There have been a couple of interesting threads lately on gear and technique that devolve into discussions of accuracy and precision.

One had to do with the potential for focus shift when stopping down. Another revolved around the quality and precision of spirit levels used in LF photography.

some responses on these threads involved discussions of precision in alignment and leveling that only a machinist would worry about. Which brings up a question in my mind: How much precision and accuracy is enough? Alignment and plumbnb-ness are just two parameters of what we do though.

So just how accurate are shutter speeds? A speed of 1/500th should equal 2 mili secs. Setting 1/250th should be 4 mili sec and 1/125th ought to be 8 mili sec if I have counted on my fingers correctly. A half sec should be 500 mili sec.

So how close is close enough? Is plus-or-minus 10% acceptable? Do we even get +/_ 10%? What should we expect as to accuracy and reputability (precision) from a new-ish Copal shutter? How many sequential tripps of a shutter come how close to the nominally set speed? What about older designs; Compur, Alphax, etc. ?

What about Lightmeters?

What about aperture settings or focal length? How close are the markings to acrtual and how close do we need them to be?