GUIDED EXPOSURES


The Scotch mount or other simple tracking device is easy to use, but for the mount to track accurately there are important considerations to remember.

Before any photos are taken the device must be "polar aligned." Accomplish this by securely attaching the mount to a tripod and tilting the tripod head so that the Scotch mount hinge points directly at Polaris, the north star.

Be certain the hinge is positioned on the left. The top board of the mount should open from right to left like a book cover.

For accurate polar alignment, a short length of 1/2" pipe laid beside the hinge will suffice as a finder scope for Polaris.

 
Ursa Major, the Big Dipper, its handle pointing to the left here, sets just above the tree line in the west. A three-minute exposure at f2.8-4 using 400 film and a Scotch mount.

With the camera securely affixed to the adjustable tripod adaptor on the top board, set the focus at infinity, train the camera on the desired celestial target and lock open the shutter with a cable release. Position the camera carefully. If the set-up is jostled, polar alignment may be lost.

Activate the guide by turning the clockwheel 30 degrees every five seconds (that's one full revolution per minute). For wide angle lenses, the maximum recommended exposure is about 30 minutes; for normal lenses, 20 minutes; for lenses up to 200mm, 10 minutes.

As an alternative, the wheel can be rotated 180 degrees every 30 seconds with wide lenses or 90 degrees every 15 seconds with normal, 50mm lenses.

RIGHT: The open cluster Pleiades rises in the early eastern skies in August 1999. A three-minute exposure using a 35mm lens.


LEFT: The Pleiades again, photographed using the Scotch mount and a 180mm lens.

TIPS: To keep the movement of the shutter from jarring the camera, I have a small can which I drape over the lens. The inside of the can is lined with black paper. I carefully remove the can from the lens a few seconds after the shutter is locked open to be sure any vibrations have stopped. I place the can back over the lens to end the exposure before closing the shutter with the cable release.

Instead of struggling in the dark to watch the clock, I picked up a wind-up clock and listen to the ticks to measure the five-second intervals.

  
LEFT: At a distance of 2.5 million light years, the Andromeda Galaxy is captured with a 135mm lens at f2.8-4 and three minute exposure on 400 ISO film. Using the Scotch mount, every star registers as a point of light.

RIGHT: The Orion Nebula, distance 1,500 light years, photographed with a 180mm lens about 12:15 a.m. on Dec. 11, 1999. The lens aperture was f2.8-4. A Scotch mount was used for the two-and-a-half-minute exposure on Fuji 800 ISO film. Even under moderately light-polluted skies the nebula's wispy gas and dust—an incubator for young and evolving stars—records on film as a reddish glow.

My interest in astrophotography resulted from my frustration in attempting to navigate the stars with a small telescope. The star charts did not correspond with the light-polluted view of the sky from my backyard, so I started taking pictures in hopes of better interpreting what I was seeing through the telescope.

My plan didn't work, but in time, and with the purchase of a better telescope, the view through the eyepiece began to make sense.

And the photos became ends in themselves...



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