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Re: [OM] picture link

Subject: Re: [OM] picture link
From: "Carlos J. Santisteban" <zuiko21@xxxxxxxxx>
Date: Fri, 3 Jul 2009 13:41:02 +0200
Hi Chuck, C.H and all,

>> C.H.Ling wrote:
>>> Hi John,
>>>
>>> I think this is the picture you wanted:
>>>
>>>
http://a.img-dpreview.com/gallery/olympusep1_preview2/originals/p6160172.jpg


Chuck wrote:

> I meant to add that the color fringes seem to have distinct horizontal
> and vertical components.  AFAIK, CA is something which gets worse the
> farther away from the optical axis.


That is the case of the transverse CA, a.k.a. "lateral colour". However,
unlike axial CA, it won't improve by stopping down :-(


> So it should be radially
> distributed and not horizontally and vertically.  However, pixels are
> horizontally and vertically distributed so I think this fringing is
> somehow related to the sensor and/or processing as AG suggested.


I have looked at the different colour channels in PS... and the red channel
shows a _bigger_ image (higher magnification). There's also a slight
difference in scale between the green and blue channels, but too small to be
an issue.

Should the red channel were shifted only, I could think of a
sensor/processing issue... but with the difference in size (unless
voluntarily caused by a _very_ wicked/twisted processing firmware :-) it
only can be transverse CA, lateral colour -- and would remain the same at
f/2.8, f/6.3 or f/22 :-(

C.H. Ling wrote:
>What about this one at F2.8?
>
>http://pliki.optyczne.pl/ep1/17/foto04.jpg

The centre is very well defined, but it's no surpirse. The corners of this
picture have no detail to disturb by transverse CA... in fact, the sign at
the right side is white on red, which is inmune to this kind of CA. However,
some lateral colour can be seen at the top (white on sky) and at the
sculpture at the left.

Shooting at f/2.8 doesn't impair things wiht _transverse_ CA.

Cheers,
-- 
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
-- 
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