I have a cheapish fish-eye lens suitable for my crop-format digital camera. So, not being able to afford a full-format camera, I took the opportunity of using my film camera to see what the full image looks like:
This first image shows the garden with the lens hood still in place. I have cropped off the excess black from around the outside. The shape of the lens hood is mostly visible in the centre of the top and bottom edges. The lens hood is designed with crop format sensors in mind.
And this is the same view with the hood removed:
This shows clearly the image circle. Cropping off the black has just been at the sides, so the circle is truncated top and bottom by the film format. You can see the image extends just a bit more all the way round.
Here is another pair of photos both with and without the hood:
As the sun is in the view, you can see reflections in the lens hood of the first of these two photos, as well as lens flare.
Overall, comparing the cropping by the lens hood with the full image circle, I don’t think I am missing much at the edges. So I wont buy a full format digital camera just to get the circular image…