simplified astrophotography by pat hanrahan• allows astrophotography to be far more practical. –...
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Simplified Astrophotography
By Pat Hanrahan
Simplifications
• No laptop computer• Very few wires • Very little power demandBut• No guiding• Limited views for focusing – just the
camera screen.– Stiff neck & odd angles
Point & Shoot Cameras• Useful for quick photos
through telescopes of bright objects– Moon (near Full Moon)– Sun (with Solar Filter)
• Not useful for deep sky objects (e.g., galaxies & nebulae)
• Problem: Automatic features often cannot be turned off!
• Point & Shoot camera is handheld by holding both the camera lens and eyepiece together.
• Tricky part = getting camera square with eyepiece.
Point & Shoot Camera with C-8 Telescope
Point & Shoot CameraC-8 TelescopeFirst Quarter Moon
Point & Shoot
•Moon age beyond Full
•Major Seas clearly visible
Close-up of theupper right part of theprevious picture
Mare Crisiumwith crater near the easternedge of the moon nicely highlighted
Point & Shoot CamerasAdvantages Disadvantages
• Inexpensive & you probably already own one.• Quick
• Automatic features usually cannot be turned off
– Autofocus – Auto-exposure
• Limited to bright subjects (sun/moon)• Lens cannot be removed or changed.
Camera on a Tripod• Allows time exposure pictures &
eliminates shaking.• Earth’s rotation causes stars to
form streaks after about 10 second exposures (for 50 mm lens).
• FAST ISO required to capture stars without streaks.
• Break the rules. – 1600 ISO works great.– Film: Pushing ISO is needed.
ISO = “film” speed
Comet Hyakutake (1996) 15 second exposure 1600 ISO film; Larch Mtn.
Comet Hale-Bopp (1997); 1600 ISO Color Film
Digital SLRs*
• Allows astrophotography to be far more practical.– Cheaper, easier to use as compared to
specialty astronomy CCD cameras. – Multipurpose – Very sensitive– Allows more camera control over “point
& shoot” cameras.– Bigger chip (but many are only 60% of
35 mm film size).Canon Rebel xt introduced in 2003 was first DSLR < $1000 to seriously compete with specialty cameras and film. * DSLR = Digital Single Lens Reflex camera.
Canon Rebel Xt; 1600 ISO; 10 seconds; 50 mm lens; Simple Tripod: No Tracking
Picture Analysis: Inverted colors & Text added; Sky Atlas 2000 Detective Work
Alpha & Beta Centauri
Manual analysis. Note Proxima Centaurus @ mag 10.7
15 Min Time Exposure with Fixed Tripod: South Celestial Pole
The Earth Moves!
Dramatic pictures can be taken with time exposures with moonlight or artificial light.
Photo by Getty Images
Moonrise at OSP – Aug 2008
At the end of a long evening of observing, the crescent moon provided a surprise photo opportunity.
Camera on Fixed TripodAdvantages Disadvantages
• Quick• Longer exposures OK (limited by sky movement).• Wide Field pictures of constellations & Milky Way are possible
• Mainly limited to wide field camera lenses.•Telescopes magnify sky motion too much • Limited to short-term exposures without having star trails.
Camera on Tracking Tripod
(but not “guided”)
Orion EQ-2 Mount
Tracking: Follow general motion of earth’s rotation.
Guiding: Corrections used to get an exact motion of earth’s rotation (star movement).
Piggyback mount for C8 telescope (similar mounts available for other scopes)
Mount simply allows you to attach a camera “piggybacked”onto a tracking telescope. The optics of the telescope are NOT used.
Piggyback mounts are available for other telescopes too.
Comet 17P/HolmsDecember 2007Canon Rebel Xti with50 mm lens
(single 30 s exposure)
Jupiter, Sagittarius, Milky Way; 17 mm Fish Eye Lens
Raw Picture (Single Image) Processed Picture
Ursa Major & Mt. Hood: June 2008; 17 mm Fish Eye Lens
Large Magellanic Cloud; Australia, Dec 2007, 50 mm Lens
Stack of 6 best pictures (30 s each )
Tarantula Nebula in bottom of LMC
Southern Cross, December 2007, 50 mm Lens
Stack of multiple 30 s exposures & enhanced with Photoshop
Analysis of previous picture by Astrometry.net (free but need to register)
July 31, 2008
Andromeda Galaxy (M31)Canon Rebel Xti with 75-300 mm telephoto lens @ 200 mm
No telescope ; Series of 30 sec exposures on tracking tripod without guiding
July 31, 2008
Orion Universal Camera Adapter 1 1/4"
Caution: Some adaptors are too long and prevent focusing!
T-Ring
Camera Telescope Connections
Prime Focus
(No Eyepiece)
1997 Comet Hale-Bopp (head)
C-8 Telescope with tracking
(Film)
Omega Centauri – Canon Rebel Xti – C14 TelescopeStack of 30 sec. exposures
Eta-Carina Nebula; Dec 2007; C-14 Telescope
Hubble Space
Telescope vs.
Pat’s Picture
Centaurus-A Galaxy
Tarantula Nebula in LMC; C-14 Telescope
Stack of 14 Pictures x 30s each
Guided Photography• Simple “Tracking” mounts have errors that
can ruin long exposures.• Solution is to use 2 telescopes, a laptop,
software, lots of cords, and lots of power:– One telescope for imaging– One (cheap telescope) for tracking a single
guide star– Information from guide star is sent to a laptop
computer which gives motion commands to the mount
• In the “Good Old Days” this was done by hand!!
Guided astrophotography is equipment intensive!
Leo Trio of Galaxies. 12” Meade Telescope; Scappoose, OR Spring 2008
Bubble Nebula (NGC 7635) by Chuck Rahe
Caveats For Astrophotography in General• Focusing is one of the biggest problems
–Cannot simply turn lens to “∞” position
• Digital Picture enhancement (stacking, curves, levels) is needed to bring out a good picture.
• Deep “Red” nebula require longer exposures with digital cameras.
Caveats For Astrophotography in General• Best pictures result from combining a
number of short exposures (to make a long exposure)
• “Dark” Frames are used to eliminate some digital noise.
• START SIMPLE– You can easily wreck a hobby by getting too
much “stuff” too soon.– Remember this is a hobby and not a job.– Creativity is more important than stuff.
• There will always be someone who takes better pictures than you do.
• Enjoy what you create and be proud of YOUR work.
• It probably still will exceed the work of many astrophotographers of a generation ago
Burnham’s Celestial Handbook, Vol. 1, p. 16
The Biggest Caveat