long exposure photography

Introduction

long exposures can be used for:
- how to blur water motion - waterfalls, seascapes, etc
- creating moving cloud landscapes or seascapes
- urban night photography
- astrophotography

General technique

use a tripod and turn off the image stabiliser
- avoid windy conditions as this will shake the camera during the exposure
- take care that the tripod does not move during the exposure - on beaches, it may sink slowly in the sand!
avoid camera shake by using either:
- the camera's self-timer
- a remote shutter release cable, or,
- remote control of camera via a smartphone
decide whether or not you want to have long exposure noise reduction turned on or not
- long exposures create thermal (heat-induced) digital noise in the image which shows as “hot” pixels
- long exposure NR setting makes the camera take a 2nd shot immediately after with the same exposure duration but without recording the scene thereby only recording the “hot” pixels which the camera then automatically subtracts from the scene image to save you the trouble in doing this in post production
- the big downside to long exposure NR is that is wastes your time - and if a scene is changing quickly such as at sunset, you may not be able to afford to waste this time
- there are two alternate options:
  - if shooting landscapes, one could just manually remove obtrusive hot pixels in post-processing
  - if shooting astrophotographic landscapes of the Milky Way, manual removal of hot pixels is not easy as they are confused with stars, so astrophotographers generally use another technique - shoot your own “dark frame” image - a shot with same ISO and exposure duration at same camera temperature with the lens cap on, and then manually subtract this “dark frame” from your main image in any software that allows layers (eg. Photoshop)
use a filter to allow long exposures during daylight hours
- this is not needed for astrophotographic landscapes of the Milky Way or urban night photography, but in brighter conditions, you will need a ND filter to reduce the amount of light hitting the sensor
- how strong the ND filter is depends upon how bright the scene is and how long you want to expose for and the aperture you desire to use, but you will probably wish to use a 10 stop ND filter (eg. ND400)
- using a strong ND filter like this with an optical viewfinder on a dSLR makes it hard to compose the scene or to focus, so you will need to do this without the filter in place or resort to Live View (this is not an issue with mirrorless cameras)
- ensure there are no light leakages as these will impact your images - hand holding a filter will cause light leakages - buy the correct size filter for the lens or use stepping rings to adapt the filter for your lens
set camera to manual focus
- many cameras will not be able to autofocus well through a ND400 filter, so lock in your focus before attaching the ND400 filter
shoot in RAW + jpeg mode for best post-processing image quality
set camera exposure mode to MANUAL
- this gives you full control of the 4 “settings” that determine your exposure (but remember the light may change quickly so you may need to keep adjusting these settings to keep the exposure correct for the light):
  - ISO:
    - set ISO to the base ISO for the camera for best image quality (eg. ISO 100 or 200 depending upon camera)
    - most cameras have an ISO setting lower than this which could be used to gain longer exposures but at a cost of image quality in terms of dynamic range, etc.
    - for astrophotographic landscapes of the Milky Way, you will probably need ISO 1600-3200 to capture the Milky Way well without star trails
  - lens filter strength
    - ND8 = 3 stops
    - ND400 = 10 stops
  - lens aperture
    - for astrophotographic landscapes of the Milky Way, you will generally want to widest aperture possible to capture as much light of the Milky Way as possible
    - for most other images, you may wish to stop down the aperture (eg. to f/5.6 on Micro Four Thirds system or to f/11 on full frame cameras) to not only give a wide depth of field (DOF), but also to minimise the amount of light coming in so that you can shoot a long exposure without over-exposing the image
    - hint: if you use a small aperture, this will show up any dust on the sensor so ensure you have cleaned the sensor first
    - if you use really small apertures such as f/11 on Micro Four Thirds system or f/22 on full frame, you will lose detail due to diffraction effects and end up with a softer looking image
  - shutter speed
    - mostly you will want 60sec - 4 minutes for urban night photography or how to blur water motion - waterfalls, seascapes, etc
      - Olympus cameras allow timed long exposures to 60secs in normal mode, and Timed BULB to 1,2,4,8,15,20,25 or 30min in addition to Live modes
      - most other cameras only have timed shutters to 30secs then you must use Bulb mode which requires one to terminate the Bulb exposure manually.
    - for astrophotographic landscapes of the Milky Way, the exposure duration is determined by whether or not you wish to see star trails
      - to avoid star trails you need to keep exposure short enough for the focal length of your camera, so you may be using only 10-20secs
Olympus camera users have a few other unique options
- long exposure modes in Olympus cameras

bring a spare battery, especially if it will be cold
bring a torch if shooting at sunset so you can find your gear when packing up and get back safely after dark