The main character in my film is someone who is trying hard to focus on pleasant memories but whose mind is continually invaded by negative ones. The character never speaks, so lens whacking is one way in which I saw fit to translate his psychology visually. The film's aesthetic is based around light and it's relationship metaphorically to memory, so this also made the effect well suited. 

By detaching the lens and moving it back and forth in front of the sensor, focus can be shifted rapidly from a slight depth of field to deep focus, and light leaks in natural, smooth streaks and washes onto the sensor. Additionally, we also chose to flag around the backend of the lens to have more control over the light and distorted the image by twisting the lens away from the sensor at an angle. A lot of cameras nowadays can shoot without a lens, particularly DSLR's, but we were using a Panasonic AF101E which doesn't, necessitating taping down the contacts to fool the camera. What was achieved by DoP Garry Torrance can be seen below.

There's many examples of rough-and-ready cinematography. Ben Wheatley's A Field in England used a Holga toy camera and cheap telescope glass to create a fantastic otherworldly atmosphere (watch their behind-the-scenes video here). The hard-to-find Another Girl, Another Planet by Michael Almereyda, a favourite of mine ever since I bought it on a whim from a Global Video bargain bin years ago, used a Fisher Price Pixelvision camera, which records on standard cassette audio tapes and renders everything in a shimmering lo-fi somewhere below corner shop CCTV in quality. You could call it a gimmick, but obfuscation becomes viewer engagement and peering into Almereyda's ghostly murk feels immersive and dreamlike for me in a way no film apart from Primer has since accomplished.

UPDATE: I've uploaded my VHS copy of Another Girl Another Planet here

I'd love to find more examples, or hear stories from other filmmakers who have dabbled in weird techniques and risked breaking their equipment for the sake of a film, so please comment below.