Fixed Tripod - Prime Focus The Full Moon Prime-focus means the camera is hooked directly up to the telescope. The scope takes the place of the camera lens. No eyepiece is used in the scope, and no camera lens is used on the camera. Because the full Moon is so bright, really short exposures can be used on a fixed tripod, so the Moon will not be blurred or trailed from the Earth's rotation. The longer focal length of a telescope or long telephoto is needed to get a large enough image size of the Moon to see detail on it.

The nearly full Moon gets set to occult Antares, the brightest star in the constellation of Scorpius.

Antares is just barely visible at the upper left, very close to the Moon's limb. The short exposure for the bright Moon was not long enough to make Antares appear very bright, and reducing the image's size for this display made Antares even smaller.

This photo was taken at 10:46 p.m. just before the edge of the Moon occulted Antares. This photo was taken about 15 hours and 26 minutes before the exact time of full Moon.

It was shot at ISO 400 at 1/400th second at f/6. This is almost two stops, or four times more exposure than recommended for the full Moon at f/11 with the "Looney 11" rule. This was done because the Moon was not very high in the sky and the atmosphere was very hazy, making the Moon considerably dimmer than it should have been. Also, I used the longest exposure that I could without clipping any highlight detail on the Moon, so that I could try to get Antares to show up in the image. Antares was considerably dimmer than the full Moon, and would have taken a much longer exposure for it to show up prominently. But with a much longer exposure, the Moon would have been completely overexposed.

This is the great thing about digital cameras. You can take a test exposure, examine the image and its histogram on the LCD on the back of the camera, and make adjustments in real time.

Image Data

• Lens / Scope: Stellarvue SV70ED ED doublet refractor
• Focal Length: 420mm
• F/stop: f/6
• Exposure: Single 1/400th-second exposure
• Mount: Fixed tripod
• Guiding: None
• Camera: Unmodified Canon EOS 1000D (Digital Rebel XS)
• Mode: JPEG
• ISO: 400
• White Balance: Daylight
• In-Camera Noise Reduction: Off
• Filter: None
• Temp: 70F
• Start Time: 10:46 p.m.
• Date: June 6, 2009
• Location: Voorhees, NJ
• Calibration: None
• Processing: Standard in-camera JPEG processing. Image cropped and sharpened a bit in post processing.