What type of fisheye lens do I need?

I've got a Nikon D5100 with the stock 18 to 55mm lens. Basically what I'm wanting is the peephole effect, you know where its like a round image that looks like you are looking through a peephole, and it's kind of like a bubble effect. I want one of the lenses that just screws onto the current lens that I have, but all the fisheye lenses I find are for far away wide angle photos, I want the bubble effect, not a long wide angle. How do I achieve this and what lens do I need?

Added (1). Okay but how do I adjust the camera to where the shot is in a circle instead of a rectangle, do I need to zoom way out, or adjust the settings of the camera?

You need no lens, you can screw a narrow hood

The two effects are the same. As long as the person stands close to the lens, you should get the bubble effect.

Here is what a true full fisheye sees.

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As you can see, you have to be aware of those standing next to you, the shadows being cast and your own feet when taking such a shot.

As far as finding a 180 degree full circle lens for your D5100, good luck. All the current fisheye lenses for APS-C cameras fill the frame the the 180 degree visual is only from the diagonal corner to corner.

The only fisheye lens I have seen that will give a true 180 degree full circle is a Sigma 8 mm lens mounted on a full frame camera like the Nikon D600. That lens costs in excess of $800.

That being said, those $40 screw-on fisheye filters might work, but you will have to buy one that is something like a 0.25x to get a full circle view. You will need to make sure that the filter thread size is the same are your lens, mainly 52 mm