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Old Jun 7, 2002, 1:22 AM   #1
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Default What is CHROMATIC ABERRATION?

I own a 2 megapixel dig cam. I'm really limited when just relying on the internal 3x optical zoom.... so I have been researching the web and found the Kenko 3x teleconverter. I'm not looking for PROFESSIONAL results with this lens (to the point of having my picture framed on my wall).... I just want to know if this lens can provide decent pictures.

Anyway, most reviews on this 3x lens warn about chromatic aberration (like its some kind of chronic disease).

Please describe what this is in NEWBIE terms? Can it be fixed thru my Adobe PhotoDeluxe imaging software?

If it can't be fixed, is it something I can live with?


If anyone has SAMPLE pictures of what this is, please hyper-link them.
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Old Jun 7, 2002, 2:24 AM   #2
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Chromatic Aberration - Also known as the "purple fringe effect." It is common in two megapixel and higher resolution digital cameras when a dark area is surrounded by a highlight. Along the edge between dark and light you will see a line or two of purple or violet colored pixels that shouldn't be there.

This is out of our Digicam Dictionary

-Steve
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Old Jun 7, 2002, 10:51 AM   #3
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To be a little more specific chromatic aberration is a consequence of using refractive lenses. I'll assume you already know how a lens works, with the refreactive indexes and interfaces and the light getting all bendy. Problem is the refraction of light varies with wavelength, AKA color. If you use a simple, single element, lens and focus the red light the blue light can't also be in focus. Designers add additional elements to bring both red and blue into focus at the same plane. That's better but not completely corrected. More sophisticated lenses that bring three wavelengths (colors) into focus all together are called apochromatic and are found on better cameras. The only lenses that avoids chromatic aberration are pure mirror lenses. Pinhole cameras avoid it but have diffraction to deal with not to mention being poor for low light action.

I'm not suprised that the teleconverter has a lot of chromatic aberation. A fullly corrected add-on teleconverter would likely be tooh eavy and bulky to be practical not to mention much more expensive. Unfortunately I can't think of any solution for you that's both good and cheap.

For an example of chromatic aberration look at a white object through cheap binoculars with the object near the edges of the field of view. You'll likely see red and blue fringing around the edges



[Edited on 6-7-2002 by padeye]
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Old Jun 7, 2002, 11:29 AM   #4
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Default If you wear glasses...

that have a high-refractive index plastic lens you will know, intimately, what chromatic aberration is. Especially, if you have a large (wide & thick) lens. Scanning left and right yields yellow or blue fringing on nearly everything you look at.

It was pretty horrible with the plastics in use 15 years ago; somewhat improved today. Solutions: Smaller lens, closer to eyes; glass; contacts; surgery. Yeah, I'm a step or two short of coke bottle lenses.

Anyway, this can give you an idea of the "what" if you seek an example.
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Old Jun 7, 2002, 1:38 PM   #5
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Default CAs

For what it's worth and if you find this lens too low in quality have alook at the 5x eagle eye at www.eagleeyeuk.com.

Some of these cheap lenses are quite simply a waste of money. The eagle eye is high quality. You get what you pay for with optics.

Steve
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Old Jun 7, 2002, 8:16 PM   #6
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Default On Chromatic Aberration - CA

Quote:
I own a 2 megapixel dig cam. I'm really limited when just relying on the internal 3x optical zoom.... so I have been researching the web and found the Kenko 3x teleconverter. I'm not looking for PROFESSIONAL results with this lens (to the point of having my picture framed on my wall).... I just want to know if this lens can provide decent pictures.
It would help with making a recommendation if you could tell us what type of 2.1 (make and model) 3x camera you have. Some are much more amenable to tele converters than others.

If you have heard lots of complaints about chromatic aberration and the 3x Kenko in question, my suggestion would be to go for something else. About the only truly "safe" recommendation for a tele converter without knowing the specifics about your camera would be something like the Olympus B-300 1.7x. Even with the "best" teleconverters, you will sometimes get a bit of chromatic aberration. To a great degree, if it's not really bad CA, you can use one or more tools to remove it or at least make it less noticable.

Tell us more about the camera and there's a good chance a recommendation for the best match in a teleconverter can be made. There are many here on this forum who a very familiar with the entire range of tele converters and cameras...

Best regards,

Lin
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Old Sep 26, 2002, 6:25 AM   #7
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More than 200 years ago, Newton showed that white light was composed of multiple wavelengths. Simple lenses will refract (bend) light differentially as a function of wavelength. Short (blue appearing) wavelengths are refracted more than long (red appearing) wavelengths. Consequently, lenses like the one shown below will not image light all in one place.



A lens called an achromatic lens solves this problem

[Edited on 26-9-2002 by ajitkataria]
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