Hello,
I really like the Sydney theme but am having trouble with the Header slider.
I can figure out the image size required, all the time the theme seems to stretch my images and the full image do not appear. I’ve tried from 1920 x 600 to 1920 x 1200 and nothing.
Am I missing something?
Thank you for your help. 
Hello there,
In demo, as I remember, size is 1920x1270, and you should be fine with 1920x1200px images. Can you share your page link with us so we can see what are you referring to.
Please note that since it is full screen slider, it is using HTML background-size property of cover, and default functionality is to scale the background image to be as large as possible so that the background area is completely covered by the background image. Some parts of the background image may not be in view within the background positioning area.