INTRODUCTION TO ASTROPHOTOGRAPHY

Blythe GuvenenKitt Peak Visitor Center

Astrophotography

Astrophotography is a specialized type of photography that involves making photographs of astronomical objects in the night sky such as planets, stars, and deep sky objects such as star clusters and galaxies.

Astrophotography

Astrophotography is used to reveal objects that are too faint to observe with the naked eye.

Digital cameras Can accumulate and sum photons over long

periods of time. Astrophotography poses challenges that

are distinct from normal photography. Subjects are usually quite faint, and are often

small in angular size.

Daguerreotype

First photographic plate, thin film of polished silver on a copper base.

Invented by Louis Daguerre in 1838

Early Astrophotography!First Lunar Daguerreotype 1840 - John Draper

(20 minute exposure!)

Early Astrophotography!Henry Draper

First to photograph the Orion Nebula; September 30th, 1880

50 minute exposure!

The Human Eye

No permanent record of images.

No way to change exposure time.

No good way to measure quantitatively.

To film or not to film?

Pros: Well-established Archival quality

(black and white)

Cons: Finicky to

temperature, humidity, processing conditions

Fragile; brittle Low efficiency: 1-10% Non-linear (reciprocity

failure) Difficult to get

quantitative information

Nearly extinct!

Charge Coupled Device (CCD)

Semi-conductor based solid state detectors

Incoming photons generate electrons that are added up to form an image

Excellent quantum efficiency: 60-90+%!

Available for a wide range of wavelengths: 300 - 1100 nm (Si) 1 - 5 µm (InSb) 1 - 25 µm (HgCdTe)

Astrophotography Using a Camera

Good quality, wide-angle photographs of the night sky can be made by almost anyone using a single lens reflex digital cameras.

Should travel far away from the bright, light-polluted skies. Prevent the photograph from being completely

washed out and ruined by bright urban light pollution.

Fixed-Position Mounting

Equipment needed Camera capable of

long (>30 sec) exposures

Sturdy tripod Techniques

Amount of trailing depends on exposure time and declination

Digital stacking Time-lapse

Tracked Wide Angle Shots Equipment

>30 second exposures Tracking mount Piggybacked camera w/

lens Techniques

Digital stacking Foreground will trail

(unless you use a flash to freeze it)

Short Exposure Astrophotography

Use CCD with “Hyperstar” or modified webcam

Short exposures = less expensive mount Align and stack Exact polar

alignment is less important

Larger periodic error is tolerable

Unguided

Long Exposure Astrophotography

Good mounting is critical Exact polar alignment is

necessary Solid connections (rings,

plates, etc.) Must be guided

Manual or auto Need reticle EP or

autoguider

Long Exposure Astrophotography

Guiding Piggyback

Need adjustable rings Need larger mount Differential flexure

Off axis guider Can be hard to acquire

guide star Built in autoguider

Guides through filter less sensitivity

Astrophotography Using a Telescope

Afocal “Prime” focus Eyepiece projection “Piggyback”

Afocal Photography

Simplest telescope coupling (unguided) - Skylight filter recommended (protect camera lens)

Difficult alignment and focussing Variable results - lots of patience! Good telescope method to start with - Digital cameras

Requires good quality eyepiece

Afocal Coupling

Afocal Photography

Digital Camera Adapters

“Prime” Focus

Camera directly coupled to telescope Telescope objective acts as very long

focus lens Camera replaces telescope eyepiece Focusing easier than afocal method Telescope guiding desirable!

“Prime” Focus

Focus on chip

Cassegrain telescope

Camera

Off-axis guider

Detector

WebCam Astrophotography

Schmidt Camera

Schmidt Camera

“Astrograph”

Questions?