Optical Configurations for Astrophotography

Imaging the Sky 2012 Intel HF-3 Auditorium, Hillsboro, OR

May 5-6, 2012 Richard Berry

In this talk… I describe the designs commonly used by

amateurs, present a brief analysis of the performance that can be expected from a well-made instrument of each type, and discuss the

weaknesses and strengths of each design.

I do not discuss the merits of different manufacturers, but instead about the properties

of optical designs based on inescapable physical and optical limitations of their design.

Refracting Astrographs

•  Achromatic Refractor •  Apochromatic Refractor •  Apochromatic Refractor w/ Field Corrector •  Petzval Apochromatic Astrograph

Achromatic Refractor

Achromatic Refractor Color Curve

Achromatic Refractor Spot Matrix

Apochromatic Triplet 150mm aperture, ƒ/8

Apochromatic Triplet 150mm aperture, ƒ/8

Achromat versus Apochromat

Apochromatic Triplet w/ Field Corrector

150mm aperture, ƒ/8

Apochromatic Triplet w/ Field Corrector 150mm aperture, ƒ/8

Apochromatic Petzval Astrograph 100mm aperture, ƒ/5.5

Apochromatic Petzval Astrograph 100mm aperture, ƒ/5.5, at best visual focus

Apochromatic Petzval Astrograph 100mm aperture, ƒ/5.5, at best focus for imaging

Newtonian Reflectors

•  The Basic Newtonian •  Newtonian w/ Ross Coma Corrector •  Paraboloid w/ Wynne Coma Corrector

Newtonian Reflector 200mm aperture, ƒ/4.5

Newtonian Reflector 200mm aperture, ƒ/4.5

Newtonian Reflector 200mm aperture, ƒ/4.5

Newtonian Reflector w/ Coma Corrector 250mm aperture, ƒ/4.5

Newtonian Reflector w/ Coma Corrector 250mm aperture, ƒ/4.5

Paraboloid with Wynne Corrector 300mm aperture, ƒ/3.3

Paraboloid with Wynne Corrector 300mm aperture, ƒ/3.3

Cassegrain Telescopes

•  Classical Cassegrain •  Ritchey-Chrétien Cassegrain •  Ritchey-Chrétien w/ Focal Reducer

Classical Cassegrain ƒ/3 primary, ƒ/8 overall

Classical Cassegrain ƒ/3 primary, ƒ/8 overall

Ritchey-Chrétien Cassegrain ƒ/3 primary, ƒ/8 overall

Ritchey-Chrétien Cassegrain ƒ/3 primary, ƒ/8 overall

Ritchey-Chrétien Cassegrain ƒ/3 primary, ƒ/8 overall

Ritchey-Chretien Cassegrain w/ Focal Reducer 200mm aperture, ƒ/3 primary, ƒ/6 overall

Ritchey-Chretien Cassegrain w/ Focal Reducer 200mm aperture, ƒ/3 primary, ƒ/6 overall

Corrected Dall-Kirkham Cassegrain 300mm aperture, ƒ/3 primary, ƒ/7 overall

Corrected Dall-Kirkham Cassegrain 300mm aperture, ƒ/3 primary, ƒ/7 overall

Schmidt-Cassegrain Telescopes

•  Classical SCT (has severe coma) •  Coma-Free SCT (has field curvature) •  Aplanatic SCT (wide, flat field) •  Coma-Free SCT w/ Field Flattener •  SCT w/ Hyperstar module (very fast)

Classical Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Classical Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Coma-Free Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Coma-Free Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Coma-Free Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Coma-Free Schmidt-Cassegrain w/ Field Flattener 200mm aperture, ƒ/2 primary, ƒ/10 overall

Coma-Free Schmidt-Cassegrain w/ Field Flattener 200mm aperture, ƒ/2 primary, ƒ/10 overall

Aplanatic Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Aplanatic Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Aplanatic Schmidt-Cassegrain ƒ/2 primary, ƒ/10 overall

Schmidt-Cassegrain Telescopes Coma-Free versus Aplanatic

Hyperstar Astrographic Module 280mm aperture, ƒ/2 primary,ƒ/2 overall

Hyperstar Astrographic Module 280mm aperture, ƒ/2 primary,ƒ/2 overall

Heavy-Duty* Astrographic Cameras

•  Maksutov-Cassegrain •  Schmidt-Cassegrain •  Corrected Dall-Kirkham Cassegrain •  Riccardi-Honders Astrograph •  Harmer-Wynne Astrograph

* aperture > 300mm, wide-field, short focus

Maksutov-Cassegrain Astrograph 300mm aperture, ƒ/5 overall

Maksutov-Cassegrain Astrograph 300mm aperture, ƒ/5 overall

Schmidt-Cassegrain Astrograph 300mm aperture, ƒ/5 overall

Schmidt-Cassegrain Astrograph 300mm aperture, ƒ/5 overall

Corrected Dall-Kirkham Astrograph 300mm aperture, ƒ/5 overall

Corrected Dall-Kirkham Astrograph 300mm aperture, ƒ/5 overall

Riccardi-Honders Astrograph 300mm aperture, ƒ/3.5 overall

Riccardi-Honders Astrograph 300mm aperture, ƒ/3.5 overall

Harmer-Wynne Astrograph (“Hyperion”) 315mm aperture, ƒ/8 overall

Harmer-Wynne Astrograph (“Hyperion”) 315mm aperture, ƒ/8 overall

Optical Configurations for Astrophotography

Imaging the Sky 2012 Intel HF-3 Auditorium, Hillsboro, OR

May 5-6, 2012 Richard Berry