TTL was a great innovation in its day. It meant the camera meter was inside
the body instead of on the exterior somewhere. The advantage was now the meter
saw what the lens saw. A fixed exterior meter always had the same field of
view, regardless of the lens used. Also, the metering cell(s) were generally
inside the pentaprism, so when the mirrow swung up, the meter was momentarily
blind.
With the innovation of OTF, all the features of TTL were retained, but the
metering cell(s) were positioned on the floor of the mirror box, pointed toward
the film. As the mirror swung up, the cells could still "see", dymanically
adjusting exposure as needed. The new cells were also fast enough to regulate
a flash, but OTF does not necessarily (although it usually does) mean auto
flash control.
Hope this helps.
John P
-----Original Message-----
From: Per Nordenberg <per.nordenberg@xxxxxxxxxx>
To: Olympus Mailing List <olympus@xxxxxxxxxxxxxxx>
Date: Tuesday, April 28, 1998 9:43 AM
Subject: [OM] TTL versus OTF
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
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