How does the ED lens affect the image?


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sgfriend

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Learn that the DX 18-55 (kit lens from D50) has 1 ED len and DX 18-70 (kit lens from D70s) has 3 ED lens. Any different? Their f/stop is the same right? :dunno:
 

mpenza

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it's to improve image quality (contrast, sharpness and reduce the splitting of colours as they pass through the elements)... the number of such elements required depends on the lens design and there're differences in the "ED" coating. A better "ED" element could be more effective than a few normal "ED" elements.
 

sgfriend

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Does that mean... the more ED lens the better and it's more expensive?
 

Astin

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IIRC, diff light colour travel at diff speed, so they wont focus at exactly the same point, the ED lens element is meant to compensate for the diff, so all colours will focus at the same point.
 

Artosoft

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Astin said:
IIRC, diff light colour travel at diff speed, so they wont focus at exactly the same point, the ED lens element is meant to compensate for the diff, so all colours will focus at the same point.
To prevent or lower chromatic aberration (colored fringes).....

Regards,
Arto.
 

espn

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Astin said:
IIRC, diff light colour travel at diff speed, so they wont focus at exactly the same point, the ED lens element is meant to compensate for the diff, so all colours will focus at the same point.
Bingo, Extra-low Dispersion ;)
 

espn

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Astin said:
IIRC, the ED element is actually plastic, not really glass, I still prefer glass...
IIRC, the ED element is glass leh :what:
 

johnyu

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Astin said:
IIRC, the ED element is actually plastic, not really glass, I still prefer glass...
I think you mixed up.

ED elements are glass.

But aspherical elements used in budget lenses are moulded (aka "plastic"). I think Tamron pioneers this technology. (But not all aspherical elements are plastic.)
 

Astin

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johnyu said:
I think you mixed up.

ED elements are glass.

But aspherical elements used in budget lenses are moulded (aka "plastic"). I think Tamron pioneers this technology. (But not all aspherical elements are plastic.)
Maybe u are right, I only remember very vaguely reading from some Nikon articles that they cannot bend the glass so easily so they use plastic instead, forgotten whether they refer to ED element or aspherical element, something about physics of glass / air properties.
 

Ian

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Astin said:
IIRC, diff light colour travel at diff speed, so they wont focus at exactly the same point, the ED lens element is meant to compensate for the diff, so all colours will focus at the same point.
Light regardless of colour travels at exactly the same speed actually. What varies is the length of the wave that is propogated or in otherwords it's frequency.
Astin said:
Maybe u are right, I only remember very vaguely reading from some Nikon articles that they cannot bend the glass so easily so they use plastic instead, forgotten whether they refer to ED element or aspherical element, something about physics of glass / air properties.
Nikon don't bend lenses. Tey are rough cast to shape, then ground and polished using a variety of technologies depending on the lens element being produced. Aspherical elements used in Nikkor lenses are made from both glass and optical plastic and it depends on the lens (and element) as to the material being used.

ew words about ED and Apsherical lens elements
ED lens elements are merely lens elements made from a glass of special composition that refracts all the wavelengths of visible light to a common focus point. ED elements help reduce bifringent and chromatic abberations in general. The coatings used along with the glass used also assists in increasing the contrast ratio of the image which results in shots with more colour vibrancy and accuracy. ED glass was first used by Nikon in 1970~1 in it's 300mm telephoto lenses from memory.

Aspherical lens elements have been around for years and years. I seem to recall Tamron was the first lens manufacturer to use plastic aspherical elemements in ther lenses as early as the mid 1980s. Again if memory serves me right (correct me if I'm wrong) Nikon first used an aspherical lens element in their old 21mm f3.5 lens from about 1959~60.
 

Astin

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Ah, no wonder I didnt score A in my physics, I mixed up speed and frequency, also mixed up bending and casting...:sweat:

It happens to everyone Astin. precasting or spinning a lens to a rough shape is a recent development, and is used along with CNC machining to rough shape the lens. Some are still shaped from flat glass the hard way though, it all depends on the curvature of the element and the size of the production run. Camera lenses aren't actually that accurate anyway, not compared to precision optics used in other fields.
 

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