The (Slow) Road to Astro-Photography by CCD
by Frank Johns
Successful photography of celestial objects, especially the dim
ones such as nebulae and galaxies, requires that you have a
telescope/mount system which can accurately track these objects.
The reason for this, is these faint objects require long exposure
and it is an unfortunate fact of life that the sky will not stay
still for us.
Even spending £2000 or so on a Meade LX90 with Goto, does not
really achieve the accuracy necessary for good film photographs,
unless of course you are prepared to manually adjust the tracking
for the 20 to 40 minutes required for the exposure.
CCD cameras, on the other hand, can image DSOs (deep sky
objects) with short exposure times, which means the LX90 should be
OK. It is for this reason that I decided to try my hand at it - it
looked easy.
In general, CCD photography consists of taking a number of
images, from several dozen to perhaps over 1000. These images are
then processed in the PC by selecting and stacking in order to
compensate for the short exposure time of each image and to reduce
the electronic 'noise' which is inherent in the single image.
My earliest attempts were to poke my Fuji digital camera down
the eyepiece (Afocal) at the Sun, with a correct sun filter of
course. This gave a good view of the sunspots that were visible at
that time.
My first try at 'proper' CCD imaging were using a Philips
ToUCam webcam. The results were encouraging, the following Mars
picture being typical.
The standard webcam is quite good for the moon and the planets.
However to capture DSOs, longer exposure times are very desirable.
Most webcams can be modified to give longer exposures but such
mods are not for the faint-hearted, in that a slip with the
soldering iron can be death to the camera. I am still bucking up
courage for this.
Soon after playing with the web-cam, I saw an advert for the
Mintron video camera, which promised great things, so I bought
one.
The Mintron camera is primarily used for security purposes,
where it is designed to operate in very low light conditions. The
camera is small and light, as will be seen from the following
pictures.
The Mintron is threaded to receive a range of fittings. Here it
has an 1 ¼ inch adaptor to fit in place of the eyepiece. Screwed
into the end is a f6.3 focal reducer. Other fittings allow
standard camera lenses to be used - I have yet to explore this
aspect.
Once mounted on the telescope, the Mintron can be connected to
a TV set for viewing or through a VCR so the images can be
recorded. The other way to output the images is to connect it to a
computer via a video card. All the work done to date has been via
a computer.
It is easy to connect up the Mintron to the PC and get an image
on the screen. However after that it gets more involved (an
understatement).
The controls are all on the end of the camera, as shown, with
settings made using the 5 buttons seen top left.
There are six steps to achieving a finished picture. These are:
a. Locate the object b. Get the object into focus - accurately c.
Configure the settings on the camera d. Configure the image
capture software to save the image to the PC - in my case I use
Astrovideo for the Mintron imaging e. Align and stack the images
using appropriate software - here I have been using Registax f.
Process the resultant image to achive the desired result - I
currently use Adobe Photoshop
As I said earlier this all seems easy enough! However each of
the above steps proved to range from daunting to 'why did I start
this anyway'.
Most CCD cameras have a very small FOV and so locating the
object requires accurate Goto or skill or luck - certainly
perseverence.
Getting the image in focus is proving to be the most
frustrating aspect. You see the image on the monitor of the PC and
it is very difficult to tell when focus is reached. So far I have
tried a number of methods with limited success. Further, the fact
that the image shifts in an LX90 when adjusting the focus does not
help.
The camera has only 4 items that vary - that's good isn't it?
No it isn't. It turns out each of these has up to ten settings -
those good at maths will realise that this gives …er… well - a
lot of variables.
Once the camera has been set it is only a matter of setting all
the parameters in the capture software and then tweaking the
finished result. This will, I hope, be fine in the future, when I
have learnt to manipulate the two lots of software. In the
meantime it seems like I am back at school , poring over books and
various instruction manuals.
However in spite of all this lack of knowledge, I am blundering
along the road producing the occasional picture which has passing
resemblance to those we see in the magazines. The following
pictures of the Ring Nebula, the Great Orion Nebula, the Moon,
Jupiter and a reprocessed Mars are some of these:
I do feel that I am now getting somewhere and what is good (and
frustrating) about this astrophotography lark is that when you get
an image which you think is not too bad, you read Astronomy Now,
or some other publication, and see the work of others, which tells
you that you have barely started.
