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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
:iconnigel-kell:
Nigel-Kell Featured By Owner Sep 1, 2016  Hobbyist Photographer
A cunning design! Though probably rather complicated to make. I do like slide rules; and use them (much to the dismay of offspring). This would be a fun thing to produce out of the bag, even if most of my lenses have engraved DOF markings!
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:iconroger-wilco-66:
Roger-Wilco-66 Featured By Owner Sep 1, 2016   Photographer
I also love slide rules!  It's the same like working with analog photography.   Using them get's you much more involved in the process, and it generates a deeper understanding of what you are actually doing.  My flight trainer always said that and made us use the Aristo Aviat (an E6B type computer) instead of hand held electronic navigation computers.  He was absolutely right!  You immediately know that somethings wrong when you dial in a wrong parameter or make a wrong setting.   

I ordered 1mm PVC sheets that can be cut with a good scissor.  Then I plan to print the ruler on a white adhesive inkjet foil which will be applied to the pvc parts. Should work!

I guess after using it a while one doesn't need it anymore for the standard lenses because the rough data is memorized.      
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:iconpearwood:
pearwood Featured By Owner Aug 31, 2016  Hobbyist Photographer
Cool. Most of my cameras have the DOF indicator built into the focus knob, which is helpful. The Weltur has it printed on top.
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