K3's AstroPhotography
"When I consider your heavens, the work of your fingers, the moon and the stars which You have set in place, what is Man that You are mindful of him?" -- Psalm 8:3,4

Homemade Electronic Focuser (EF)

Astrophotography requires a precise focusing. This can be achieved by using electric focuser - motor driven focuser. Manual focus is not as fine as motorized focusing. Furthermore after manual adjustment of focuser the telescope and mount need some time for damping vibrations.

So I started a new home-made project - Electric Focuser - together with my very good friend - Jan Timmermans. He inspired me and helped me to obtain parts for focuser. So the final product is a result of our cooperation. Jan prepared very nice Step by Step Progress Report (application of EF for TAL telescope).
The original idea of electric focuser comes from Rudi Prinz: http://home.foni.net/~quante/teleskope/tal/taltips/tfk/tfk.htm.

The motor is fixed to aluminium plate by means of blue aluminium belt (with rubber plate). The motor plate is fixed to focuser by means blue aluminium belt (with rubber plate) - around the focuser. The gear wheel is fixed to focuser knob with M4 bolt (a wing nut is used for allowing manual focusing - by loosening it).

Parts List:

The electromechanical parts were ordered from CONRAD Electronics. (the order numbers are Conrad order numbers).

Part description Order number Pieces
Motor, 12V, 120 rpm (gearbox reduction: 1:50) 227552 1
Wormwheel + cogwheel (= with teeth)1:30 236900 1
Motor polarity switch relay 12V 505013 1
Plastic case for control unit 541214 1

Electronic parts:

Designator Part description Part type Pieces
T1, T2 Transistor NPN BC546A 2
R1, R2 Resistor (0.25W) 3k9 2
ISO1, ISO2 Opto-insulator PC817B 2
D1, D2, D4-D7 Diode 1N4148 2
D3 Zener Diode BZX85V006.2 1
C1 Capacitor electrolytic 220uF/16V 1
C2 Capacitor ceramic 100nF 1
C3 Capacitor rolled 100nF/100V 1
SW1, SW2 Push button   2
J1 MiniJack 2.5mm socket   1

Construction Photos:

Here are photos of my beta version of electric focuser:

Motor plate mounted on focuser

Worm gear and gear wheel detail

Mounting of motor plate with blue aluminium belt

Another view of aluminium belt.

Relay and push-buttons for controlling the motor.
(Sparrow nest construction...)

The focuser control electronic.

The control unit - UP / DOWN pushbuttons
and NORMAL / SLOW switch

The computer control interface - 2.5mm minijack socket.

The full version of schematic
(with computer interface)
Click the image to see full size.

The PCB. The blue lines are paths on PCB, the red lines designate wiring.

The simple version of schematic
(without computer interface)
Click the image to see full size.

Wiring diagram of simple version

The first test object of EF was Albireo.

Step by Step Progress Report (application of EF for TAL telescope) / Jan Timmermans/

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Last Update: 10.12.2001