Comparing 35mm and 4x5 LensesComparing Focal Lengths
There is a lot of contradictory information about comparing the focal length of a lens between different formats. It depends upon what aspect you are comparing. The one that comes most quickly to mind is angle of coverage, but that is pretty useless from a working photographers point of view. I usually convert to a fixed aspect ratio. The 8x10 print seems quite universal, so that is what I use. Then you have to figure what the size of the actual negative area you use making an 8x10 print. With 4x5 sheet film that would be 96x120 millimeters, and with 35mm film it would be 24x30 millimeters. Simple arithmetic shows you that the difference is 4:1. Therefore you can determine the comparable focal lengths by simply multiplying the focal length of your 35mm lens by 4, or dividing the focal length of your 4x5 lens by 4. For some common focal lengths in each format that gives the following:
4x5 Aspect Ratio (nominal focal lengths)
If you insist upon comparing to a 4x6 image you need to base the 35mm on 24x36mm and the 4x5 on 82x122mm. 122/36=3.4, so 3.4 is your multiplier.