Simplified Astrophotography By Pat Hanrahan• Allows astrophotography to be far more practical. –...
Transcript of Simplified Astrophotography By Pat Hanrahan• Allows astrophotography to be far more practical. –...
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