Astrophotography @
Week 1: Introduction
Goals
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Learn what camera parameters are important for low-light photography.
Practice in the planetarium: Photograph constellations and other scenes that will be important
later.
Introduction
During the course of the astrophotography
workshop, we will need to manually control
three important settings:
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Aperture
Shutter speed
ISO setting
To control these settings, we need to access the
“manual” setting on your D-SLR. For most
cameras, this is marked by an “M” on the
setting dial; however you should consult the
owner’s manual that came with your camera.
Aperture: The aperture restricts the amount of
light transmitted to the sensor. It can be used
creatively in other photography by controlling
the depth of field. However, for dark sky
photography, we will set this to the largest
aperture that your camera allows. That is, set it
for the smallest f/ number. This will allow as
much light as possible through to the sensor.
We don’t have to worry about depth of field
since astronomical objects are very far away.
When we photograph the moon and sun, we
may need to change this.
Set the aperture (red oval) to the smallest possible number.
The shutter speed (yellow) and ISO will be adjusted.
Selecting manual exposure.
Shutter speed: For all of our photos in the
workshop, we will have some relatively long
shutter speeds. So, to prevent blurred images, a
tripod or telescope mount is required (provided
by the workshop). Depending on the subject
and project, we will select shutter speeds as
long as 20 to 30 seconds. Some projects will
require holding the shutter open for longer
periods, like 5 – 10 minutes, using the “bulb”
mode of the camera. All cameras are different
in how they access this mode. Please Consult
your owner’s manual.
ISO setting: This setting controls the sensitivity
of the sensor. Depending on the project, this
may be set as high as the camera allows.
Remember, larger ISO values may contribute
more noise but will allow smaller exposure
times. Smaller ISO values will give darker
images, requiring longer exposure times. We
will use these ideas to tailor other projects
later.
Practice
We will practice in the planetarium
photographing constellations and scenes of
importance. You will be using a tripod and a
modest lens (anything between 20mm 100mm).
Because it’s dark, it’s much more difficult to
focus the camera. Autofocus may, or may not,
work reliably. Moreover, later in the class, we’ll
remove your nice AF lens and use the telescope,
so some practice focusing the camera manually
will be handy. So, here are some ideas to start
low-light photographs. (By low-light, I mean
stars, not the moon). In all of these, the
aperture is set to the smallest f/ number.
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Turn the focus to infinity: “∞”. For many
cameras, this is the farthest you can adjust it.
Often, Canon cameras will allow focus “past”
infinity. This will get you close. Unfortunately,
this will not work inside the planetarium.
A lens focused to infinity (left) and a lens focused beyond
infinity (right). Image credit: http://www.school-of-digitalphotography.com
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Point your camera to the brightest star you can
find. Or (not quite as good) point your camera
to the farthest terrestrial light you see. Look
through the view finder and focus.
One Final Introductory comment:
Later in the class, we will play with more
advanced processing techniques. This will
require saving the data from the camera in a
“Raw” format. Please consult your owner’s
manual.
Winter/Spring Constellation and scenes of
importance for 2014.
Orion, Jupiter, and the moon:
Cassiopeia, Ursa Major, & Ursa Minor
*Image credits: Stellarium v0.12.4
http://www.stellarium.org/ (free)