SKY-WATCHER ED SPECIFICATIONS
WHAT
IS ED?
Extra-low Dispersion glass allows the optical designer to virtually eliminate
chromatic aberration (false color fringing around bright objects), which results
in higher resolution and superior contrast in the images.
SKY-WATCHER FLUORITE ED APOCHROMATIC REFRACTORS
Skywatcher Pro-Series ED refractors are built with a two element air spaced
objective. The second element is made of the highest grade ED fluorite glass
called FPL-53. This premium glass choice is a basic warranty for virtually no
false color and for high contrast. The high standard set in material choice is
also set in production. No efforts are spared to reach optimal optical quality:
Our best opticians give each objective a hand pitch polishing finishing touch.
This dedication to perfection together with aspheric shaping technology are the
best ways to reach a very good wavefront* which means virtually no aberrations
and textbook star images. The quality of each ED Pro Series objective is
monitored by means of a Ronchi* test and a star** test.
Ronchigrams for lens aberrations
*
The essential function of a telescope is gathering starlight without
"disturbing" it. This means changing the path of the lightwaves
without altering the lightwave itself. Lightwaves all together are referred to
as a wavefront.
Alterations in this wavefront caused by the optics should be avoided. A
wavefront analysis by Ronchi test will show an absence of wavefront alterations
if the black and white lines (interference pattern) are perfectly straight and
parallel.
** The star test proves the ability of the optics to reproduce a pinpoint light source (star) as a pinpoint image. Concentric light circles will surround the pinpoint light dot. These increasingly faint light circles are unavoidable due to diffraction but being well concentric around the central light dot they are a warranty for good optical alignment of the lenses.
Achromatic Refractor ED Refractor
Secondary
spectrum achromatic refractor
ED
refractors secondary spectrum