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: Meade’s 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: Borg’s Refractor Astrographic Systems

8. Examples of currently mass-produced telescopes that are (or could be) considered astrographs: TeleVue’s 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. 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

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?