In article , Ecnerwal wrote:

Assuming you are starting from perfect (or perfectly corrected) vision
at "a long distance" (infinity, or at least the mountains across the
way) the focal length is related to diopters as the inverse in meters -
0.5 diopter will change "infinity" to 2 meters (and everything beyond 2
meters will be out of focus), 1 diopter will change "infinity" to 1
meter (and everything beyond 1 meter will be out of focus), 1.5 diopters
will change "infinity" to 0.75 meters (and everything beyond 0.75 meters
will be out of focus).

Since 0.75 meter is roughly 29.5 inches, it sounds like you should start
with a visit to an optometrist if you can't see the lathe at 22 inches
with 1.5 diopter glasses.

Your math is a bit shaky.

Focal length in meters = 1 / d, where d is the strength of the lens in
diopters. 1 / 1.5 = 0.66666..., not 0.75.

0.667 meters = 26.2"

The OP might get along just fine with 1.75- or 2.00-diopter drugstore reading
glasses.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.