Not trying to be funny but the easiest solution may be to buy an old lens ie manual focus only, which has markings. The snag is that these generally rely on a mechanical connection to the camera to stop down the aperture, which a modern camera wont have. You have to squeeze the preview button on the lens yourself.
Alternatively there are various dof calculator apps you can download. I used Photocalcs but pre calculated a number of reults to use as a ready reckoner. You will need to know your CoC value, generally taken as 0.03 for full frame, 0.045 for APSC and 0.06 for mft.
Hope.this.helps
]]>Kind Regards Ray (Manchester,England)
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