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08-23-2010, 01:40 PM   #1
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Meaning of ED, AL + IF in a lens ?

I've always as long as I can recall, been an enthusiastic photographer.

However technical aspects of photography escape me. I don't have a clue how all the diodes, sensors, specialized glass, etc...work. I'm just eternally grateful that they do work and allow me with minimum knowledge, to take pictures.

A few months ago I bought a Pentax 12-24 mm wide angle lens.

It's absolutely great.....clarity is something else...could be the best lens I have in my arsenal.

I note that the box it came in, tells me that it is a 12-24mm F4 with ED, AL and (IF).

I know what the 12-24mm means, I also have a grasp of the F4.....but what does the ED, AL and (IF) mean and how do they make this lens such an excellent photographic tool ?

08-23-2010, 01:49 PM   #2
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ED = Extra low dispersion glass to reduce color aberrations

IF = Internal focus system which means the lens doesn't get longer or shorter as it focuses. This can be important on large lenses because and external focusing lens can shift balance of the camera dramatically.

AL = Aspherical lenses which indicates it has at least one aspherical element in it to improve corner sharpness, especially in wide and ultra wideangle lenses.

Pentax Lens Terminology

Various manufacturers have similar and/or related terminology.
08-23-2010, 01:57 PM   #3
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QuoteOriginally posted by lesmore49 Quote

I know what the 12-24mm means, I also have a grasp of the F4.....but what does the ED, AL and (IF) mean and how do they make this lens such an excellent photographic tool ?
ED = Extra Low Disperstion
IF = Internal Focusing
AL = Aspherical Elements

Internal Focusing means your focusing mechanism is internal and does not extend or rotate your end element during focusing. It also allows a minimun focus distance (MFD) to be true/same across the focal range of a zoom lens. Example: DA* 16-50 Lens- At 16mm MFD is 10 inches at 50mm MFD is 10 inches.

Extra Low Dispersion Glass/Elements reduce chromatic aberration.

Aspherical Elements I'll let someone else do this one, but I believe its to keep corner to corner sharpness. (Blue nailed it)
08-23-2010, 02:09 PM   #4
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This is the diagram of the optical formula and layout of the A* 200mm/2.8 the blue elements are the ED ones in this lens.



Its predecessor, the K 200mm/2.5 didn't have the ED elements.




Some manufacturers use SLD (super low dispersion), ELD (extra low dispersion) and UL (ultra low) to refer to these elements . They may be made of lanthanum oxide, calcium flouride, zirconium dioxide or other materials depending on the era in which the lens was made including things like thorium dioxide. I believe the blue elements in the A* above are lanthanum.

08-23-2010, 03:14 PM   #5
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QuoteOriginally posted by Blue Quote
Some manufacturers use SLD (super low dispersion), ELD (extra low dispersion) and UL (ultra low) to refer to these elements . They may be made of lanthanum oxide, calcium flouride, zirconium dioxide or other materials depending on the era in which the lens was made including things like thorium dioxide. I believe the blue elements in the A* above are lanthanum.
Also the new Sigma/Hoya FLD glass, used to apparently positive effect in the former's 8-16mm and 17-50mm OS zooms. FLD standing for 'F Low Dispersion' (no, really :P)
08-23-2010, 04:55 PM   #6
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All Pentax terminology is explained here: Pentax K-Mount Lenses Explained: The differences between various Pentax lens series

Here on the forum, lots of acronyms are also auto-expanded (just over over them to see what they mean!). Examples:
SMC
SDM

Adam
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08-23-2010, 04:59 PM   #7
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Wow thats pretty awesome! Thanks Adam!
08-23-2010, 05:57 PM   #8
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Thanks to all. Very informative posts. Much appreciated.

Les

08-23-2010, 06:43 PM   #9
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Note, though, that the humble 18-55 also uses AL elements, and the equally humble 50-200 uses ED. So these aren't limited to unusually high end lenses.
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