I had a Super Angulon 90mm F/8 and it was a little tough to focus, but it worked out fine for me. Having good ground glass or a fresnel lens on the ground glass definitely helps. Sometimes the original ground glass that comes with these cameras is not the brightest. The faster wide angle lenses are easier top focus, and a lot harder to carry and more expensive to buy. For field work, I would personally trade the brightness for the weight and cost of the faster wide angle lenses.

Have fun!