction to parameters defined by the result, and the central claim about sustained image quality for spectropolarimetry follows from independent models of RMS error reduction. This is the common honest case of a self-contained proposal without circular steps.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The work is an engineering proposal that draws on established solar-telescope seeing statistics and image-reconstruction methods; it introduces no new physical constants, entities, or ad-hoc axioms beyond standard domain assumptions.

free parameters (1)
  • subaperture diameter
    Chosen as 1.4 m to divide the 4.2 m primary into six equal segments for practical hexagonal packing.
axioms (1)
  • domain assumption High-altitude seeing produces the dominant uncorrectable wavefront errors for large-aperture solar telescopes without MCAO
    Invoked to justify why smaller subapertures improve post-processing restorability.

pith-pipeline@v0.9.0 · 5680 in / 1364 out tokens · 71864 ms · 2026-05-08T17:48:17.855369+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

23 extracted references · 1 canonical work pages

  1. [1]

    J., & Scott , P

    Asplund , M., Grevesse , N., Sauval , A. J., & Scott , P. 2009, , 47, 481

    2009

  2. [2]

    2025, EST Management Plan, Tech

    Barreto Cabrera , M., Nu\ nez Cagigal , M., Socas Navarro , H., et al. 2025, EST Management Plan, Tech. Rep. EST-0100-EPO-PLN-0826, EST Foundation, La Laguna, Tenerife, Spain

    2025

  3. [3]

    Fried , D. L. 1966, Journal of the Optical Society of America (1917-1983), 56, 1372

    1966

  4. [4]

    2025, EST Operations Plan, Tech

    Gonzalez Manrique , S. 2025, EST Operations Plan, Tech. Rep. EST-1200-EPO-PLN-0749, EST Foundation, La Laguna, Tenerife, Spain

    2025

  5. [5]

    Irwin , A. W. 2012, FreeEOS: Equation of State for stellar interiors calculations , Astrophysics Source Code Library, record ascl:1211.002

    2012

  6. [6]

    L \"o fdahl , M. G. 2002, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 4792, Image Reconstruction from Incomplete Data, ed. P. J. Bones , M. A. Fiddy , & R. P. Millane , 146--155

    2002

  7. [7]

    G., Henriques , V

    L \"o fdahl , M. G., Henriques , V. M. J., & Kiselman , D. 2011, , 533, A82

    2011

  8. [8]

    G., Hillberg , T., de la Cruz Rodr \' guez , J., et al

    L \"o fdahl , M. G., Hillberg , T., de la Cruz Rodr \' guez , J., et al. 2021, , 653, A68

    2021

  9. [9]

    L \"o fdahl , M. G. & Scharmer , G. B. 1994, , 107, 243

    1994

  10. [10]

    & Feller , A

    Nagaraju , K. & Feller , A. 2012, , 51, 7953

    2012

  11. [11]

    R., et al

    Quintero Noda , C., Schlichenmaier , R., Bellot Rubio , L. R., et al. 2022, , 666, A21

    2022

  12. [12]

    2020, , 894, 140

    Rempel , M. 2020, , 894, 140

    2020

  13. [13]

    R., Warner , M., Keil , S

    Rimmele , T. R., Warner , M., Keil , S. L., et al. 2020, , 295, 172

    2020

  14. [14]

    2004, Adaptive Optics in Astronomy

    Roddier , F. 2004, Adaptive Optics in Astronomy

    2004

  15. [15]

    Scharmer , G. B. 2006, , 447, 1111

    2006

  16. [16]

    B., de la Cruz Rodr \' guez , J., Leenaarts , J., et al

    Scharmer , G. B., de la Cruz Rodr \' guez , J., Leenaarts , J., et al. 2026, , 705, A55

    2026

  17. [17]

    Scharmer , G. B. & Lindberg , B. 2025, arXiv e-prints, arXiv:2505.21053

    work page arXiv 2025

  18. [18]

    B., L \"o fdahl , M

    Scharmer , G. B., L \"o fdahl , M. G., Sliepen , G., & de la Cruz Rodr \' guez , J. 2019, , 626, A55

    2019

  19. [19]

    B., L \"o fdahl , M

    Scharmer , G. B., L \"o fdahl , M. G., van Werkhoven , T. I. M., & de la Cruz Rodr \' guez , J. 2010, , 521, A68+

    2010

  20. [20]

    B., Sliepen , G., Sinquin , J

    Scharmer , G. B., Sliepen , G., Sinquin , J. C., et al. 2024, , 685, A32

    2024

  21. [21]

    2010, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol

    Soltau , D., Berkefeld , T., S \'a nchez Capuchino , J., et al. 2010, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 7736, Adaptive Optics Systems II, ed. B. L. Ellerbroek , M. Hart , N. Hubin , & P. L. Wizinowich , 77360U

    2010

  22. [22]

    van Noort , M., Rouppe Van Der Voort , L., & L \"o fdahl , M. G. 2005, , 228, 191

    2005

  23. [23]

    R., Martinez Pillet , V., et al

    Warner , M., Rimmele , T. R., Martinez Pillet , V., et al. 2018, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 10700, Ground-based and Airborne Telescopes VII, 107000V

    2018