On the Figuring of Specula

Rue, Warren De La

doi:10.1093/mnras/13.2.44

Cited by 3 publications

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“…48 That much was known at the time, and the astrophotographer Warren de la Rue candidly admitted: "I am … free to confess that they [the refractors] defined a fixed star much more satisfactorily than my best mirrors." 49 Refracting telescopes do not suffer as readily from the large amount of scattered light known to have characterized specula and, indeed, most of the trustworthy observations of the Sirius companion in the nineteenth century were made with such instruments.…”

Section: (B) Modern Considerations On Astronomical Image Qualitymentioning

confidence: 99%

Why Was the Companion of Sirius Not Seen Prior to 1862?

Wesemaël

Racine

2008

Journal for the History of Astronomy

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Section: (B) Modern Considerations On Astronomical Image Qualitymentioning

confidence: 99%

Why Was the Companion of Sirius Not Seen Prior to 1862?

Wesemaël

Racine

2008

Journal for the History of Astronomy

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“…Both these well-known makers worked their mirrors upon polishing machines of their own design (54,55), but again tell us nothing about planes.…”

Section: Warren De La Rue and Thomas Grubbmentioning

confidence: 99%

The production of a plane surface, as illustrated by specula from some early Newtonian telescopes

1983

Notes Rec. R. Soc. Lond.

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THE construction of accurate paraboloidal mirrors for reflecting telescopes has been the subject of much attention from physicists, practical opticians, and historians of science. However, the paraboloidal primary must be combined with a secondary mirror to give any form of working telescope other than the Herschelian design, and the quality of this secondary is every bit as important to the definition of the final image. In the Newtonian reflector the secondary mirror takes the form of a plane surface of elliptical outline. Historical specula therefore provide a practical record of attempts to achieve a perfectly flat solid surface— an undertaking which has often proved more difficult than making mirrors of a curved figure. Plane surfaces were subsequently required in many optical instruments besides telescopes, such as prisms and diffraction gratings. Then, in the early decades of the nineteenth century, another field of application was created when Maudslay, Whitworth and others realized the need for accurately flat surfaces in precision engineering and toolmaking. To test their products and ensure interchangeability they had to produce plane surfaces upon cast iron ‘surface plates’ and the hardened steel anvils of screw micrometers.

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Two Centuries of Image Quality Estimates from Double-Star Data

Racine¹,

Wesemaël²

2008

PUBL ASTRON SOC PAC

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ABSTRACT. We examine the historical evolution of the image quality delivered by astronomical telescopes since the days of William Herschel. This is done by analyzing double-star discovery data from nine celebrated observers who used 12 telescopes at 11 sites. Complementary information is derived from errors in the separation measurements of the Sirius system between 1862 and 1960. The best delivered image quality steadily improved with time, from a full width at half maximum intensity of 5″ in 1780 to 0.5″ in 1970. This appears to have resulted largely from increasingly better optics. Selection effects and limitations that have affected these double-star surveys are briefly discussed, as is the driving role toward telescope improvement played historically by the study of double stars.

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On the Figuring of Specula

Cited by 3 publications

References 0 publications

Why Was the Companion of Sirius Not Seen Prior to 1862?

Why Was the Companion of Sirius Not Seen Prior to 1862?

The production of a plane surface, as illustrated by specula from some early Newtonian telescopes

Two Centuries of Image Quality Estimates from Double-Star Data

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