At 1:41 pm +0200 28/4/98, Per Nordenberg wrote:
> Please excuse me for a most probably very dumb question, but could
>anyone please elaborate on the difference between the achronyms TTL and
>OTF? I think I know what they stand for, TTL meaning Through The Lens and
>OTF is Off The Film. Is that correct? Are they essentially the same
>thing? I always thought TTL was a description of light measuring during
>flash operation, i.e. light is measured through the lens instead of using
>a separate sensor in the flash itself. OTF on the other hand should be
>light measuring during auto exposure, i.e. light is measured off the film
>surface during the exposure. Is it always OTF as well when a camera is
>said to have TTL operation? Please bear with me... Per Nordenberg
Per,
TTL metering as you say is Through The Lens and is the alternative to a
hand held or camera mounted meter which measures light in the general
direction that the camera is pointed.
So TTL is used for all metering, not just flash.
OTF metering in the OM system is combined with TTL. TTL is what gives you
a reading in the viewfinder - when you open the shutter most cameras would
go with the last reading taken just before the mirror flips, the OM however
continues to meter from a light cell/s which measures reflected light from
the film plane itself - Off The Film.....
So with OTF you get the "correct" exposure even if the light levels change
whilst the shutter is open (with the camera on "auto" of course).
Good eh?
All the best,
Clive http://clive.bel-epa.com
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