Holla David,
I've visited your test pages and in fact the images show horrible
coloured fringes.
David Irisarri Vila wrote:
> My gallery is based in PhotoCD,
But you are aware that Kodak's Photo CD scanners haven't the highest
resolution and suffer from an serious blooming problem? Check at Tony
Sleeps scanner test page.
There are some test images showing exactly the same coloured fringes,
introduced by scanner. Even some of the more expensive models, as the
Nikon Coolscan LS2000 suffer from it.
> I also use my UMAX Powerlook
Results from a second generation image are less reliable because there
are to many variables which might have introduced the error.
> I use my scanner
> with photographs (PORTRA paper) and Ektachrome slides to
> scan images for the web.
If your slides show that horrible colour fringes on images created by
an flatbed scanner it's either the scanner or your lens is serious
damaged. But then, you should be able to see the error with bare eyes
on the slides.
"and you can see this chromatic aberration even into photographic
paper at 10x15cm!!!"
10x15! No way! At that tiny size nobody would be able to see the flaws
of my 180mm lens.
"I've also projected it with my NORIS projector. Chromatic aberration
is terribly high!!!"
Projecting lenses are designed for specific enlargement ratios,
Projections beyond that borders will quick show the limitations of the
_projecting_lens_, including colourful fringes.
I don't want to trash your projector, but cheaper projecting lenses
might introduce serious flaws even in moderate enlargements.
After the first reports of chromatic aberrations produced by the 180mm
lens, some time ago, I made an home made test to check my lens.
I mounted a piece of black cardboard onto a white window frame and
photographed it from the inside at an distance of approximately 3m.
Took several photos at different apertures and with different EVs.
Pretty extreme conditions, but I was not able to reproduce that
coloured fringes someone has described.
I've no longer the test slides, but last week I took some photos with
the 180mm at the World Expo. After reading your initial mail I
carefully examined my slides for chromatic aberration with no result.
C.H.Ling wrote:
"It sure has some, most visible in the high light area. If your shot
does not contain bright spot there will be no problem."
The slides contain fine detail against the sky, white writing and
black lines on red background, black structures against the blue sky,
metallic reflection of the buildings wall cover.
I'm sorry but I've no scanner yet, but I'm considering to buy one.
I checked it with loupes* with no result but to show the limits of the
loupes by introducing coloured fringes. One knows it's introduced by
the loupe because the colour changes while moving the loupe.
Next stage projecting the slides. I've an Kodak S-AV 2050 projector,
for a long time the standard in Europe for professional projecting.
The projector is equipped with Kodak Retinar S-AV 2000 60mm PC and
90mm PC lenses**.
I couldn't see coloured fringes in the images with the 90mm lens at
aprox. 30x enlargement. At aprox. 45x enlargement with the 60mm
lens... oh s##t, some coloured fringes are visible when looking very
close at the screen! Hmm, crosschecking with an b/w slide. Again
coloured fringes, on a b/w slide! So it must be the projecting lens.
End of test, the limiting factor seems not to be the 180mm lens.
So if someone asks why do you use that crapy US$350 lens (new price in
1992), I'll answer: Because it's an excellent projecting lens used
within the specs it was designed for, there is no superior
alternative.
Under that viewing condition, I was able to see chromatic aberration,
I would have other problems than coloured fringes, seeing the whole
picture would have been impossible at that distance.
I had an 50mm projecting lens because I like the big picture. I sold
it because regardless how hard I tried I was not able to have an sharp
projection, corner to corner. Limiting factor was not the lens but the
slide not lying flat in the projector. I tried hard, tested all
available slide mounts, no avail.
Only solution was looking at the picture from a bigger distance or
using a lower enlargement, longer focal length.
My conclusion is 60mm is the shortest focal length one can use for
standard projection conditions. Those shorter lenses are made for rear
projection and moderate enlargement.
C.H.Ling wrote:
"Stop down the the lens does not seems to improve the situation."
Conventional wisdom would indicates that the colour error of lenses is
less noticeable with smaller apertures (only to grow again if an
optimum aperture has passed).
Did you check that nowhere else in the chain of reproduction has been
made an error?
I don't care about the performance of my lenses as long as they are
not the limiting factor.
Anyway it's not possible to cheat the laws of nature. Newton stated,
it's not possible to eliminate the wavelength (colour) depending
focusing error. One can only try to reduce it to an usable amount. If
one tries hard enough, one might reveil the chromatic error of every
lens.
Best regards
Richard
*an cheap 10x loupe and an 50mm Zuiko.
**No that aren't el cheapo plastic lenses, both are PC (perspective
corrections, shift) lenses with full metal lens barrel and multicoated
lens elements. Those lenses are AFAIK not made by Kodak but either by
Schneider or more probably by Docter Optic, both have identically
looking lenses with identical specifications for offer (save the
writing on the lens barrel). Docter Optic is now owned by Leica and
"surprise" two similar looking lenses are now available for Leica
projectors under the name PC Elmarit-P 60mm/2.8 and 90mm/2.8.
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