Celestron EDGEHD, Manual

Page 1: ...A FLEXIBLE IMAGING PLATFORM AT AN AFFORDABLE PRICE Superior flat field coma free imaging by the Celestron Engineering Team Ver 04 2013 For release in April 2013 ...

Page 2: ...tives Our classic SCT has three optical components a spherical primary mirror a spherical secondary mirror and a corrector plate with a polynomial curve As every amateur telescope maker and professional optician knows a sphere is the most desirable optical figure In polishing a lens or mirror the work piece moves over a lap made of optical pitch that slowly conforms to the glass surface Geometrica...

Page 3: ...EdgeHD series consists of four aplanatic telescopes with 8 9 25 11 14 inch apertures The optical design of each instrument has been individually optimized to provide a flat coma free focal plane Each EdgeHD optic produces sharp images to the edge of the view with minimal vignetting EdgeHD Series ...

Page 4: ...e wanted to produce equally fine imaging telescopes at a more consumer friendly price As we ve already noted our most important design goal for the new telescope was to eliminate coma and field curvature over a field of view large enough to accommodate a top of the line full frame digital SLR camera or larger astronomical CCD camera This meant setting the field of view at 42 mm in diameter Of cour...

Page 5: ...s compare the center to edge optical performance of the classic SCT coma free SCT and EdgeHD The EdgeHD clearly outperforms the other optical systems The classic SCT shows prominent coma The coma free SCT is indeed free of coma but field curvature causes its off axis images to become diffuse and out of focus In comparison the EdgeHD s spot pattern is tight concentrated and remains small from on ax...

Page 6: ...ree SCT you can see that off axis images in the classic SCT images are strongly affected by coma As expected the images in the coma free design do not show the characteristic comatic flare but off axis they do become quite enlarged This is the result of field curvature Figure 3 illustrates how field curvature affects off axis images In an imaging telescope we expect on axis and off axis rays to fo...

Page 7: ...ly on the baffle tube causing the image to shift In the classic SCT the shift does not significantly affect on axis image quality However in the EdgeHD off axis images could be affected Because the baffle tube carries the sub aperture corrector inside and the primary mirror on the outside we manufacture it to an extremely tight diametric tolerance The tube that supports the primary was redesigned ...

Page 8: ...ed careful testing guarantee that the telescope will not only perform well for high power planetary viewing but will also cover a wide angle field for superb edge to edge imaging Nevertheless we don t take this on faith both before and after assembly we test and tune each set of optics Celestron s founder Tom Johnson invented the breakthrough process used to make Celestron s corrector plates Over ...

Page 9: ... of low expansion borosilicate glass Like the primaries the secondaries are edged and centered then ground and polished The secondary is a convex mirror so during manufacture it is tested against a concave precision reference matchplate to check both its radius of curvature and figure The secondary mirrors are also brought to the QA Interferometry Lab where the radius and irregularity of each mirr...

Page 10: ...he Pelican Nebula testifies to the EdgeHD s ability to focus clean neat round star images from center to edge The telescope was a 14 inch EdgeHD on a CGE Pro Mount the CCD camera was an Apogee U16m The mage above shows a 21 5 29 8mm section cropped from the original 36 8mm square image EDGEHD S CLOSE UP ON THE PELICAN NEBULA ...

Page 11: ... conduct the FAT on an optical test bench in a specially constructed temperature controlled room Figure 12 Rather than use laser light for this test we use white light so that the FAT reproduces the same conditions an observer would experience while viewing or photographing the night sky To avoid placing any heat sources in the optical path the light for our artificial star is carried to the focus...

Page 12: ... 1 inch visual back and this accepts a 1 inch Star Diagonal that will accept any standard 1 inch eyepiece The EdgeHD 925 1100 and 1400 feature a heavy duty flange with a 3 290 16 tpi threaded flange This oversize flange allows you to attach heavy CCD cameras and digital SLR cameras For visual observing use the adapter plate supplied with each telescope to attach the Visual Back The 2 inch Diagonal...

