I've never had a Pen before and knew nothing of this non-f/stop
numbering system until I just looked it up in an Olympus Pen-FT
brochure. One of the pages covers the lenses in the system and gives
the aperture ranges of the various lenses along with their Pen "aperture
numbering system" or "through the lens number" value.
When you look at the table it quickly becomes apparent that the Pen
aperture numbers are relative rather than absolute apertures. For
example; the 38, 40 and 42mm lenses have respective apertures of 1.2-16,
1.4-16 and 1.8-16. But the Pen TTL numbers range from 0-6 for all.
Jumping around to the 400/6.3 which ranges from 6.3-32 has Pen TTL
number from 1-5. And (perhaps the clincher) the 800/8 mirror has a Pen
TTL number of 0. But strangely, although the TTL number system ranges
from 0-7 the base aperture is not always equivalent to 0. About half of
the lenses have base aperture of 0, two have base apertures of 0.5 and
the rest have base apertures of 1.
I suspect that, while the numbers are relative to the base aperture that
all are tweaked to account for some vagaries of the TTL metering system.
In the description of the numbering system it says (in a nutshell)
that TTL metering systems accuracy is influenced by position of the
meter, speed of the lens and focal length. Measured f/stops frequently
don't match proper exposure, especially at full aperture. Therefore
Olympus has designed this much more accurate system not found in other
camera systems.
So, there is no fixed definition. It's all lens relative.
Chuck Norcutt
On 3/2/2013 11:55 AM, iwert bernakiewicz wrote:
> problem is, the numbers do not directly correspond to f numbers, but the
> f numbers are exactly 180 degrees opposite of the 0-7.
> if needed i can provide data for 38 pancake, 42/1.2, 60mm (that might be an
> f only lens) and 150mm...
>
> iwert
>
> Op zaterdag 2 maart 2013 schreef John Hermanson (omtech1@xxxxxxxxxxx) het
> volgende:
>
>> Does anyone have a firm, documented list of which f stops the pen lens
>> numbers (0 - 7) correspond to?
>>
>> ___________________________________
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