Affordable telescope mounts have small mechanical inaccuracies and not everyone achieves the perfect polar alignment. This hinders taking long exposure photos over several minutes: Stars do not appear as dots but as lines. Dark objects are invisible or appear blurry.
The solution: Agile Autoguider.
Mount your smartphone to the guider or finder scope on your telescope, calibrate the app, and start guiding. To learn how that is done, read the manual.
While guiding the app observes a so-called guide star using the back camera. A precise tracking algorithm detects when the guide star drifts away from its original position due to imprecise telescope movement.
Every time the app detects a deviation of the guide star, the app computes control commands to bring it back to its original position. This correction is either done by you (manual mode), or the app sends commands to the telescope using a WiFi-to-telescope adapter (automatic mode).
Thanks to these corrections the guide star remains in position. You can now take long exposure photos using your photocamera on the telescope that show dot-shaped star and dark objects.