Hi Al.
It's not a circular image with a crop sensor camera. I'm not sure about full frame as I don't own one and have never used it on one. The lens was designed for the crop sensor mirrorless Sony/NEX cameras, either a 1.5x - 1.6x crop factor, should work fine on 4/3rd sensors too like the Lumix with a lens adapter to fit the camera mount but do your research first before using it on another crop sensor cameras for other than Sony E mount.
It could be used for an all sky lens with your camera pointed at zenith.
Here's a few examples that I could find quickly. Keep in mind I'm no expert at photography
I bought it for astro work, mainly for capturing meteors and have only used it sparingly on the odd occasion. I didn't even try it for daylight photography. It's one of those things that we all buy and it then spends most of it's life packed away in the box.
https://s31.postimg.cc/qx5wc77pn/DSC...w_Norcia_2.jpg
https://s31.postimg.cc/vkgjrqn17/DSC..._July_2017.jpg
https://s31.postimg.cc/ctemhvi9n/DSC..._Milky_Way.jpg