In a message dated 5/13/99 9:09:22 AM Pacific Daylight Time,
jowilcox@xxxxxxxxxxxxxxxxxxx writes:
Tim,
Would you be able to translate this somewhat more into "working terms"?
For instance, what's the maximum exposure in auto at f16?
Thanks, Joel >>
=====
Joel ,
Here is a handy url for easy look up and explanation of EV values:
http://www.hyperzine.com/evtable.html
but the site only shows values down to -1 EV although you can obviously
continue the series down lower yourself.
However the OM2N service manual lists some extreme values as well as the EV's
so here is the complete quoted spec (including weasel words ) from Olympus:
"Measuring range : ASA 100 from F1.2, 120seconds to F16,1/1000sec. (EV-6.5 -
EV18) (at normal temperature and humidity)"
The "normal temperature and humidity" refers to the fact that circuit leakage
limits the accuracy at these extreme low currents from the silicon
photo-diode sensors. In particular they have to use special low leakage
boards, a matched mosfet pre-amplifier and extreme cleanliness. High
temperature and or high humidty will cause errors through surface leakage at
low light.
The OM2N service manual also compares the old OM2 exposure shutoff limit to
the improved 2N limit with about two pages of detailed description. The old
OM2 had a much more variable exposure limiter which could get limits from a
minimum of 2min to as long as 20minutes, while the 2N has a limit "a few
seconds" over 2min according to one diagram. But elsewhere they say there is
no possibility of it getting over 5min. My translation: they hope for a few
seconds over 2min but worst case you might get as long a total time as 5min.
Interestingly you could easily switch off the limit circuit to get
really long auto exposures if you then used an external battery pack to stop
the batteries being killed by the long continuous battery drain. The accuracy
will ultimately be limited by circuit leakages and you might have to clean
your boards with some freon or noxious solvent. On the other hand it is
fairly easy to test the limits of your particular camera by adding some ND
filters and checking that the exposure times double etc with a stop watch.
Tim Hughes
Hi100@xxxxxxx
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|