I use a wehman 8x10 and carry a 4x5 back as well. I don't get as much rise as i'd like with my 90mm but it's fine in nearly all cases. Making blanks to accomodate other backs is easy with this camera as i uses 1/4" material.
The Wisner 8 x 10 will focus to 90 mm on the normal bellows...it will go to 40 mm with the bag bellows...I like the Wisner cameras because I can use the longer lenses and for its rigidity when extended..IMNSHO it is the best camera offering the most features and stability---the tech series has great movement ability..
The 8x10 Rochester Universal I just acquired has inserts for it's plate holders that allow for 4x5, 5x7 and 6.5x8.5. The ground glass is marked for each of these formats as well. I had 4x5 film holders that fit and I can "reassign" some of my 5x7 film sheaths, but I'm going to have to works some to do the full plate thing - maybe use Ole's jam on glass routine? Have to cut the film down too...
On second thought, maybe I better get used to the single format first. I tend to experiment too much as it is. I think less is more here.
I see my name popped up in this discussion, too...
My 24x30cm plate camera has three holders with format reducing inserts to 18x24cm, 13x18cm, 10x15cm, 9x12cm, and 6.5x9cm. Other inserts ahould be fairly easy to make. The camera can also focus a 50mm lens at infinity. With rise/fall and shift on the lens board, there is no need for bag bellows. I won't get much swing or tilt with the shortest lenses, but then again it doesn't take all that much with such short lenses...
Are you taking this camera into the field? In the studio, I think it's reasonable to use an 8x10" or larger camera with reducing backs, but in the field, I can't imagine carrying an 8x10" camera and requisite tripod just to shoot 4x5", and since some 4x5" cameras (like the Deardorff 4x5" Special) are really just 5x7" cameras with reducing backs, it makes sense to combine those formats, if you are using reducing backs.
Of course the Sinar and Arca-Swiss change the rear standard frame and bellows, so this is a different approach than using reducing backs, but it's also more like owning several different cameras, since only the rail and front standard are shared by the different formats.
I have to agree with David. If you're going to schlep an 8x10 camera into the field, why would you want to put a 4x5 back on it? Instead of a 90mm lens with a 4x5 back, wouldn't you be better off to replace that 90mm lens with a 180mm wide angle lens and always shoot 8x10?
Colour 4x5 film is more common and cheaper. Not to mention enlargers. Or you may want to stick a roll film holder on the camera.
Most of the reasons to use a smaller camera apply to reducing backs. I've got 5x7 and 4x10 backs. Plus a 6x17 roll film back. I could crop all three out of a sheet of 8x10 but it doesn't take much film to cover the cost of the reducing back and holders.