The AstroTrac TT320 (shown here) and the later model TT320X (identical in appearance but with incresed load capacity from 22 to 33 pounds) is a 12 volt-powered tangent arm star tracking platform for DSLR astrophotography. Power is supplied by either a ciggarette lighter plug or a n eight-pack of AA batteries. The AA batteries will run the mount all night. What separates the AstroTrac from most other automated star trackers is its amazing unguided accuracy. This device actually has better unguided tracking accuracy better than my Losmandy GM-8 mount. Precision polar alignment using a magnetically attached polar scope, and the extreme precision of the AstroTrac's electromicaly-driven tangent arm jack screw, allow lengthy unguided time exposures with moderate telephoto lenses without trailing of the star images. The tangent arm allows just under two hours of continuous tracking before it has to be reset. Pushbutton controls on the AstroTrac body start the tracking. When the end travel is reached almost two hours later, the device automatically shuts down. The tangent arm repidly rewinds at the touch of another button. I have taken varrying exposures ranging from 118 sequential 30-second exposures up to nine 10-minute exposures with lenses up to 135mm focal length and there is no star drift between the exposures. The device tracks perfectly. Since it does this without having to follow a guide star, passing clouds do not stop the tracking. When the cloud passes, the target is still centered and only the subframes with clouds are lost. I highly recommend the AstroTrac to anyone who enjoys widefield DSLR astrophotography with various focal length camera lenses, but does not want to tie up their telescope as a tracking platform.

The AstroTrac can be mounted on any sturdy tripod. I mount the tracker "upsidedown" on my video tripod so the pan and tilt control arm is pointed down, allowing easier polar alignment.	Under a bright urban sky, stars are difficult to see in a DSLR viewfinder. To aid in aiming the camera, I attached a Telerad finder to the camera using a bracket salvaged from an old Honnywell strobe I used back in the 1970's with 35mm film cameras.

The tangent arm on the astroTrac does not have to be aimed downward. I often use the wedge from my old C-8 to mount the AstroTrac and the wedge side braces prevent the tangent arms from aligning much lower the horizontal.	Another view of the AstroTrac attached to the C-8 wedge.

The following are various wide-field long exposure images taken with 35mm, 50mm, 85mm, and 135mm Nikkor lenses on a modified Canon 400D mounted on an AstroTrac.

My apologies for the soft edges on the 35mm lens shots, but the other lenses, especially the 85mm Nikkor, are killers! I never knew how good the 85mm lens was when I used it with film cameras. On the 400D, this lens actually rivals my old 8-inch Schmidt camera for resolving tiny stars.

The full size images have been downsized to 1500 pixels for webpage loading, and thus are about 1/4 the size of the originals.

Auriga, Canon 400D, 7x10min, ISO 400, 35mm, F/5.6 Click here for larger image

Canis Major, Canon 400D, 4x5 min, ISO 400, 35mm, F/4 Click here for full size image

Coma Berenices, Canon 400D, 9x10 min, ISO 400, 85mm, F/4 Click here for fullsize image

Comet Lulin, Canon 400D, 12x5 min, ISO 400, 200mm, F/5.6 Click here for fullsize image Click here for a small .AVI movie showing the comet's motion in just one hour.

M6 and M7, Canon 400D, 6x10min, ISO 400, 85mm, F/4 Click here for larger image

M8 and M20, Canon 400D, 4x5 min, ISO 400, 85mm, F/4 Click here for full size image

M16 and M17, Canon 400D, 6x10min, ISO 400, 85mm, F/4 Click here for larger image

A mosaic of the above three images Click here for larger image

Omega Centauri, Canon 400D, 10x5min, ISO 400, 35mm, F/4 Click here for larger image

Orion, Canon 400D, 7x5 min, ISO 400, 35mm, F/5.6 Click here for full size image

Orion, Canon 400D, 10x5 min, ISO 400, 85mm, F/4 Click here for larger image

Perseus, Canon 400D, 8x10 min, ISO 400, 35mm, F/5.6 Click here for full size image

Rho Ophiuchi, Canon 400D, 15x5 min, ISO 400, 85mm, F/4 Click here for larger image

Sagittarius, Canon 400D, 6x5 min, ISO 400, 50mm, F/4 Click here for full size image

Taurus, Canon 400D, 7x6 min, ISO 400, 35mm, F/5.6 Click here for larger image

Ursa Major, Canon 400D, 10x5 min, ISO 400, 35mm, F/4 Click here for full size image Click here for a closeup of the region near Alcor and Mizar. I was amazed to find this mushy 35mm lens actually resolved the galaxy M-101.