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