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GUIDING YOUR ASTROPHOTOS

The natural tendency of an astrophotographer 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 in declination, since this drift will be extremely slow. This assumes that mount was properly

polar aligned. When the star need to be reversed, it rarely takes more that 5 to 8 pulses in rapid succession, each

lasting less than 1/10 second to get the star to re-center in the reticle. This same method should be used to keep the

star centered in right ascension also. With some practice, you will be able to keep the guide star perfectly in declination

with only an occasional pulse every 5 or 10 minutes while concentrating almost entirely on the right ascension drift.

MOUNT MAINTENANCE AND ALIGNMENT

Under normal operating conditions, minimal maintenance is required. Every 12 months the clutch knobs (3 for Dec. and

3 for R.A.) should be removed and 1 or 2 drops of light oil (3-in-1 household oil) should be put in the exposed hole. If

the R.A. and Dec. axes are bolted together for a long time in outside conditions (i.e. in a permanent observatory) then

the mating surfaces should be lightly oiled or greased – if you expect to get them apart again after 10 years.

Your 1200 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, though 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. This has 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.

ASTRO-PHYSICS INC

11250 Forest Hills Road

Rockford, IL 61115

Telephone: (815) 282-1513

Fax: (815) 282-9847

www.astro-physics.com

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