a) shows a simple experiment using an aperture mask in a re-imaged aperture plane. b) and c) show diagrams of aperture masks which were placed in front of the secondary mirror of the Keck telescope by Peter Tuthill and collaborators. The solid black shapes represent the subapertures (holes in the mask). A projection of the layout of the Keck primary mirror segments is overlaid.
Aperture Masking Interferometry is a form of speckle interferometry, allowing diffraction limited imaging from ground based telescopes. This technique allows ground based telescopes to reach the maximum possible resolution, allowing ground-based telescopes with large diameters to produce far sharper images than the Hubble Space Telescope. The principle limitation of the technique is that it is limited to relatively bright astronomical objects. A mask is placed over the telescope which only allows light through a small number of holes. This array of holes acts as a miniture astronomical interferometer. The method was developed by John E. Baldwin and collaborators in the Cavendish Astrophysics Group. A secondary mirror (or secondary) is a second light gathering and focusing surface in a reflector telescope. ... The Mauna Kea Observatory, an institute of the University of Hawaii, is considered one of the most important land-based observatories in the world for its isolated, unobstructed views of space without interference from man-made light sources. ... The Mauna Kea Observatory, an institute of the University of Hawaii, is considered one of the most important land-based observatories in the world for its isolated, unobstructed views of space without interference from man-made light sources. ... Speckle interferometry is an image processing technique used in astronomy that can dramatically increase the resolution of ground-based telescopes. ... 50 cm refracting telescope at Nice Observatory. ... The Hubble Space Telescope (HST) is a telescope orbiting the Earth 370 miles above the atmosphere. ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... The Cavendish Astrophysics Group (formerly the Radio Astronomy Group) is based at the Cavendish Laboratory at Cambridge University. ...
In the aperture masking technique, the bispectral analysis (speckle masking) method is typically applied to data taken through masked apertures, where most of the aperture is blocked off and light can only pass through a series of small holes (subapertures). For simplicity these aperture masks are usually either placed in front of the secondary mirror (e.g. Tuthill et al. (2000)) or placed in a re-imaged aperture plane as shown in Figure 1.6a (e.g. Haniff et al. (1987); Young et al. (2000); Baldwin et al. (1986)). The masks are usually categorised either as non-redundant or partially redundant. Non-redundant masks consist of arrays of small holes where no two pairs of holes have the same separation vector (the same baseline - see aperture synthesis). Each pair of holes provides a set of fringes at a unique spatial frequency in the image plane. Partially redundant masks are usually designed to provide a compromise between minimising the redundancy of spacings and maximising both the throughput and the range of spatial frequencies investigated (Haniff & Buscher, 1992; Haniff et al. , 1989). Figures 1.6b and 1.6c show examples of aperture masks used in front of the secondary at the Keck telescope by Peter Tuthill and collaborators; Figure 1.6b is a non-redundant mask while Figure 1.6c is partially redundant. Although the signal-to-noise at high light level can be improved with aperture masks, the limiting magnitude cannot be significantly improved for photon-noise limited detectors (see Buscher & Haniff (1993)). A secondary mirror (or secondary) is a second light gathering and focusing surface in a reflector telescope. ... Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ...
Examples of high-resolution time-lapse movies produced with aperture masking (http://www.physics.usyd.edu.au/~gekko/wr104.html)
References
Peter Tuthill's PhD thesis on aperture masking (http://www.physics.usyd.edu.au/~gekko/papers/thesis.ps) as a postscript file which can be viewed in GSView (http://www.cs.wisc.edu/~ghost/gsview/)
Baldwin et al. (1986) (http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1986Natur.320..595B&db_key=AST)
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