1. choose the eliptical tool, hold down shift and drag over the area where you want the picture to have the effect. (holding down shift only makes the circle an even circle when you drag it. you dont have to hold down shift but it helps it look more realistic)
2. on your top bar go to select and choose inverse (make sure your foreground color is black)
3. after you do that then press the delete button on your keyboard
4. once you have done that then use your paint bucket tool and paint the free space black
5. once again go to select and then inverse
6. after that go to filter which is on your top bar and go to distort and off of that choose spherize (keep it at 100% and normal)
7. go to the select bar and then choose deselect
boom your done. very simple stuff. post your pictures that you used this effect on.