Webcams and Digital Imagers 357

For those of you who have not read my last article, my policy on twit mail stands.

Before you ask I will answer your first question: “Why is there an astronomy
article on an overclocking website?”.

The advancement of astronomy requires
science to find ever-fainter scraps of light and probe deeper into what was
once considered the purest of darkness. This means the advancement of
technology is the limiting factor of new research. This is where overclockers
come in.

Most astronomers would prefer to watch the stars than fiddle with a
camera. If not, then this is an off-topic general interest article. Most of
you have little need for a faster computer (aside from frame rates and all
important bragging rights), so I want to bring to your attention a technology
undergoing its formative period:

Webcams and Digital Imagers.

These little
consumer devices hold real potential in science if they are modified to do
so and given (or written) proper software. I am looking to start a discussion
amongst a group of people who do not work with the astronomical community
and would not normally think to apply their skills.

I would like to know your thoughts on this topic.

It should be noted webcams cannot, even in
theory, match the performance of a purpose built, low-light CCD detector, but
there are many things you can do you could not hope to with a full size
sensor. I should also note consumer digital still and video cameras will, in
most cases, work just as well (if not better) as webcams if frame rate is
not a concern.

Webcams are very good at collecting a small (300,000 pixels * 3 colours)
amount of information thousands of times a second, then compressing it into a
manageable size. Almost all webcam sensors have 5.7 micron pixels and have a
3.65mm by 2.74mm imaging area. This limits you to one object at a time, for
all practical purposes.

At this point in astronomy, there are a number of high resolution, all sky
surveys in progress or completed (2MASS SDSS, 2DF, CFHTLS, etc.). These are
designed to give astronomers a starting point on which to base future
research with the next generation of telescopes. The resolution of these
surveys is limited by the atmosphere, meaning there is very little ground
based astronomy left to do.

This leaves you with two options:

1. Watch for changes and moving objects, or
2. Find a way around the limitations of the atmosphere.

Either way you need three devices:

• A telescope
• A camera capable of high frame rates
• A whole lot of extra CPU power lying around

Most
of you have two out of three and, for most of these applications, you can get
away with spending less on a telescope than you did on your last motherboard
and CPU upgrade (double if you want an out of the box solution).

On to what you can do with a webcam:
{mospagebreak}

For most of these, there is little in
the way of modification needed. In fact, most of these tasks are a
matter of processing the information and can be done with a little
programming. For many, there are already programs to do the same thing but
could use improvements with automation and/or user friendliness (not to
mention cost). If you want to do serious modifications, a good place to start
would be HERE, where you will find out how to gain full control of exposure time and upgrade the sensor.

What you must remember about astronomy (and photography) is it is not about
light – there is plenty of light in the world. Imaging is a question of
cutting out the light you don’t want, then compressing the rest into the
smallest possible area.

First upgrade you can make to any imaging device is the lens. The quality of
the lens limits the performance of the system. Make sure it is properly
focused

Second is light baffling. The purpose of baffling is to cut off all stray
light from contacting the sensor. Paint the inside of the camera flat black.
Place a diaphragm in front of the sensor which only allows the light from
the field of view to contact the image sensor.

Dark frame subtraction is based on the fact noise builds on an electronic
sensor at a predictable rate at a given temperature. If you take a
photograph of nothing (ie with the lens cap on) for the same length of time
at the same temperature, then subtract it from the original image. Doing this
will leave you with a clean smooth looking image.

CCD sensors are highly sensitive to heat, not because they will burn out but
because the sensor will convert it into electrons and confuse it with light.
Cooling the sensor will significantly reduce noise.

Satellite Tracking

Presumably you remember the recent shuttle disaster. You likely also know
one of the safety measures now being called for is a system to inspect the
space shuttle for damage while it is in orbit.

All you need to do this in
your back yard is a fast enough mount and a decent means to deal with the
atmosphere. Could you have seen the damage which is suspected of causing the
failure? Maybe. You would certainly need a large telescope and you
definitely would need to know what you were looking at.

Programs exist
(Heavenscape.com) which already know how and where to look for
artificial satellites. There is nothing particularly special about imaging
satellites; the most important factor is frame rate, because your subject will
appear to rotate due to the change in perspective.

Near Earth Object Tracking

It may surprise you to learn this, but there are fewer than five telescopes
dedicated to looking for, tracking and cataloguing near earth objects with
the potential of causing mass extinction.

Furthermore all the dedicated
telescopes are in the 1m class (32″ – 48″) and in the northern hemisphere.
Much like SETI, this program can use all the help you can offer (unlike SETI,
you are allowed to name whatever you find).

Finding Near earth objects
(NEOs) is a straight forward operation. Take an image of one part of the sky.
Take an image of the exact same part of the sky about an hour later then
subtract one from the other. Anything left is either moving or changing.

You
will then need to follow up the discovery over several nights to determine
what the object is, where the object is, and what its trajectory around the
sun is. True, this is easier said than done, but it is all Newtonian physics,
so it can all be automated.

The most helpful thing you can do for this
program is to refine measurements so predictions can be made further into
the future.
For more information on this (although it is not amateur oriented) I would
recommend looking into the LINEAR and NEAT programs.

Variable Star Observing

If you’re interested in this, look into AAVSO.org). This is a
much overlooked field by astronomers, because it takes years (decades and
centuries) to gather enough information for a proper study. This work needs
to be done to better understand the sun and the evolution of the universe.

Binary System Observing

This is roughly the same process as near earth object tracking.

The process is to
compare the motion of stars against the background. If you take the
images six months apart, you end up with a stereo image, with a baseline the
diameter of the orbit of the earth. It is basic trigonometry to calculate
the distance of the object. If you take several images (about every week or
two) over the course of a number of years, any wobble (back and forth motion)
will indicate a companion (although it is not as accurate as spectroscopy
for finding planets). Once again, this can all be automated.

If I have not yet bored you to tears, I highly recommend reading one of Ed’s
fine editorials on copyright law. Next article, I will continue with adaptive
optics, spectroscopy, and cooling the sensor (ie. interesting and practical
applications).

Ian Anderson – Anderson Fine Machinery