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Re: [OM] Infrared Marking (Was 35-70 F/3.5-4.5 formula)

Subject: Re: [OM] Infrared Marking (Was 35-70 F/3.5-4.5 formula)
From: Tomoko Yamamoto <tomokoy@xxxxxxxxx>
Date: Wed, 04 Feb 1998 13:04:15 -0800
At 04:58 PM 2/4/98 +0100, Marco wrote:
>Every lens focuses different wavelenghts light at different distances (that
>is called axial chromatic aberration). In common lenses, exp. long lenses,
>there is a considerable gap between blue and green from one side and red to
>the other. So most lenses have a red dot on the barrel in order to correct
>focus when using infrared or b&w red filters. It is a reference for the red
>focusing plane. 87 filter cannot correct focus, the fact is this: that red
>focuses on a different plane that other colours. Some lenses have not red
>dots because are corrected for all the three colours, that is are APO
>lenses. 
>
>btw: all my prime lenses have a red dot, while no zoom lens has...
>
I checked my collection of Zuiko lenses.  The ones with a red dot for IR are

135mm/3.5
35mm/2.8 shift
200mm/5

The ones without are:

50mm/1.8 (Mine is an M-system lens that came with my M-1)
28mm/2.8
35-70mm/3.5-4.5
35-70mm/3.5-4.8 (latest zoom)
100mm/2.8

If I remember correctly, the latest zoom 70-210mm/4.5-5.6 has an infrared
mark.


Tomoko Yamamoto
Photographer, Composer, Soprano
mailto:tomokoy@xxxxxxxxx
http://www.charm.net/~tomokoy/
-All the photos (except panorama) with OM's-
http://ep.com/ep/csp.html?csp=1130
-Olympus Equipment Classifieds-

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