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TRANSCRIPT
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