Depth of Field Slide Ruler for Photographers

Among several other aspects, the medium format (6x6, 6x7...) itself has one big advantage over smaller formats.  The photographer can put a considerable emphasis on a subject by working with the very small depth of field aperture settings.  If you follow that line, you better know your lenses.  The Mamiya RZ lenses have a lever that can stop down to the preferred aperture and visually check the DOF, however, that does not always help due to the darkness of the focusing screen when you close the aperture. The Mamiya lenses also have a little slide ring that can be adjusted (aperture/distance) that show the DOF,  but it is relatively coarse.  So it's always better to know in advance what you can expect from your lens, and swap them if necessary.  There are three main aspects of depth of field that I try to keep in mind for the main lenses I use:

- hyperfocal distances (min, medium, max aperture)
- DOF at open aperture at 5 meter focus.  The 110mm/f2.8 has a DOF of around 140cm here.     
- DOF at open aperture with an extended focusing bellows at around 4.5ft / 1.5meters distance (typical close up).  At that distance the DOF with the 110mm/f:2.8 is only a few centimeters, around +- 6cm!   

Now, for my working horse lens, the 110mm f:2.8 lens I have these values pretty much memorized. This is a great lens and but has to be respected because of it's shallow DOF capabilities.  But what if you need precision?  What about the other fixed focus lenses?  
I tried to use smart phone DOF calculators, but gave up on them.  Too hard to read on bright sunny days, and I loath fumbling around with the phone while photographing.  I tried to print charts, but they only gave hyperfocal values.  Important enough, but the object distance is equally important, if not more.     A few days ago I found a slide rule type calculator on the net, which is pretty nifty and also works for other formats than 6x7, from 35mm up to 8x10 large format.        

For those who are interested, here it is:
nomographics.com/web/resources…

Now I have to figure out how to put it together in a sensible way


Best,
Mark