Let´s see C.H.Ling,
Everybody should visit this site, because it explains very
well chromatic aberration and suggests how to solve this
problem.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/aber2.html
A lens will not focus different colors in exactly the same place
because the focal length depends on refraction and the index of
refraction for blue light (short wavelengths) is larger than that
of red light (long wavelengths).
-------------------------------------------------------------------
The amount of chromatic aberration depends on the dispersion of
the glass.
-------------------------------------------------------------------
So, The longer the focal length, the more visible chromatic
aberration is. ED ("extra-low dispersion") glass has lower
dispersion, so it reduces the amount of chromatic aberration.
This is necessary to get high magnifcations without color fringing.
Dave
"C.H.Ling" wrote:
>
> Hi David,
>
> Here I don't agree with you, my 200/4 and 85-250 didn't found this problem,
> they didn't possess any ED glass. With good design the problem can be
> eliminated even without ED glass, but there may be some trade off, on the
> other aspect the 180/2.8 is unbeatable. At the mean time I think not all ED
> glasses are made with fluorite, which seems mention a lot only in Canon's
> old fluorite lenses.
>
> The Camedia's problem may not due to the lens, the same problem happen also
> with Nikon's 950. Most likely it was the problem of the CCD and its color
> calculation/manipulation method.
>
> C.H.Ling
>
> -----Original Message-----
> From: David Irisarri Vila <valicors@xxxxxxxxxx>
> To: olympus@xxxxxxxxxxxxxxx <olympus@xxxxxxxxxxxxxxx>
> Date: Sunday, September 03, 2000 7:59 AM
> Subject: Re: [OM] Zuiko 180 TEST !!!
>
> >Hi C.H.Ling,
> > Your pictures are perfect for showing this type
> >of chromatic aberration. This is normal because this
> >isn´t a fluorite special glass and you cannot solve this
> >problem with coatting or making groups of elements.
> >I think that everybody has this problem, and Olympus gave
> >us a terribly heavy solution. Zuiko 180/2
> > Of course that other Zuiko lenses should have this
> >problems, even my CAMEDIA that takes a very high quality
> >zoom lens has this problem, due to the lack of ED glass.
> >Olympus with the new 35-140 f2-2,4 will be again in the
> >first line!!!
> > Finally I´m with you that you won´t reduce chromatic
> >aberration, stopping down. Never!!!
> >
> >Dave
> >
>
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