Just started trying to engrave photos on slate coasters. Results coming out virtually one medium shade of grey and cannot see any detail as no shades of dark grey to white shown.

Photo has been converted to greyscale and inverted.

Have left Power (30%) and Speed (180mm/s) settings default. 

I guess it's the ‘Adjustments’, ‘Power’ and ‘Speed’ settings issue?

Any help appreciated. Thanks.