Olympus-OM
[Top] [All Lists]

Re: [OM] Slot canyon help and low light spot metering

Subject: Re: [OM] Slot canyon help and low light spot metering
From: HI100@xxxxxxx
Date: Fri, 14 May 1999 02:40:27 EDT
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 >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz