This Mount Helps Photographers Track Stars in the Night Sky
Getting that perfect image of somewhat faint stars uses a technique called stacking, and this mount can accurately assist in the process.
Image stacking
In the field of photography, there are three primary values that go into a digital photograph: shutter speed, ISO, and aperture size. Most people are probably familiar with the fact that images tend to get grainy/noisy the darker it gets, and that is because the ISO, or sensitivity to light, must be increased as the amount of light available to the camera's sensor goes down. Although this can be compensated for partially when the subject is clearly defined, it is detrimental whenever the camera is pointed into space since faraway stars appear like grainy blobs. One approach is to increase the exposure time, but it also means that things can get fuzzy as the Earth rotates. This is why astrophotographers often reach for an alternative: stacking.
Stacking is a technique in photography that combines a large series of images pointed at the same subject by averaging their values together in the hope of reducing the overall noise and increasing the signal-to-noise ratio. Unlike on the ground, the object in the sky still needs to be tracked in order to compensate for the Earth's rotation, and Jhilam has created a DIY project that does exactly this.
Designing the mount
His intelligent EQ mount star tracking system contains a single NEMA17 stepper motor with a 1:100 planetary gearbox attached for increased resolution and torque. This motor, in turn, fits into a small enclosure that has a set of two helically cut gears that convert the rotation from the planetary gearbox into a much slower sweeping movement. The entire body and gears are all constructed from 3D-printed plastic components.
The circuit and PCB
In order to consolidate space in the somewhat restricted size of the mount, Jhilam designed a custom PCB that slots onto a Raspberry Pi 4B's 40-pin GPIO header. One set of signals head to an A4988 stepper motor driver module that controls the stepper motor's rotation based on the number of pulses going into its step pin. The back of the board has a header for an IR receiver that can get commands from a remote control, and the front has an OLED screen that shows the current speed and direction.
Using the system
To capture images, the user first powers on the Raspberry Pi 4B and launches the program. From here, the user can set the rotational speed to match the Earth's for a given latitude and then start the sequence with the IR remote control. The camera at the top then captures an image once every few seconds for later combination in a photo stacking application. To see this star tracking mount in action, you can watch its demonstration video here on YouTube.