Wide-field astrophotography

by

Kym Haines

Image Credits: All images by Kym Haines unless otherwise attributed.

Objective

• Take pictures of the night sky

• Introduce pixels and field of view

SPSP 2017

Sagittarius / Milky Way

DSLR on tripod

And …

• Dark sky

• Fast lens (small f/stop number, e.g. f/1.8)

Lens terminology

• DSLR lens: – Focal length

– Aperture range given as f/stops

– E.g. 50mm f/1.8

• Telescope: – Aperture

– Focal length

– f/ratio

– E.g. Skywatcher Esprit 100 has: • Aperture 100mm

• Focal length 550mm

• f/ratio 5.5 = 550 / 100

Effect of f/stop (f/ratio) on exposure time

Exposure settings

SPSP:

14mm f/2.8 30sec ISO4000 Sagittarus:

50mm f/1.8 10sec ISO4000

Camera settings

Manual mode Shutter speed around 10-30 sec Aperture as fast as possible (smallest f/stop)

Shutter speed

• 500 / focal length = max exposure time

• To avoid star trails

• E.g. with 50mm lens: 500 / 50 = 10 seconds

• 14mm lens: 500 / 14 = 36 seconds

ISO 2000 - 4000

Focusing

Image file format

Shooting

Timer Interval timer

Some pictures

Orion 34mm f/3.8 20sec ISO4000

500 / 34 = 15 seconds detail

Orion 28mm f/3.5 10sec ISO4000

500 / 28 = 18 sec detail

SPSP 2017 Open Competition 12mm 30sec (500/12 = 42sec)

SPSP 2017 Open Competition 90mm 180sec (500/90 = 6sec)

Longer focal lengths / longer exposures

• 500 / 90 = 6sec not 180mins

• Longer focal lengths tend to mean higher f/stop numbers

• 90mm has f/5.6 - need longer exposure time to compensate

Tracking camera mount

www.bhphotovideo.com

Multiple shots

• Combining to give a better single photo – see stacking

– Stars move

– Foreground doesn’t

• Time lapse – see Greg’s presentation

Field of view

Field of view

Targets

• Wide-angle: large or small parts of Milky Way

• Interesting foreground with Milky Way in background

• Tracking mount: just limited by the size of lens; e.g. with full-frame DSLR: – 14mm field of view of 114 degrees Milky Way

– 28mm 75 degrees

– 50mm 47 degrees Orion

– 100mm 24 degrees

– 200mm 12 degrees Southern Cross

– 300mm 8 degrees Witch Head Nebula

– 500mm 5 degrees Eta Carina Nebula

• Who needs a telescope?

More

• In-camera long-exposure noise reduction

• Camera mod-ing

• Intervalometer – external interval timer (more than 30sec)

• Stacking of multiple shots – session 3

• Image calibration – session 7

• Dew