Focusser

Description: Create an electronic focuser to assist with astrophotography. This electronic focuser project enables precise focusing under computer control, which is particularly beneficial for eyepiece projection astrophotography. It was observed that even minor contact with the focuser could displace the object from view due to high magnification factors. The stepper motor controlling the focuser is managed by the DSC project board, utilizing spare control lines on the ports. These controls facilitate the enabling/disabling of the stepper motor and its movement in either direction at a rate dictated by the software. The control lines connect to a dedicated stepper motor interface integrated circuit (IC) to streamline the circuit. The stepper motor used for the focuser was acquired from Farnell Components, part number 7134423. This motor has a step count of 200 for a full 360 degrees of rotation, translating to 1.8 degrees of rotation per step. Refer to the data sheet for specifications. The motor operates in unipolar mode, meaning four of the eight wires connect to the +12V supply, reducing the number of wires between the focuser and the interface to five. The bracket was fabricated from a piece of aluminum, which was cut and shaped appropriately. The original focuser was disassembled and cleaned thoroughly, as the grease used was excessively sticky. Standard grease was applied instead, resulting in a smoother mechanism. The aluminum was then sized, and holes were drilled for bolting onto the focuser. The stepper motor was installed, and marks were made on the aluminum for the motor screws. After drilling these holes, the position for the five-pin DIN socket was marked and cut. The assembly was completed, and wires were soldered from the stepper motor to the five-pin DIN socket. An additional five wires were connected to a five-pin DIN plug for the stepper motor connections. To link the motor to the interface box, an old-style keyboard extension cable was repurposed; this cable is ideal as it extends or contracts as the telescope is moved. The entire focus tube travel is approximately 500 steps, allowing for quick focusing using larger steps initially, followed by smaller and then the smallest steps. Given that the distance traveled by the focuser is around 60mm, each motor step corresponds to 0.12mm. Wiring the stepper driver to allow for 400 steps per revolution could halve this to 0.06mm per step by connecting pin 10 of the UCN5804B to +5V instead of GND. The electrical tape covering the stepper motor wires is visible in the first image, while the second image shows the keyboard extension cable connected to the five-pin DIN socket on the focuser bracket. The focuser performed effectively during use. Initial focusing was achieved using the larger step command (100 steps) until the object was nearly in focus, followed by smaller steps (10 and 1) for fine-tuning. Although the weather initially cleared, it later became cloudy. However, the skies eventually cleared enough for practice shots of Jupiter. When using a 10mm eyepiece for eyepiece projection, vibrations from the stepper motor were noticeable, but the object remained well within the field of view on the screen and quickly stabilized. The focus was successfully adjusted to capture both Europa (on the left) and Io (on the right) alongside Jupiter.

The electronic focuser system comprises several critical components, including a stepper motor, a control interface, and a mechanical assembly designed to hold the motor and telescope securely. The stepper motor, specifically the model acquired from Farnell, has been selected for its reliability and precision, with a defined step count that allows for accurate adjustments in focusing. The unipolar configuration of the motor reduces complexity in wiring and enhances the overall robustness of the system.

The DSC project board serves as the central control unit, interfacing with the motor through a dedicated IC that simplifies signal management. This configuration allows for precise control of the motor's direction and speed, enabling the user to achieve fine focus adjustments that are crucial for astrophotography. The software used to control the motor can be programmed to send commands for varying step sizes, facilitating both rapid and precise focusing.

The mechanical assembly, constructed from aluminum, provides a sturdy platform for the motor and ensures that the focuser remains stable during operation. The choice of materials and design minimizes unwanted vibrations that could affect image quality during photography. The five-pin DIN socket allows for easy connection and disconnection of the motor, while the keyboard extension cable offers flexibility in movement, accommodating the telescope's positioning.

Overall, this electronic focuser is a valuable addition to any astrophotography setup, providing enhanced control and precision that significantly improves the quality of captured images. The careful selection of components and thoughtful design considerations contribute to the system's effectiveness and reliability in demanding photographic conditions.Make an electronic focuser to help with the astro-photography. The electronic focuser project allows accurate focussing under computer control. This is most useful for eyepiece projection astro-photography where I found that touching the focuser was enough to knock the object from view, because of the higher magnification factors involved. The stepper motor for the focuser is controlled by the DSC project board, using spare control lines on the ports. These controls allow the stepper motor to be enabled/disabled and moved in either direction at a rate determined by the software. These control lines are connected to a dedicated stepper motor interface IC to simplify the circuit. The stepper motor for the focuser was purchased from Farnell Components part no 7134423. The motor has a step count of 200 for 360 degrees of rotation which equates to 1. 8 degrees of rotation per step. Check out the data sheet. The motor is configured in unipolar mode, which means that four of the eight wires are connected to the +12V supply, and brings the number of wires between the focuser and the interface down to five.

The bracket itself was made from a piece of aluminium I had lying around and it was simply cut it to size and shaped. The original focuser was first stripped down and thoroughly cleaned as the grease used was of a very `sticky` type.

I then used normal grease instead which made the mechanism much smoother to use. Next the aluminium was made to size and holes drilled to allow it to be bolted on to the focuser. The stepper motor was then fitted and marks made on the aluminium for the motor screws. After these holes were drilled, the position of the five pin DIN socket was marked out and cut. Finally the whole thing was assembled and the wires soldered from the stepper motor to the five pin DIN socket as in the picture below. Another five wires were connected to a five pin DIN plug for the stepper motor connections (the wires in the picture above).

To connect the motor to the interface box I found an old style keyboard extension cable made from coiled wire. This was ideal as when the telescope is moved the cable simply extends or contracts accordingly. The full range of the focus tube, from one end to the other, is in the order of 500 steps so focusing can be quickly achieved using the larger steps first followed by the smaller step and finally the smallest step.

Since the distance travelled by the focuser, from end to end, is around 60mm this means that each step of the motor is equivalent to 0. 12mm. I could have wired the stepper driver to allow 400 steps per revolution which would have halved this figure to 0.

06mm per step! If you wanted to do this simply connect pin 10 of the UCN5804B to +5V instead of GND. In the first picture note the electrical tape covering the stepper motor wires. In the second photo the keyboard extension cable can be seen connected to the 5 pin DIN socket on the focuser bracket. In use the focuser seemed to work very well. Initial focusing was done using the larger step command (100 steps) until the object was near to focus.

The smaller steps (10 and 1) were then used to sharpen the picture as much as possible. As expected the weather was clear when I started to set up and then decided to cloud over a bit later. I persisted and later the skies cleared enough to get in some practice shots of Jupiter. I found that when using a 10mm eyepiece for eyepiece projection, the vibration caused by the stepper motor was visible but the object was still kept well in the field of view on the screen and settled down very quickly once again.

In this photo of Jupiter I managed to focus on both Europa (on the left) and Io (on the right) as well as the planet itself. By movin