Page 13: ...Not only are they strong but they also hold your camera perfectly square to the light path To mount a high performance video camera add the T Adapter plus a T to C adapter Like the T mount system the C mount system is an industry standard It uses 1 32 tpi threads with a back focus distance of17 5mm For consumer video systems such as electronic eyepieces planetary cameras and webcams that attach to...

Page 14: ...ging at the ƒ 10 or ƒ 11 focus The linear field of view is still 42mm diameter but the angular field is 43 larger and exposure times drop by a factor of two For super fast super wide imaging the EdgeHD telescope series supports Starizona s Hyperstar lens Mounted on the corrector plate in place of the secondary mirror the Hyperstar provides an ƒ 1 9 focal ratio on the EdgeHD 1400 and ƒ 2 0 or ƒ 2 1...

Page 15: ...bout optical design fabrication and testing 11 REFERENCES DeVany Arthur S Master Optical Techniques John Wiley and Sons New York 1981 Fischer Robert E Biljana Tadic Galeb and Paul R Yoder Optical System Design McGraw Hill New York 2008 Geary Joseph M Introduction to Lens Design Willmann Bell Richmond 2002 Malacara Daniel ed Optical Shop Testing John Wiley and Sons New York 1978 Rutten Harrie and M...

Page 16: ...gure A1 the left column shows the Airy disk for a telescope with a central obstruction of 34 Because the light in the Airy disk is concentrated into a smaller area in the center capturing all of the image detail in a planetary or lunar image requires using a 2x or 3x Barlow lens to further enlarge the Airy disk Unfortunately ideal conditions are fleeting During a typical CCD exposure atmospheric t...

Page 17: ... C digital SLR camera relative illumination falls to 84 at the extreme corners of the image Although for bright subjects this minor falloff would pass unnoticed for imaging faint objects we recommend making and applying flat field images for the best results For CCD imaging we always recommend making flat field images Portability and affordability are the hallmarks of the EdgeHD 800 Although the 8...

Page 18: ...nicely balanced On a night of average seeing stars will display a FWHM of 23µm comparable in size to the spot pattern at the very edge of a 42mm field Relative illumination in the EdgeHD 925 is excellent The central 12mm is completely free of vignetting while field edges receive 90 relative illumination For most imaging applications flat fielding would be optional For full field imaging on a tight...

Page 19: ...PS C digital SLR camera flats are unnecessary For monochrome imaging with an astronomical CCD camera we always recommend making flat field images On nights when the seeing achieves 1 5 arcseconds FWHM star images shrink to 18µm at the focal plane On such nights the EdgeHD 1100 delivers fine images over a 30mm image circle and well defined stars over the full 42mm field The EdgeHD 1100 is a serious...

Page 20: ...it to display its full resolution only on the finest nights Relative illumination is 100 across the central 16mm and falls slowly to 83 in the extreme corners of a full frame 35mm image sensor We have seen excellent results when the 14 inch EdgeHD is used with a KAF 16803 CCD camera over a 50mm circle The EdgeHD 1400 is a massive telescope well suited to a backyard observatory or well planned away...

Page 21: ...ield 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 aberratio...

Page 22: ...onstrate that the focal reducer s star images are even smaller than those of the telescopes For observers who wish to pursue faint nebulae in RGB or in narrowband the 0 7 Focal Reducer is a valuable accessory that halves the necessary exposure time with no sacrifice in resolution or image quality 5 75 inches 146 05 0 5 mm EdgeHD 1100 and 1400 Large T Adapter T Ring Adapter Digital SLR Large T Adap...

Page 23: ...from one side to the other star images are sharp crisp and round As you process your image fine details in the target object reveal themselves Star clouds delicate dust lanes subtle HII regions it s all there credit to your skill and the design of your EdgeHD telescope The image shown here is a single monochrome 10 minute exposure taken with an Apogee U16 camera KAF 16803 CCD chip and a Celestron ...

Page 24: ...The Celestron EdgeHD 2013 by Celestron All rights reserved Torrance CA 90503 U S A www celestron com ...