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Building a Newtonian Astrograph. Curt Walker Presented October 2, 2009 for the MARS Club. Topics Covered. What is an astrograph? Building vs. Buying Design Tools Design Highlights Materials & Components. Fabricating Custom Parts Assembly First Light & Focus Test

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building a newtonian astrograph

Building aNewtonian Astrograph

Curt Walker

Presented October 2, 2009

for the MARS Club

topics covered
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
what is an astrograph
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
examples of currently mass produced telescopes that are or could be considered astrographs
Examples of currently mass-produced telescopes that are (or could be) considered astrographs:

Meade’s Schmidt Newtonians

examples of currently mass produced telescopes that are or could be considered astrographs5
Examples of currently mass-produced telescopes that are (or could be) considered astrographs:

Vixen R200SS

examples of currently mass produced telescopes that are or could be considered astrographs6
Examples of currently mass-produced telescopes that are (or could be) considered astrographs:

Takahashi Epsilon 160 & 180

Epsilon 160

examples of currently mass produced telescopes that are or could be considered astrographs7
Examples of currently mass-produced telescopes that are (or could be) considered astrographs:

Borg’s Refractor Astrographic Systems

examples of currently mass produced telescopes that are or could be considered astrographs8
Examples of currently mass-produced telescopes that are (or could be) considered astrographs:

TeleVue’s Nagler/Peztval APO Refractors

examples of currently mass produced telescopes that are or could be considered astrographs9
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

buying vs rolling your own
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.
design tools
Design Tools

NEWT 2.5

design tools12
Design Tools

TurboCAD 14 Deluxe

design highlights
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
design highlights14
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

design highlights15
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

design highlights16
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

design highlights17
Design Highlights

Planning for a fully illuminated imager:

100%

1.194”

design highlights18
Design Highlights

Planning for a fully illuminated imager:

QHY8

100%

APS-C

(DSLR)

SBIG

ST-2000XM

Orion

StarShoot

materials components
Materials & Components
  • Telescope Tube – Hastings Aluminum Pipe
  • 10” OD, 0.064” wall
  • Both ends ‘rolled’
  • Heavy but relatively cheap and available
  • Variety of finishes
materials components20
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
materials components21
Materials & Components
  • Focuser – Moonlight Crayford
  • 3-point compression ring
  • Hi-Res Stepper Motor
  • Cercis Controller
  • Supports 2 focusers
  • Supports 2 temp probes and profiles
materials components22
Materials & Components
  • Primary – Royce Conical
  • 8” F/5
  • 3.5 lbs
  • Very secure mounting (no epoxy necessary)
  • Cools quickly
first photographic results
First Photographic Results

M51 – Whirlpool Galaxy

3x300

first photographic results33
First Photographic Results

NGC5139 – Omega Centauri

13x120

first photographic results34
First Photographic Results

M8 – Lagoon Nebula

12x300

what s next
What’s 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
references education
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
thank you
Thank You

Questions?

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