What does "mm" mean in camera lenses?

millimeter

You want a fish eye or wide angle lens.

I am answering the question posed in the details, since @ragingloli answered the title question; correctly even.

You will want a lens with a very short focal length. Something like 12mm. 7mm would be even better but difficult to find.
It might be easier for you to simulate the effect with Photoshop. Watch this tutorial .

mm refers to the focal length in millimeters. The longer the focal length, the greater the magnification and the narrower the field of view. For most cameras, 35 – 50mm is considered “normal”; shorter than that is considered wide angle, and the shortest are fish-eye.

The distortion is because the short focal length takes in a field of view that is much more broad than the area of the image receptor. i order to get it all on to the image, it gets distorted.

What you really ought to do if you have some interest in this topic is study the basic elements of photography. The question you’re asking is one of the most fundamental and earliest lessons of “How does a camera work?” and “What should I know about taking good photographs?”

The responses above are fine and accurate, but they’re the kinds of things that you should already know before buying equipment. (Not to criticize your question, because it’s a good one on its face, but unless you have money to waste, you should read more on the topic before you buy equipment.)

Shoot with what you have. Apply all distortions post production in Photoshop.

millimeters, with regards to lens focal length, which is the actual distance from the lens to the focal plane on the camera. It is also used to measure lens diameter, when buying and using filters.