Basically, you get an old camera, the older and grungier the better - and you confound everyone by sticking your brand new digital camera into it, to get amazing and unique images... but why bother?
Well, most cameras now are so easy to use, they do everything for you, and as with most automated functions, there comes a distinct air of uniformity... all images will conform to the strict abilities inherent in your camera, as it will work out all the hard stuff (framing/shake/focusing) for you.
Using an old camera, with unpredictable image quality and varying degrees of light coming through, kind of shakes that up a little and achieves distinctly unique images.
Also the images are bloody amazing... I use a 50 year old Kodak Brownie Reflex camera, made of tin and bakelite (although my previous "Through The Viewfinder" camera was a Lubitel), which comes with plenty of lens fluff (the black stuff that flakes off the inner camera workings) and distortion around the edges. The results of using this concept are that I can take very authentic-looking vintage photographs, with all the flaws and mistakes that we associate with old photos, but with high colour tonality thanks to digital imaging.
Ok - I attach a light, tight cardboard tube to the top of the older camera's viewfinder, with a bug magnifier facing down into the camera (to boost the macro on my digital camera), wrap it all up in duct-tape, and spend a few evenings getting the framing inside the tube just right (this bit takes a while, you have to have the right length of tube and the inner bug lens has to be placed at the correct distance between the two).
But any set-up will do, it depends on the camera that you use to record the image. Then you look for a suitable good image with plenty of colour and atmosphere (such as a fairground slide, or rusting old trams), and wiggle the cameras around until the image is what you want. This is the tricky bit of "Through The Viewfinder" - you are juggling TWO cameras at once. As if one wasn't bad enough, you are dealing with a very old one and a new one trying to harmonise them both!
Once taken, I usually Photoshop the image and saturate the colour and contrast, but basically I'm looking at photos from the 50's and trying to get that same washed-out or heightened colour that they had then. It depends on the image - so a little control comes in here!
I just like using old cameras really....
You can find a full "how to" here: www.russmorris.com/ttv