Building a Newtonian Astrograph

1
Building aNewtonian Astrograph

• Curt Walker
• Presented October 2, 2009
• for the MARS Club

2
Topics Covered

• What is an astrograph?
• Building vs. Buying
• Design Tools
• Design Highlights
• Materials Components

• Fabricating Custom Parts
• Assembly
• First Light Focus Test
• First Photographic Results
• Finishing Touches

3
What is an astrograph ?

• An astrograph (astrographic camera) is a
  telescope designed for the sole purpose of
  astrophotography.
• Familiar forms of astrographs
• Schmidt Camera (different than Schmidt Newt)
• Short FL, low F-ratio APO refractors
• Ritchey-Chretien

4
Examples of currently mass-produced telescopes
that are (or could be) considered astrographs

• Meades Schmidt Newtonians

5
Examples of currently mass-produced telescopes
that are (or could be) considered astrographs

• Vixen R200SS

6
Examples of currently mass-produced telescopes
that are (or could be) considered astrographs

• Takahashi Epsilon 160 180

Epsilon 160
7
Examples of currently mass-produced telescopes
that are (or could be) considered astrographs

• Borgs Refractor Astrographic Systems

8
Examples of currently mass-produced telescopes
that are (or could be) considered astrographs

• TeleVues Nagler/Peztval APO Refractors

9
Examples of currently mass-produced telescopes
that are (or could be) considered astrographs

• Various Ritchey-Chretien OTAs

RC Optical Systems 16" f/8.4 CF OTA
RC Optical Systems 20" f/8.1 Carbon Truss
10
Buying vs. Rolling Your Own

• Reasons that influenced my decision to build
• Conversations with other ATMs
• Luxury of choosing each component to suit
  needs/wants
• Quality assurance (ha ha)
• No perfect matches with my needs/wants among
  commercially-made astrographs (all require
  upgrades)
• My compulsive need to build stuff.

11
Design Tools

• NEWT 2.5

12
Design Tools

• TurboCAD 14 Deluxe

13
Design Highlights

• .a telescope designed for the sole purpose of
  astrophotography.

• Needs Wants
• 8 aperture
• 1000mm focal length
• Classic newtonian
• Fine focusing control
• Imaging first, visual second
• Optical accessories
  (barlow or coma correction)
• Minimal vignetting

• Manifested in specs
• Thin or lightweight parabolic primary
• Motorized stepper focuser
• Spacings for camera focus (extenders may be
  required for visual)
• Spacings with room for optical accessories
• Fully illuminated imaging plane

14
Design Highlights

• Planning for a fully illuminated imager

• The focal plane is generally fully illuminated in
  the center, and gradually tapers off in
  brightness toward the edge.
• The 100 zone will have all of the brightness
  available from the primary mirror.
• The 75 zone is the area at the focal plane which
  is 3/4 illuminated by the primary mirror.

Source NEWT 2.5 Help Files
15
Design Highlights

• Planning for a fully illuminated imager

• Differing design principals for visual vs.
  imaging
• Visual
• The larger the eyepiece field lens, the larger
  areas of 100 and 75 illumination required.
• However, To see fine details in planetary images
  and faint nebulae alike, you need the maximum
  contrast possible.
• In a newtonian telescope, one of the biggest
  contrast killers is an oversized diagonal mirror.
• If possible, the diagonal minor axis should be
  kept under 20 of the diameter of the primary
  mirror.

Source NEWT 2.5 Help Files
16
Design Highlights

• Planning for a fully illuminated imager

• Differing design principals for visual vs.
  imaging
• Imaging
• To attain the brightest image possible and help
  avoid vignetting, the imaging plane should be as
  fully illuminated as possible.
• This requires substantially larger secondary
  mirrors than in similarly sized scopes intended
  for visual observing.
• Typically, a telescope optimized for imaging
• will not perform well for visual observing.

Source NEWT 2.5 Help Files
17
Design Highlights

• Planning for a fully illuminated imager

100
1.194
18
Design Highlights

• Planning for a fully illuminated imager

QHY8
100
APS-C (DSLR)
SBIG ST-2000XM
Orion StarShoot
19
Materials Components

• Telescope Tube Hastings Aluminum Pipe
• 10 OD, 0.064 wall
• Both ends rolled
• Heavy but relatively cheap and available
• Variety of finishes

20
Materials Components

• Spider Vane Protostar
• Straight 4-vane
• Built-in secondary offset
• Internal dew heater

• Secondary Mirror Protostar
• 2.60 minor axis
• ULS Quartz
• Interferogram says 1/14th

21
Materials Components

• Focuser Moonlight Crayford
• 3-point compression ring
• Hi-Res Stepper Motor
• Cercis Controller
• Supports 2 focusers
• Supports 2 temp probes and profiles

22
Materials Components

• Primary Royce Conical
• 8 F/5
• 3.5 lbs
• Very secure mounting (no epoxy necessary)
• Cools quickly

23
Fabrication of Custom Parts
24
Fabrication of Custom Parts
25
Fabrication of Custom Parts
26
Assembly
27
Assembly
28
Assembly
29
Assembly
30
First Light Focus Test
31
Assembly
32
First Photographic Results
M51 Whirlpool Galaxy 3x300
33
First Photographic Results
NGC5139 Omega Centauri 13x120
34
First Photographic Results
M8 Lagoon Nebula 12x300
35
Finishing Touches
36
Finishing Touches
37
Whats Next?

• Currently saving up for a complete imaging rig
• Mount.GM11? Mach1GTO???
• Switch to a self-guided monochrome imager
• (i.e. SBIG ST-2000XM or similar)
• Transition to MaximDL or CCDSoft for capture and
  processing

38
References Education

• The Dobsonian Handbook
• A Practical Manual for Building Large Aperture
  Telescopes
• By Kriege Berry
• TurboCAD 14 Deluxe Help Files online user forum
• NEWT 2.5 Help Files
• Bryan Greer of Protostar
• Bob Royce of R. F. Royce Precision Optical
  Components
• Daniel Mounsey of Woodland Hills Telescopes
• Fellow ATMs across the globe via Cloudy Nights
  ATM Forum

39
Thank You
Questions?