The lightest 645 ever made? I guess that would be a
holga Is 140g light enough? of course then you have to put on 200g of tape and glue to combat the light leaks... :rolleyes:
I would broaden the search to 6x6 folders. I would consider maybe one of the Agfa Isolettes, or maybe one of the Zeiss Ikontas. Or maybe one of the original mamiya-6 folders. There are a whole bunch of 120/220 folders. There seems to be a pretty good list here...
http://www.pibweb.com/ross/Campix/folders.htm
Sandy is right though, if you are looking for a modern,
non-folder 645, the fixed-lens Fujis are the probably lightest. Some of the models aren't exactly compact, but they are light and
lots of fun. Nice thing about them: they are vertical (portrait orientation) 645s. Some people say they are plasticky, but actually they are very well built and can take some hard knocks.
P.S. I am a big proponent of the mamiya 6 (the modern one) and the body + lens weighs in a just over a kilo... comparable to a Nikon F100 + lens, if that says anything to you. And a 3-lens 6 kit is actually more compact than a typical F100 kit.
P.P.S. The lightest 645
slr that I possess is the mamiya 645 pro, which is considerably lighter than the pentax 645N, IIRC. But there are probably some slightly lighter ones.