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Sek-Focuser Cassegrain ASA Rotator

The Secondary Focuser is located in f9/3600mm. It is driven by a Linearaktuator L3518S1204-T6x2 motor and parallel linked to the stepper motor driver SMCI33 by Nanotec or the Amardillo controller Seletek respectively, which is ASCOM compatible. The focuser may be driven for fast movements by a selfmade controlbox in the SMC133 driver mode or by the MaxinDl software in Ascom mode.
Inside of the short extension tube/adapter and the ASA rotator, a novel removeable secondary corrector/(flattener/coma) (1x) lens (10.2cm tubediameter) has been integrated (designed by P. Keller). The corrector is fixed to the camera adapter and rotates with the camera, which leads to only one flat independet of the rotaion-degree.


The Secondary Corrector (diagram by P.Keller): These are the spot diagrams for the 2-lens corrector, which is placeable in the secondary focuser as a flattener and coma corrector. This corrector does not change the focal length. Full usable field is 80mm diameter. The backfocus is 139.57 mm measured from the center of the lensassembly. For the SBIG STX16803 the 139.57mm are reached by ( 22.6mm Center of Secondary-Corrector-Lens to the front of Rotator+38mm Rotator+13mm Adapter+33mm Filterwheel+33mm SBIG-CCD distance)

The next 3 pictures show the curvature analysis taking advantage of a secondary focuser corrected starfield picture .

Collimation test on STX16803/Corrector setup

MaximDL5.07/ASCOM control

The Seletek controller (Armadillo) is designed in order to trigger a wide varity of motors such as DC or stepper motors. For the nanotec stepper motor Linearaktuator L3518S1204-T6x2 , as used in my current setup, the innovative inventor Jaime Alemany, founder of the company Lunatico, developed also an ASCOM driver. It enables its succesfully usage by MaximDL and the Seletek Focuser Software.

Temperature correction

The controller harbors two output ports, the MAIN and the EXP and contains an internal temperature sensor. The focuser is calibrated via the Seletek (Armadillo) MAIN port, correcting the optical system. It is also linked to a second external sensor/LM60, which is itself sticked by alutape to the primary Lomo mirror in the Cassegrain.
In addition the cooling-fan of the mirror in the back of the cassegrain is triggered via the EXP port based on the measured temperature differences, in order to equilibrate the temperature gradient between mirror and environment.

Here a view to the whole Seletek (Armadillo) controller installation, with a temperature sensed mirror and correcting secondary focuser loop.

The mechanical setup of the focuser

he Armadillo controller/MAIN port and a Analog-joystick are wired to the Nanotec/SMCI33 controller. The Nanotec controller is constituted on demand in seconds by two firmware versions to a MaxinDL5/ASCOM6 or Joystick driven version. A wiring sketch is shown below on the homepage.

1.) Seletek (Armadillo) linked to Nanotec SMCI33 controller: The stepper motor is linked via the A, A/, B, B/ ports of the SMCI33, which provides enough current for heavy equipment. The direct, powerful mechanical construction enables very fine adjustable lifts of, as in the current setup, 8 kg weight. The focuser stepper motor Nanotec/ Linearaktuator L3518S1204-T6x2 is moved in microsteps of minimal (0.01mm) lenghts over the mounted thread rod Nanotec/ ZST6-2-200-1, female screw Nanotec/ LSNUT-T6X2-F. This setup had been rebuild in a very professional way by Uwe (Trulson) as shown on his homepage

2.) Joystick controller linked to Nanotec SMCI33 controller: It may be also stepless triggered to full speed by the joystick as shown below.

The joystick controller

It consist of a potentiometer (10 KOhm) and a circuit in order to generate 0-12Volt analog signals. The stepper driver in the Nanotec centroller uses the range of 0-10Volt to adjust the stepper frequenz.

The housing contains an additional red pushbutton to generate a high +12V signal flank, which itself activates the joystick motor driver SMCI33 profile.

A closeup of the PCMI33 controller linked to 12Volt power.

The nanotec controller, the different wires to stepper motor, Seletek (Armadillo) ASCOM controller and Joystick/circuit.

The following pictures show the noval ASA 4 zoll rotator. The rotator contains the secondary Keller corrector lens, which rotates together with the camera. Thereby only one Flatfield is required independet of the rotation degree at the sky.

ACC software