David Nebenzahl writes:

One question: are you sure of the spelling of this item (Da Yi)? I Googled for
it unsuccessfully. Either it's spelled [spelt] differently, or it's one of the
best-kept photographic secrets on the Internet.

From Peter's excellent description and review it sounds as if this
may be the same back as the Shen Hao sold by Robert White in the UK.
The description at

http://www.robertwhite.co.uk/shenhao.htm#Label617

has photos of the back, and says the longest lens you can use without
vignetting is 150mm.