Canon EOS 850D Advanced User Guide

To perform a factory reset, go to the Menu, select the 'Wrench' icon, then choose 'Clear settings'. Confirm by selecting 'OK'.
Ensure the battery is charged and inserted correctly. Check the battery compartment and contacts for any debris. If it still won't turn on, try using a different battery.
Download the latest firmware from the Canon website, transfer it to an SD card, insert the card into the camera, and run the update from the 'Firmware' option in the Menu.
Ensure the lens is set to AF mode. Check for any dirt on the lens or sensor. Also, verify that the shutter speed is appropriate for your shooting conditions.
Use the Canon Camera Connect app. Enable Wi-Fi on the camera, connect your smartphone to the camera's network, and follow the app instructions to transfer photos.
Use a blower to remove loose dust. For stubborn spots, use a sensor cleaning swab and solution. Always follow the manufacturer's guidelines to avoid damage.
Reduce the use of the LCD screen, lower the screen brightness, turn off Wi-Fi when not needed, and use the camera's 'Eco Mode' if available.
Turn off the camera, remove the battery, wait a few seconds, and reinsert the battery. If the error persists, consult the user manual for specific error codes and solutions.
Use a wide aperture (small f-number) and position your subject far from the background. A lens with a long focal length can also help achieve a shallow depth of field.
Adjust your camera settings to your preference, go to the Menu, select 'Custom shooting mode (C1, C2)', and save your current settings.