The pictures on the album page were taken using a Starlight
Xpress MXC7 CCD camera attched to the telescope. This camera is designed for taking astronomical images, and is capable of
taking very long exposures. Typically though, the images I take are between 15-40 seconds. The picture on the left shows the
camera attched to a focal reducer (in effect this gives a wider field of view), and an electric focuser (closest to the back
of the telescope).
One of the biggest problems I face is focusing, and I deal with this using
the Hartman mask visible on the shelf in the background. This mask looks like a typical telescope dust
cap but with three holes in it. With the mask on the telescope I will see one image of the star only if
it is in focus otherwise I will see three images of the star. The more the image is out of focus, the further apart
the three star images will be.
Focusing is made more complex by the twinkling effect caused
by the star's light being refracted by our atmosphere. This means that as I get closer to that "perfect" focus
point, the star seems to move around very slightly. For an image taken over time - say 15 seconds - the result will be an
unrealistically large star image, especially if its bright.
Other effects come into play such as the tracking accuracy of the telescope,
the alingnment of the telescope mirrors in relation to each other, and electronic noise within the camera itself.
Having taken an image, I do a certain amount of image processing, mainly
to improve the contrast of the image so as to boost the visibility of faint features.
In August of 2008 I updated the scope from my 10 year old "classic" LX200 to a 12" LX200 ACF.
Additionally I had found that a light pollution filter reduces a lot of light interference from my house that looks like
noise on my images. The difference between the images taken between the old and new setup is pretty amazing - just look at
the Ring Nebula on the album page.
