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[OM] CA

Subject: [OM] CA
From: usher99@xxxxxxx
Date: Wed, 21 Oct 2009 15:55:08 -0400
Thanks for commenting ,Carlos.
The CV 125/2.5 Apo Lanthar must have a fairy restricted secondary 
spectrum.  I have seen 1:1 shots of type (not my favorite macro target)
showing less CA with the Viv S1 90mm with the matched TC but the CV is 
easier to use with smoother bokeh, if that is desired for the shot.
No TC required and the VF is brighter at higher mag.  I wouldn't sell 
Big Foot for twice what I paid.   I guess it is not "superachromatic" 
though.
Mike





Hi Mike and all,

From: usher99@xxxxxxx
>Kinda liked the below explanation of terms.  The CV 125/2.5 Apo-Lanthar
>shows some CA in in the foreground OOF area if there is a sharp edge of
>contrast at 1:1 esp if on the Mirex T-S adapter. Perhaps this is a 
special
>OOF CA.

Most likely longitudinal CA -- unlike lateral colour, basically 
impossible
to correct via software :-(

>APO  clearly does not = NO CA under all conditions.

Absolutely -- just a better degree of correction.

<http://toothwalker.org/optics/chromatic.html>

A very interesting site... it however lacks an explanation of
spherochromatism -- the variation of spherical aberration against
wavelength.

Anyway, I wouldn't test CA on heavily overexposed areas -- either on 
film or
digital. CA has real existence, but in _some_ cases could be just 
lateral
halation/bleeding or other film/sensor issues.

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


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