Quote Originally Posted by Bobf View Post

A rough equivalent with lenses is that 5x4 lenses are 3 times the focal length of 35mm ones for a similar angle of view, so the standard lens is a 150mm and the common 90mm LF lens is roughly equal to a 30mm lens on 35mm etc (it feels a bit wider than that to me, but that may just be wishful thinking on my part! ).
4X5 lenses are actually a bit wider than the "multiply 35mm by 3" rule would suggest. It has to do with the different aspect ratio of 4X5 compared with 35mm- it's not as long. A 150 is actually about equivalent to a 42 mm on 35mm, while a 90 is about eqivalent to a 25 mm on 35mm. However, due to the different aspect ratio, direct comparisons can not be made. In addition, lenses just feel wider, because of the big ground glass compared with a 35mm viewfinder.