Royal Museums Greenwich. "Non-achromatic telescope". http://collections.rmg.co.uk/collections/objects/43768.html. [Accessed: June 2016].
Public Notes:
Objective Notes 2016:
Not removable (cell tacked in). Measured curvature starside. Comparison with measured focal length leads to conclusion that the objective is asymmetrically biconvex, with eyeside flatter than starside. Ronchi test shows very well-made lens. Aperture is best estimate.
Museum Description:
"This crudely made non-achromatic telescope has three draw tubes. The barrel and two of the draw tubes are made of leather, while the smallest draw tube is made of iron. The other fittings are of leather and horn and include a tapering sun shade fixed to the end of the barrel. The eyepiece has a metal cap. This is believed to be an early example, although the lenses are quite large for a 17th century telescope" (Royal Museums Greenwich).
physical lengths in mm: 345, 317, 313, 247
starside to extension mark:
star-side tube diameter: 68
eye-side tube diameter: 57
ring diameter:
Drawtube notes:
Main tube of wood. Draws 1 and 2 pasteboard. Draw 3 sheet metal. No clear extension marks. Eyepiece lenses now off-axis, but rough image is visible with objective focal length 610 mm and effective eyepiece at 80 for magnification of ca. 8x. Last (eyeside) third of main tube has an inner tube, which decreases the inner diameter of the main tube to meet the outer diameter of Draw 1. (Potential explanation: This functions as a stop on the objective - nearly half (in diameter) of a light beam incident on the objective is blocked by this lip and does not pass into Draw 1.) Inside tube begins at ca. 190 mm away from light source of the 610 mm focal length. Opening of this inner tube: 41 mm at eyeside vs. 47 mm at objective aperture. Metal tube of innermost tube brings to mind the metal tube telescopes at Skokloster and in Kassel, which likely date from the 1660s and 1670s.
Objective Data
CA curvature (diopters):
CB curvature (diopters):
PD lens power (diopters):
fD focal length (mm):
t thickness (mm):
free aperture (mm):
full aperture (mm):
nD refractive index:
ν Abbe No.:
Lens 1
523.36
837.77
1.64
610.00
60.00
60.00
Eyepieces
Notes:
3 biconvex lenses (now off-axis). Eye lens beveled, field lens grozed. Eye lens pressure fit within zigzag metal-foil holder.
Dioptrice is made possible by the generous
support of the National Science Foundation, the National
Endowment for the Humanities, the Program in the History and
Philosophy of Science at the University of Notre Dame, and the Adler Planetarium & Astronomy Museum.
