Thanks for the piece on lateral color. I hadn't thought about checking
the magnification of the various color channels.
Chuck Norcutt
Carlos J. Santisteban wrote:
> 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,
--
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