Telescope

Overview

The Telescope defines the entrance pupil geometry of the simulated instrument — shape, diameter, central obstruction, and optional spider arms. It is a required argument when constructing most other OOPAO classes (Atmosphere, DeformableMirror, Pyramid, etc.), because it carries the pupil definition, pixel scale, and AO loop sampling time.

Note

In the current version of OOPAO, the Source object is the primary carrier of the electromagnetic (EM) field and phase. Each source maintains its own independent OPD and EM field, which is what all relay() methods operate on. The Telescope.OPD property is retained for backward compatibility only and should not be relied upon in new code.

The propagation chain

Light propagation in OOPAO is driven by the __mul__ (*) operator, which is defined on Source and Asterism. Writing ngs * obj calls obj.relay(ngs) under the hood. Every core OOPAO class implements a relay() method that receives the source and operates directly on its EM field.

A full propagation chain is simply a sequence of * operations:

ngs * tel * wfs        # relay called on tel, then on wfs

When multiple sources are grouped in an Asterism, the same mechanics apply — __mul__ iterates relay() over each source independently, so every source accumulates its own EM field:

ast * tel * wfs        # relay called on tel and wfs for each source in ast

The ** operator resets the source EM field to its initial (unaberrated) state before starting the propagation. Use it to ensure a clean propagation from scratch:

ngs ** tel * wfs       # reset ngs EM field, then propagate through tel and wfs

Key concepts

• Pupil mask — binary (or user-supplied reflectivity) 2-D array defining the aperture geometry.

• OPD (backward compatibility) — 2-D optical path difference map in metres, still present on the Telescope but no longer the primary OPD carrier. New code should read OPD from the source object directly.

• relay() — the method every core class implements to act on a source’s EM field. Called automatically by the * operator; rarely called directly by users.

• samplingTime — AO loop period in seconds, used by the Atmosphere to advance phase screens.

Quick start

from OOPAO.Telescope import Telescope
from OOPAO.Source import Source

# Create a VLT-like 8-m telescope at 1 kHz
tel = Telescope(resolution=240, diameter=8.0, samplingTime=1e-3,
                centralObstruction=0.14)

# Add four spider vanes (angles in degrees, thickness in metres)
tel.apply_spiders(angle=[0, 90, 180, 270], thickness_spider=0.05)

# Propagate a source through the telescope and WFS
ngs = Source('H', magnitude=8)
ngs * tel * wfs

# Reset EM field and re-propagate cleanly
ngs ** tel * wfs

# Compute a PSF (zero-padding factor = 2)
tel.computePSF(zeroPaddingFactor=2)

# Print the current optical path
tel.print_optical_path()

API reference

class OOPAO.Telescope.Telescope(resolution, diameter, samplingTime=0.001, centralObstruction=0.0, fov=0.0, pupil=None, pupilReflectivity=1.0, display_optical_path=False)

Defines the entrance pupil of the telescope.

Parameters:

• resolution (int) – Number of pixels across the pupil diameter.

• diameter (float) – Physical diameter of the telescope in metres.

• samplingTime (float) – AO loop period in seconds (1 / loop_frequency). Used by the Atmosphere to advance phase screens. Default 0.001.

• centralObstruction (float) – Fractional diameter of the central obstruction (0–1). Default 0.0.

• fov (float) – Field of view in arcseconds. Required for off-axis multi-source simulations. Default 0.0.

• pupil (numpy.ndarray or None) – User-defined binary pupil mask (2-D array). Overrides the automatic circular mask. Default None.

• pupilReflectivity (float or numpy.ndarray) – Uniform reflectivity scalar or 2-D map matching the pupil. Default 1.0.

• display_optical_path (bool) – If True, prints the optical path each time light is propagated to a WFS. Default False.

Key properties

OPD: numpy.ndarray

2-D optical path difference map in metres. Retained for backward compatibility only — the authoritative OPD is stored on the Source object.

pupil: numpy.ndarray

Binary 2-D pupil mask (1 inside aperture, 0 outside).

pupilLogical: numpy.ndarray

1-D boolean index of valid (illuminated) pixels, used to vectorise operations over the pupil.

pixelArea: int

Number of illuminated pixels (pupil.sum()).

pixelSize: float

Physical size of one pixel in metres (diameter / resolution).

src: Source or Asterism

Reference to the last source (or asterism) propagated through this telescope.

PSF: numpy.ndarray

Last PSF computed by computePSF().

Methods

relay(src)

Core propagation method. Called automatically by src * tel. Applies the telescope pupil and OPD to the source EM field.

Parameters:

src (Source or Asterism) – Source or Asterism being propagated.

apply_spiders(angle, thickness_spider, offset_X=None, offset_Y=None)

Carve spider vanes into the pupil mask.

Parameters:

• angle (list[float]) – List of vane angles in degrees. Length determines the number of spiders.

• thickness_spider (float) – Vane width in metres.

• offset_X (list[float] or None) – Per-vane X offset in metres. Default None (no offset).

• offset_Y (list[float] or None) – Per-vane Y offset in metres. Default None (no offset).

computePSF(zeroPaddingFactor)

Compute the PSF as the squared modulus of the Fourier transform of the complex pupil field. Result stored in PSF.

Parameters:

zeroPaddingFactor (int) – Zero-padding factor applied before the FFT. A value of 2 yields Shannon-sampled PSFs.

resetOPD()

Set OPD to zero. Retained for backward compatibility.

print_optical_path()

Print the ordered list of optical elements the source has been propagated through.

Operator summary

Expression	Effect
ngs * tel	Call tel.relay(ngs); applies pupil to source EM field
ngs ** tel	Reset ngs EM field, then call tel.relay(ngs)
ast * tel	Call tel.relay(src) for each source in the asterism
tel + atm	Couple atmosphere; tel.OPD follows atm.OPD (legacy)
tel - atm	Decouple atmosphere (legacy)
ngs * tel * wfs	Full propagation chain: telescope then WFS