Imaging the Moon

Digital cameras

Most low-end digicams have a fixed optical system, with non-removable lenses, and some may not even have an LCD (liquid crystal display) screen, so the principles involved in photographing the Moon through these cameras are just the same as with afocal photography using conventional fixed lens film cameras (see above).

As a general rule, the digicam with the highest pixel rating will produce the clearest, highest resolution views of the Moon. Most digicams can take images in a number of resolutions – a low resolution image will take up less space in the camera’s memory, and more images can be stored. Lunar photography requires the maximum resolution possible, so the setting should always be on high.

Most digicams provide instant results, their stored images being viewable on the camera’s small LCD screen. The photographer can review each image individually to decide whether it’s good enough to keep, or whether to delete it and free the memory for a better image. LCD screens are usually on the small side, and the display is coarser than the captured image itself. To save the amount of time spent focusing the image, first focus the Moon in the eyepiece using your own eyes. When the digicam is fixed to the same eyepiece, the focus ought to be about right. Fine focusing is best achieved by viewing along the lunar terminator, where most relief detail is thrown up by the low elevation of the Sun, and features appear at their sharpest. If the digicam has a zoom facility, the lunar terminator can be magnified, aiding focusing further. By hooking a digicam to a TV monitor or PC screen, the problems of focusing using the camera’s inbuilt LCD screen are bypassed, as a larger image is far easier to gauge a focus.

Digicams are designed for everyday use, and their automatic settings may pose considerable problems when attempting to photograph the Moon, so it’s essential to experiment with the digicam’s various settings to produce the best results. One of the most important settings to get to grips with is the digicam’s exposure settings, as many afocal lunar images tend to be somewhat overexposed, the bright part of the Moon appearing washed out and lacking in any detail. The digicam’s automatic exposure works best if there is a uniformly bright image across the entire field. A digicam may judge exposures perfectly fine when the Moon is centred in the field of view or when taking close-up shots.

Colour images of the Moon taken with digicams may show particularly vivid tones that aren’t visible through the telescope eyepiece. While colour can enhance the aesthetic quality of an image, it can also be undesirable. Computer processing can easily tone down any colours in an image. Capturing the Moon’s colours in an exaggerated or visually realistic fashion may produce a pleasing image, but the same amount of topographic detail can be recorded in black and white. If your camera has a facility to take black and white images, try it out – the results may be noticeably sharper than those taken in colour. Black and white images will take up less space in the camera’s memory, too.

Using the digicam’s zoom facility (if it has one) can eliminate the problems of image vignetting that tends to plague afocal photographs. Zooming adjusts the position of the camera’s internal lenses – the magnified image becomes progressively dimmer, and vibrations in the telescope will show up more. When ‘digital zoom’ comes into play at high magnifications, the quality of the image begins to degrade and the advantages of zooming are completely cancelled out. Optimum zoom is not maximum zoom – the amount of zoom used depends on the seeing conditions, the resolving power of the CCD chip and the telescope, as well as the stability of the system and the accuracy of the telescope drive.