I Want To Recommend Getting A Nikon 90 mm f 8.0
One issue with 90 mm lenses, is that most modern lenses require a center filter, to get the correct exposure, across the frame. One that doesn't, which was my pick, is the Nikon 90 mm f 8.0. The f 5.6, is too big, too heavy & has too much lens in the rear, for a box camera. When you examine how many elements / groups each 90 mm, ( slow ), lens has, you see, that the Nikon, has 1 - 2 more elements.
The 6.8, would fit into the slow category. That is the basic design of the slow lenses, is one where, almost all of the lens elements are in front of the lens board. The faster lenses are symmetrical designs, where there are an equal # of lens groups behind the lens mount as there are in front.
There is no room for this design in a Graphic.