Digital Astrophotography - The early years

First efforts with film

As a kid, my parents had bought me a small astronomical telescope, a refractor with a 60-mm objective lens. Later in my mid teens, after taking up photography, I tried bringing my SLR camera loaded with black and white film up to the eyepiece. Both camera and telescope were on separate tripods and bringing the Moon to the right place in time to get the camera positioned required some skill. The results, however, were reasonable.

This image shows the last quarter Moon. The triad of craters in Mare Imbrium; Archimedes, Autolycus and Aristillus; are easily visible about a quarter way down from the top. Tycho and its rays is visible about a fifth way up from the bottom.

The 150-mm Newtonian

In 1994, with the first telescope having long come apart, I bought an inexpensive Newtonian telescope from John Braithwaite, a telescope maker in the Clyde Valley.

The Moon

Later, I read of people bringing webcams to their telescopes as a way of achieving cheap astrophotography. Since I had an Intel PC Camera Pro webcam, I gave it a try. I removed the plastic shells, then the lens assembly to directly expose the CCD imaging chip at the heart of it. After removing the eyepiece, I taped the contraption to the focussing tube of the telescope so that the prime image from the big mirror landed directly on the sensor. I took it outside, plugged it into my laptop and, once I got the Moon in my sights, recorded what I could. The results were better than expected.

I started by grabbing lots of stills of the Moon, while allowing the Earth to take it through my telescope's field of view. The constant movement of the Earth's atmosphere blurred many of the shots but a few came up very well.

This is a detail of the Moon from this first session, showing Mare Crisium half lit by an evening Sun. The small, bright crater near the centre is Proclus.

Having grabbed a few dozen images, I pasted them together on the computer to get the result below.

The Planets - 2001-12-02

Buoyed by this success, I tried aiming the telescope at Jupiter and Saturn. On single frame captures, the belt structure of Jupiter's clouds could be made out while Saturn and its rings were easy to see.

While trying to set the correct exposure on Jupiter, I noticed that if I overexposed the planet itself, I could image the four major moons of the great planet.

The bright blob in the middle is Jupiter with telescope-induced flare surrounding it. Strung on either side of it are four of its moons.

Image processing

I discovered a computer program called Astrostack that allowed me to take these crude first steps further. Each frame of the video from the webcam displays noise from the camera and its processing, while the constantly moving atmosphere distorts and softens the image quality. Astrostack is one of a feew programs available that allows hundreds of images from a webcam to be selected according to their sharpness then added together to cancel out the effects of random noise and variations. Combined with a little post processing, the image of Jupiter from the webcam is substantially improved.

All in all, an excellent start. However, keeping an object in the CCD's narrow field of view proved to be very difficult. The Earth's rotation quickly takes it out and the telescope has no means of being driven to track the stars and planets. I was ready to move to the next stage.