Optical and mechanical details

Some data

Total tube length (focuser retracted)	148 cm
Weight	5,3 kg
Eyepiece connector	standard 50.2 mm + 31.8 mm adapter
Mount adapter	"Vixen"-type dovetail, length 30 cm

Instrument prototype mark I, during testing.

The focuser has a 2 inches eyepiece holder + a 1.25 inches adapter. On the rim of this adapter, a standard 42x0.75 mm (T2) male thread is additionally present, very common among photographic accessories. From the rim of the 1.25 adapter to the focal plane, the distance is ~90 mm. One should note that this is a fixed distance by design, i.e. it cannot be varied by acting on the focuser knobs.

Optical design

The design of the Cytherograph (please note the parts that we provide to the observers) is the same as the Lyot coronagraph with :

• a main lens (doublet) called O1 (Skywatcher BK 1021 EQ3-2, D: 102mm F: 1000mm)
• an occulting disk with an occulting cone in front of it. In the Cytherograph, the occulting disk is displaced in order to get the solar limb on the optical axis.
• a field lens called O2 ( [NT48-184] (1.0'' Dia F/4.0 Molded Acrylic Aspheric Lens, VIS Coated))
• a diaphragm ( [NT32-622] )
• a O3 lens ( [NT47-643] Achromatic Lens 25mm Dia. x 150mm FL, VIS 0 Coating)
• a filter (interferential filter, bandwidth < 10nm)
• a O3' lens ( [NT47-649] Achromatic Lens 25mm Dia. x 300mm FL, VIS 0 Coating
• the focal plane (CCD,...)

Our Cytherograph is based on a standard 1000mm focal length refractor. The resulting focal length is enlarged to 2514 mm by the combination of O2, O3 and O3' lenses.

The pixel scale is 0.416 arcsec/pix (for 5µm pixels), so that the 58" arcsec Venus disc lay on 140 pixels.

Optical ZEMAX model

Coro4.zmx

Mechanical design of the Cytherograph

*Important note this design (3D model) is the prototype's one, based on a Meade 90/1000 refractor different from the Skywatcher refractor that will be used for the series Cytherographs.
The mechanical solutions adopted for the prototype should be the same for the series (in particular, the distances in the coronagraphic part from the occulting disk to the focal plane are good) , but the final mechanical design must be adapted to the new refractor.

2D and 3D drafts (in the same VariCAD file) : CoroVenus+Protus4_Meade90_F.dwb

VariCAD Viewer software (free) : Allows to view the drafts in 2D and 3D.

LINUX

• varicad2012-view-en_1.01_amd64.deb
• varicad2012-view-en_1.01_i386.deb
• VariCAD_View_2012-en-1.01-1.i586.rpm
• VariCAD_View_2012-en-1.01-1.x86_64.rpm

WINDOWS

• VariCADViewer2012-1.01-EN.exe

Basic use of VariCAD :

• Shift + left click : zooming + or -
• CRTL + left click : panning XY in 2D and 3D
• Shift + CTRL + left click : rotating XYZ in 3D

VariCAD is quite easy to use, but for other functions (measuring distances, dimensions), here is the excellent manual.

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