Practicing for the Eclipse
You can prepare to photograph a total solar eclipse by taking practice pictures of the moon during various phases
A solar eclipse happens "around" the moon and the corona will extend two to five times the lunar diameter. Don't worry if your 200mm-lens system does not reveal lots of lunar detail. The moon's surface is very bright by comparison. The goal is not to get great lunar pictures but to practice using the camera and lens system.
The amount of light you will have to work with is about the same as during a full moon meaning that you should have little to no trouble reading the exposure settings on your camera. As you look through the lens, the brightness will be about the same as a quarter phase moon (or less).
To learn just how long of an exposure your system can take, and get crisp detail, try taking a series long moon exposures to get a feel for the movement of the moon. The best time to try this is during the crescent phases, when you can see the Earthshine on the entire surface of the moon.
Star trails are not a desired effect in solar eclipse images. You can experiment with different time exposures to see when trails begin to show in the images. During the eclipse you will want to keep your exposures less than any image that shows star trails.
The partial phases of the eclipse can be photographed using a solar filter if you have a longer lens or telescope. The amount of light will lesson during the eclipse requiring changes to the exposure setting. You can find the proper exposure ranges for your configuration by taking a range of solar pictures. Vary the time from noon to near sunset or with variable cloudiness. If you have a telescope, the right exposure should also show sunspots.
It is important to have a strategy in mind when getting ready to photograph the eclipse. The best rule of thumb is to keep it simple since there is too much to see and experience all at once. You can practice your strategy using the moon and having a good watch to count down the time remaining. My simple strategy is to start with faster exposures around 2nd contact then increase the exposures during the eclipse and finish with fast exposures again as we go into 3rd contact.
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