Celestron CPC DELUXE 1100 HD, Instruction Manual

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The Celestron EdgeHD 21
Appendix B:
TECHNICAL PROFILE OF THE EDGEHD
0.7× FOCAL REDUCER LENS
Perhaps the most useful accessory you can get for an EdgeHD
telescope is a focal reducer. Although the long focal length
is a great advantage in capturing detailed images of nebulae,
galaxies, and especially of planetary nebulae, it also means the
field of view is sometimes smaller than desirable. The relatively
slow focal ratio also means rather long exposure times. We
designed our 0.7× Focal Reducer to provide a field of view
1.4× larger in angular diameter, giving you twice the sky area
coverage and halving the exposure time required to reach a
given signal-to-noise ratio. If your passion is imaging large
deep-sky objects, imaging in H
α
, SII, and OIII narrowband,
capturing the faint reflection nebulae often found around
Barnard’s dark objects, or just cutting your exposure (and
guiding) times down, the focal reducer is a “must-have” item.
Back in the days of film astrophotography, focal reducers
came to be poorly regarded. Although they would shorten the
focal length, they also produced fuzzy star images, had bad
field curvature, and suffered from severe vignetting. But the
days of film and ersatz focal reducers are over. The modern
EdgeHD focal reducer is the product of optical engineering
and precision manufacturing on a par with the design and
production of wide- and ultra-wide-field eyepieces.
We designed three EdgeHD 0.7x focal reducers, each
specifically tailored to the EdgeHD 1400, 1100, and 800,
respectively. The 1400 and 1100 reducers contain five
precision optical elements, while the 800 contains four
elements. To attain a level of performance worthy of the
EdgeHD, the designs employ low-dispersion lanthanum
rare-earth glass to control both chromatic and geometric
aberrations. All optical surfaces are multi-layer anti-reflection
coated to maximize light transmission, provide high-contrast
images, and minimize image ghosting.
The matrix spot diagram shows that star images on-axis are
diffraction-limited in green light, while rays at all wavelengths
concentrated near the Airy disk. Even at the outer edge of the
42mm image circle, green and blue rays are clustered tightly,
while red shows only a weak flare.
Both physically and mechanically, the 0.7× Reducer Lens is
more than comparable to a top-of-the-line wide-field eyepiece.
The CNC-machined housing easily supports the full weight
of your CCD camera or digital SLR camera without sag or
movement. And for safe storage, each unit is provided with
threaded metal covers for both the front and the back.
FIGURE B1. The EdgeHD 0.7x Focal Reducer shortens the
focal ratio of the of the EdgeHD 1400, 1100 and 800 while
maintaining sharp images across the full field. This enables CCD
imagers to reach the same signal-to-noise ratio on extended
objects in half the exposure time, and brings even the faintest
deep-sky objects within the range of your high-end digital SLR
camera.
The EdgeHD 0.7× Focal Reducer