In article 2017051115282110289-savageduck1@REMOVESPAMmecom, Savageduck
says...
However,
there are times when the camera metering will fail you, or there is
little choice but to go full manual and the assistance of a good
incident/spot light is going to be invaluable. Consider shooting in a
studio with variable artificial lighting, or outdoors using ND filters.

Not sure I understand why you would need an external metering device in
such cases. Can't you just take the shot and if it comes over- or
underexposed, simply adjust the exposure and retake the shot?
--
Alfred Molon

Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site