Making measurements of the physical dimensions of a planet with small telescopes can be done more easily with digital photography than with a micrometer eyepiece. The micrometer requires experience, skill and a solidly stable telescope mount. Photographic prints can be measured in a warm room at your leisure. Measurable digital photographs of Jupiter, Saturn, Mars and Venus can be taken with an 80-mm refractor or 90-mm Maksutov using a camera with 3-megapixel or higher resolution. Although they won't reveal the rich detail of photos taken with larger instruments, they will provide enough information for some interesting activities. Figures 8.1 and 8.2 are representative photographs of Jupiter and Saturn taken with a 90-mm Maksutov telescope.
Exposure times will be from 1/25 second for Venus to 1/5 second for Saturn, depending on sky conditions and the brightness of the planet. Set the camera for an ISO of 100 and the highest resolution. Good results can be secured using a 6-mm wide field eyepiece and camera set at maximum optical zoom. With a 90-mm Maksutov, a 9-mm wide field eyepiece works well. Follow the instructions in Chapter 5 for setting up the camera. Take a number of photos at each of a few
Figure 8.1. A digital photo of Jupiter taken with a 90-mm Maksutov telescope.
shutter settings. Some will be better than others because of inevitable variations in seeing. Download all of the images to a computer and select the best for measurement. Store them on a disk for safekeeping and later use.
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Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.