Page 8 - Astronomy Book 1

I use a number of different systems to capture the full range of objects in the
sky. Some objects are very small and require the use of my Celestron 9.25”

telescope. A lot are however large enough that they are best imaged with
small telescopes or even camera lenses.

Although I started using ordinary Canon cameras with several lenses they
did not have great sensitivity to the H Alpha Region of the spectrum. I then
got a Canon 450D modified to remove the IR filter.. This gave much better H

Alpha sensitivity but overall the light gathering power of the sensor array
was limited and the images noisy because the camera was not cooled.
Ultimately I invested in an Atik 383 ccd camera with Peltier cooling.

There are several issues in using camera lenses with astronomy ccd cameras.
The first is achieving focus. Since my overall aim was to image all night,
hopefully as I slept soundly in bed, I needed a way of automatic focusing.
Originally, even with the lens attached to the Atik 383 I was able to also
connect the focus mechanism electronics of the Canon450D. This was

achieved using a Novoflex macro adaptor (see middle picture). This allowed
the Canon to still control the lens and enabled me to use Live View focus
controls remotely while evaluating the Atik images. Eventually I got the
whole system focusing automatically.

This system worked fine with the 500mm lens because it had a special filter
drawer which enabled me to manually introduce RGB and narrowband
filters to the light path. However with other lenses it was impossible to use
a filter and the Novoflex adapter in the light path and still achieve focus. I
needed a different way to focus. I tried a motorised push pull system (see
middle picture) but it introduced too much hysteresis. Finally I opted for a
belt driven system (see bottom picture) which I now use on all my lenses. It

achieves excellent focus automatically using FocusMax software. Not
requiring the Novoflex adapter also enabled me to introduce a
re-engineered TruTek filter wheel to the lens systems

8