How to Mount Large Format Lenses on DSLR Camera
Adjusting the Flange and Focusing Mechanism
Large format lenses have a long flange distance. To provide it, there are several ways. This is a special focusing helicoid. If the desired length is not enough, you can increase it by extension rings.
Dagor 150mm f/ 6,7 mounted on the camera with helicoid and extension rings
Also, this problem can be solved by bellows. I have seen such solutions in the Internet. But I like the helicoid, perhaps because I have it. Usually larger format, which accommodates the lens, have the longer flange distance. Thus, in some lenses designed to format 18x24cm flange distance is longer than 30 cm. A format 9x12 about 10 cm.
Attach the lens has to by all available means. Older lenses often have non-standard thread. There could be as savvy work. Those lenses that are small in size, I attached to the helicoid, cutting out the puck out of plastic stoppers for 20 liter bottle. In this way I was able to attach several lenses for the format 9x12 cm.
DIY mount, cork bottle, which put on the helicoid
If the diameter of the rear of the lens is large, you need to find other ways. Some lenses have to be attached with tape, as best he could not come up with.
Using a Lens Hood
I also want to note that you need to take care of the hood. It can be made from plastic tubing of suitable diameter. To reduce flare it can be cover inside black suede or matte paint, paper etc.
Lens for 9x12 cm format, with attached plastic tube, which serves as a hood. It is based on the friction force
As you can see, attach a large format lens on digital camera is simple enough. There is no need to carry out complicated operations for shortening flange. A little bit of engineering and succeed.