Introduction

The problem

Equatorial geared mounts that move at the same rate as the Earth
cameras such as the Pentax K-3 and K-1 with astro-tracer function (sensor moves with GPS referencing) – giving up to 5 minute exposure!
Expose to minimise visible motion – exploit ISO, aperture & focal length

Dark skies do exist – and Australia has a lot of them compared to our Northern Hemisphere cousins

Use software and internet tools to assist you

Google Earth to scout locations
determine accurate timing of moon rise, sunset etc –
software tools that allow for location, time such as
- Photographers Ephemeris (http://photoephemeris.com/)
- Exsate Golden Hour (https://play.google.com/store/apps/details?id=exsate.goldenhour&hl=en)
locate the stars you want with Stellarium (http://www.stellarium.org/)
eg where is the Southern Cross or the Milky Way?

Camera with bulb (lock shutter open) or manual mode you need to control shutter speed, aperture, iso
sturdy tripod – one you can weigh down is useful too
wide angle lens
- Micro 4/3 sensor : between 7 and 14mm
- APS-c/APS-h sensor : between 10 and 17mm
- 35mm sensor : between 14 and 20mm
preferably fast (eg f2.8 or better)
intervalometer to time exposures if longer than 30s
remote release for the camera (reduce vibration)
warm clothing – it can get cold out there!

Exposure is the light level you are exposing for measured in EV based on the ISO, aperture, and shutter speed
negative EVs are often used
- -6 to -7 EV is a good range for detailed images of the Milky Way, assuming no light pollution and no moonlight
- -8 EV or lower (-9, etc.) Will probably be a little over exposed, (lower exposure slider when processing to hide noise)
- -5 EV or higher (-4, -3, etc.) Will probably be a bit too dark, (raise the exposure slider when processing at the risk of introducing more noise)

Dark frame subtraction
- ON or OFF?
  - If ON this will result in an exposure after the image you take of the same duration
- Just one dark frame for all?
Image stacking – just like a macro! (http://deepskystacker.free.fr/english/index.html)
batteries – the fresher the better, and several of them for lots of exposures
dew and condensation on your lens
scenery

From film days the 500 rule exposure time at night is
- shutter speed =
  500 ÷ (focal length x crop factor)
- based on grainy film – and it’s a bit inaccurate
Sensor size has variations:
- for a 35mm sensor 500 ÷15mm = 33s
- for an aps-c sensor 500 ÷ (15mm x 1.5) = 22s
- for a micro 4/3 sensor 500 ÷ (15mm x 2) = 16s
it’s a rule of thumb – so it may require some adjustment
find the best exposure to stop star trails

NPF rule accounts for pixel pitch & aperture & focal length
- Pixel pitch = physical width ÷ pixels across sensor x 1000
This is important as it allows for the sensors ability to capture more photons (think of a deeper or larger bucket)
shutter speed = (35 x aperture + 30 x pixel pitch) ÷ focal length

Examples for common sensors (I won’t even mention 645 cameras!):

This link in PetaPixel allows you to view the spreadsheet with the calculator and adjust for your camera

Set black level to not clip blacks
enable lens profile corrections for lens used (or choose a similar lens)
remove chromatic aberration
perform luminance noise reduction – zoom in on the image where some noise and fine detail show. Adjust the noise reduction sliders to reduce noise without affecting detail
optional: modify curves to boost faint astro signals
sync all exposures (if you have performed multiple exposures)
stack