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GUIDING YOUR ASTROPHOTOS

The natural tendency of astrophotographers is to push the directional button of the controller in the direction he or she

wants the guide star to move until the star has centered itself in the guiding reticle. This method often results in

overshooting the center of the reticle since the reaction time to let go of the button is often too late. By the time the

gears in the drive motor have reversed and are driving again at the normal guiding rate, the star has moved past the

center of the reticle. Then the opposite button is pushed to move the guide star back in the opposite direction toward

the center and the same overshooting may occur.

The proper way to guide (and this will apply to almost any commercially available mounting) is to pulse your

correction, much like the SBIG ST-4 does in its auto-guiding operation. Pulse the button for only a fraction of a

second and note the new position of the guide star. If it has not moved far enough, pulse it again. Normally, it takes

only one or two pulses to re-center the star. Declination drift can be eliminated by proper polar alignment. Fine

adjustment can be made by noting the direction of Dec. drift and, using the azimuth adjusting screws, by moving the

star in the opposite direction. Several of these iterations can be made until the Dec. drift is in the opposite direction.

R.A. drift will occur if the polar altitude is set wrong. If the drive rate seems to be too fast (star drifts eastward), the

altitude is set too low. Adjust it upwards until the R.A. drift stops or reverses. Both altitude and azimuth will affect

each drift rate, so some back and forth adjustment may be necessary.

MOUNT MAINTENANCE AND ALIGNMENT

Under normal operating conditions, no maintenance is required. Your 400QMD is a precision instrument with very

accurate worm and wheel adjustments. Please be careful if you place the mount on a flat surface, i.e. the ground or

trunk of your car. The gear alignment may be affected if the R.A. and Dec. motor/gear box assemblies sustain undue

lateral force. This is true of any fine instrument. We suggest that you transport and store the mount in a case or in a

well-padded box

NOTE: If your battery runs low, the declination motors will stop first, through the R.A. will continue to drive until

the power is drained.

If any problems occur, please don't hesitate to contact Astro-Physics for assistance.

Recommended reading list from our staff:

The Backyard Astronomer's Guide, Terence Dickinson and Alan Dyer, Camden House Publishing, 1991. The authors,

both former editors of Astronomy magazine, offer practical insight into astronomical equipment, finding your way around

the sky, polar alignment, using setting circles, and astrophotography. This book provides excellent explanations and is

well organized and illustrated.

All About Telescopes, Sam Brown, Edmund Scientific Company, 1975. Excellent information regarding the principles of

mount construction and operation, using setting circles, eyepiece projection, etc. Illustrations and formulas galore. Many

of the instruments pictured are outdated, however the underlying principles are timeless.

Norton's 2000.0 Star Atlas and Reference Handbook, edited by Ian Ridpath, J. Wiley Publishers, 1989. Star maps,

information regarding polar alignment of German equatorials and observing techniques.

04-25-95

ASTRO-PHYSICS INC

11250 Forest Hills Road

Rockford, IL 61115

Telephone: (815) 282-1513

Fax: (815) 282-9847