--=_Listar-UnMime-Boundary
Content-Type: text
Moose,
I meant the "front element opening" being the filter thread size
diameter.
You are correct in stating that Olympus calculated those maximum
f-stop aperture values based on their knowledge of the actual lens
characteristics.
I intentionally did not want to use the term 'filter thread size', but
wanted to loosely point out the relationship between the max f-stop
versus the physical diameter of the front element lens openings.
The 180/2.0, 250/2.0, and 350/2.8 have much larger front element
diameter compared to the rest, and therefore, no stepping down of
the max f-stop.
Sorry to confuse you or mislead other folks on the list. I thought
I was serving the List members when I first saw Skip Williams' post on
the subject and decided to translate and share the information during
off-work hours. If you think I do lousy translation, then I will
shut up.
Jim Terazawa
-----Original Message-----
From: Moose <olymoose@xxxxxxxxxxxx>
To: olympus@xxxxxxxxxx <olympus@xxxxxxxxxx>
Date: Tuesday, January 20, 2004 8:38 PM
Subject: [OM] Re: Free OM-to-E-System adapter - Update2
>
>I don't know what the column "Front Element opening diameter" is
>aupposed to mean, but it isn't what it is labeled. It is the filter
>thread size, which bears only a vague relationship to the actual clear
>diameter of the front element. For a simple example, the clear diameter
>for the 85/2 is about 42.5mm while that for the 50/1.8 is about 28mm,
>although they both use 49m filters. This is simple math (85/2 = 42.5,
>50/1.8 = 27.8) confirmed by measurement.
>
>I suspect there is no logic that will work from this data. Oly likely
>calculated the angle of incidence of light at the corners of the 35mm
>frame from their knowledge of the actual lens characteristics. Thus the
>200/5 doesn't require stopping down at all, while the 200/4 requires
>stopping down to f8 (2 stops, rather than the 1 noted in the table.).
>This indicates that the 2 lenses, although of the same focal length and
>less than 1 stop different in speed, are optically quite different.
>
>Moose
>
--=_Listar-UnMime-Boundary--
The olympus mailinglist olympus@xxxxxxxxxx
To unsubscribe: mailto:olympus-request@xxxxxxxxxx?subject=unsubscribe
To contact the list admins: mailto:olympusadmins@xxxxxxxxxx?subject="Olympus
List Problem"
|