See This Next Month

Here's a tip for anyone wanting to photograph the lunar eclipse using a DSLR camera and a standard tripod -- use the '500 Rule'.

Due to the Earth's rotation, any long exposure of the moon and stars will cause the image to move across the camera's CMOS sensor during the exposure, resulting in a streaky image. A too-short exposure will yield an image too dark to see.

To find the maximum exposure time, in seconds, that will produce a useable image without streakiness, divide 500 by the focal length of the camera lens in millimeters. So for example, if your camera lens has a focal length of 50 mm, the maximum exposure can be 500/ 50 = 10 seconds long and still give you stars that look like points.

For capturing stars you'll want to try using the highest ISO setting your camera has, to get the brightest star images. If you get a lot of stars and the image is too grainy, you can then lower the ISO setting, using the '500 Rule' as a guide for the maximum exposure time. (Of course, you can use a shorter exposure time if you want to. The shorter the exposure, the sharper the image will be.)

For the lunar eclipse, the full moon will be very bright at the start, so you'll want to start with a short exposure time and a low ISO value. Perhaps start with an ISO setting of 100 and an exposure time of 1/50th of a sec. If the image is underexposed adjust your ISO higher; if overexposed, shorten the exposure time.

When the eclipse is at total phase, the moon may be very dark. This is when you'll want to use the '500 Rule' to set the maximum exposure time, and adjust your ISO as high as needed to get a bright enough image.

Finally - for anyone who wants to take longer exposures than the '500 Rule' allows, with spending a lot of money on expensive equipment, you can trying making a 'barn door tracker'. (Google that term.) For a few bucks and an hour or two of your spare time, your can make a simple device that will allow you to compensate for the Earth's rotation and take long exposures.