This technique was trendy in 2009 and was a way to get that grungy look before Instagram became such a thing. I still love to use TTV because it's hands-on, just the right amount of challenging and very rewarding. Every photo is different and if you collect several cameras you can have a wide range of image styles. I have several cheap vintage TLR cameras purchased just for this technique and today was a test drive of my newly purchased Kodak Dualfex (the original model with the bubble top).
The method requires a DSLR with a close-focusing or micro lens and the purchase of a Twin Lens Reflex. Most cheap vintage toy TLRs like the Kodak Duaflex will do the trick. Many people purchase TLRs with dirty viewfinders for that grungy look and others select clean ones if they are only after the black frame look. The DSLR and TLR cameras are usually attached with a cardboard tube to get that nice black frame around the image. Post reduction requirements are a square crop and what ever other effects you like.
|A hand-constructed cardboard tube is all that is needed to join the two cameras. The length of the tube is determined by your lens's closet focus distance.|
|My growing collection of cheap TLRs each with a different viewfinder for effects ranging from clean to grungy.|