Imaging Procedure

For controlling the camera, I use Christian Buil's IRIS program for both video and stills. The software supplied with the camera works but it is not designed for astronomical imaging and is best left in the box. IRIS (see Chapter 6) is freeware and includes extensive image processing functions. All that is generally needed is to set the exposure manually, using slider bars, until all the detail is visible and

Figure 3.7. Composite image of Saturn and four of its moons taken by Keith Mallelieu and David Ratledge. Saturn imaged using a Celestron C11 and its moons with a 16-inch Newtonian. For Saturn, the best 150

frames from a 600-frame sequence were processed using Registax. Wavelet filters were used to sharpen the image and reveal traces of Enke's division.

Figure 3.6. "Pentax" Toucam on 16-inch Newtonian. The CCD could be regarded as "air-cooled," which does improve performance!

Figure 3.8. The

Straight Wall on the Moon: main image best frames from 4 videos taken at the prime focus of a 16-inch Newtonian. Inset: best frames from 5 videos with 3x converter lens. Both sharpened with a combination of unsharp mask and wavelet filter in IRIS.

Figure 3.8. The

Straight Wall on the Moon: main image best frames from 4 videos taken at the prime focus of a 16-inch Newtonian. Inset: best frames from 5 videos with 3x converter lens. Both sharpened with a combination of unsharp mask and wavelet filter in IRIS.

then perhaps tweak the brightness a touch. It is important to avoid overexposure - burnt-out detail is lost forever.

For the planets I connect a 3x converter lens on the camera body, and this provides an image scale of around 250 pixels for the size of Jupiter's disk. In the case of Mars, I use a 3x and 2x in tandem. For the Moon, either prime focus or a 2x converter is generally enough magnification (see Figure 3.8). Focusing on the planets can be difficult at high magnification because of seeing fluctuations but if the Moon is nearby its bright limb can be used to find precise focus.

Initially I took stills of the planets and the Moon. However, I soon learned that video is better - much better. With video, hundreds of images can be captured in seconds! The limit becomes disk space as 200 images at 640 x 480 equates to about 90Mb. Before you know it 1Gb of disk space can have vanished! Generally, though, the more images there are to select from, the better the result will be. For Jupiter the limit becomes how long before rotation of the planet starts to cause blurring (see Figure 3.9). I personally limit videos to no longer than one minute in which time, at 10 frames per second and allowing for some losses, 500 images can be collected. From these, the best 50 can be selected automatically during processing.

Figure 3.9. Jupiter and 2 moons - best frames from 3 videos Processed using IRIS, which automatically selected the best frames.

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