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Old Aug 23, 2010, 2:57 PM   #1
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Default What does ED, AL and (IF) mean 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 ?
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Old Aug 23, 2010, 4:21 PM   #2
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ED = extra-low dispersion glass elements, reducing chromatic abberation. Not reducing the price of the lens, unfortunately.

AL = aspherical elements, used in wide angle lenses to get a flatter focus field and better corner/edge sharpness. Like ED, it costs more.

IF = internal focusing. Only glass elements inside the lens moves when you focus, the rear and front elements keep in place. The lens keeps the same size at all focusing distances. A bit more complicated for the engineers, thus adds to the price of the lens.

So now you know why the 12-24 isn't given away for free!

For more detailed information and other abbreviations see http://www.bdimitrov.de/kmp/technology/lens_terms.html


Kjell
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Old Aug 23, 2010, 7:55 PM   #3
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Thank you Kjell for the detailed info and the link. Much appreciated.

Les
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Old Aug 23, 2010, 11:36 PM   #4
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Hi Les,

I thought I'd add a few comments to Kjell's very good explanations if you're interested.

ED is Pentax's term, but it is essentially equivalent to APO (apochromatic) for Sigma and LD (Low Dispersion) for Tamron, and SD (Super low Dispersion) or HLD (High refractive Low dispersion) for Tokina. In my experience, ED and APO elements are pretty equivalent for CA reduction, and LD and SD are pretty close, but ED and APO seem to outperform the equivalents from Tamron and Tokina. I've not used an HLD equipped lens from Tokina, so I don't know how effective these elements are.

AL (Pentax) = ASP (Sigma) = Aspherical (Tamron) = Asp (Tokina). Aspheric lens elements can also make the front element smaller, making for a significant reduction in overall size for the lens. Front element size is usually dictated by FL and max aperture, but aspherical lens design (the shape of the lens curvature is not simply a section of a sphere like the great majority of elements) can also be used to change this relationship. The complicated grinding process makes these elements more expensive to mfg, AFAIK

The most striking example I have is the Tamron 28-75 f2.8 XR Di LD Aspherical (IF) which has a 67mm front element (in addition to the longest name in the history of lenses) compared to the Sigma EX 24-70 f2.8 DG Macro at 82mm, and the Tokina 28-70 f2.8 AT-X Pro which had a 77mm front element.

(IF) also adds a bit to the length of the lens, and tends to be a bit faster in AF systems since the internal focusing elements tend to be smaller and lighter than an inner lens barrel moving the front element. Rear Focus (RF) designs in long tele lenses also aid in focusing speed for the same reason.

I've found these seemingly "too techie" details actually played into my decisions to buy a particular lens over an alternative, so I thought them worth mentioning.

Scott
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Old Aug 24, 2010, 11:16 AM   #5
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Quote:
Originally Posted by snostorm View Post
Hi Les,

I thought I'd add a few comments to Kjell's very good explanations if you're interested.

ED is Pentax's term, but it is essentially equivalent to APO (apochromatic) for Sigma and LD (Low Dispersion) for Tamron, and SD (Super low Dispersion) or HLD (High refractive Low dispersion) for Tokina. In my experience, ED and APO elements are pretty equivalent for CA reduction, and LD and SD are pretty close, but ED and APO seem to outperform the equivalents from Tamron and Tokina. I've not used an HLD equipped lens from Tokina, so I don't know how effective these elements are.

AL (Pentax) = ASP (Sigma) = Aspherical (Tamron) = Asp (Tokina). Aspheric lens elements can also make the front element smaller, making for a significant reduction in overall size for the lens. Front element size is usually dictated by FL and max aperture, but aspherical lens design (the shape of the lens curvature is not simply a section of a sphere like the great majority of elements) can also be used to change this relationship. The complicated grinding process makes these elements more expensive to mfg, AFAIK

The most striking example I have is the Tamron 28-75 f2.8 XR Di LD Aspherical (IF) which has a 67mm front element (in addition to the longest name in the history of lenses) compared to the Sigma EX 24-70 f2.8 DG Macro at 82mm, and the Tokina 28-70 f2.8 AT-X Pro which had a 77mm front element.

(IF) also adds a bit to the length of the lens, and tends to be a bit faster in AF systems since the internal focusing elements tend to be smaller and lighter than an inner lens barrel moving the front element. Rear Focus (RF) designs in long tele lenses also aid in focusing speed for the same reason.

I've found these seemingly "too techie" details actually played into my decisions to buy a particular lens over an alternative, so I thought them worth mentioning.

Scott

Thanks Scott.

I find that my 12-24 mm is quite a marvelous lens. I take a lot of pix of vintage cars. Up to May 2010, I would usually use my 16-45 lens for this duty, but as mentioned as of May, when I bought the 12-24mm, the 12-24mm is almost used exclusively for vintage car shots.

I was mentioning to my wife the other day that while occasionally I would get a really sharp pix from my 16-45mm...that with the 12-24 mm the percentage of really sharp pix that seem to leap out in the photo, has become a regular occurrence.

I'm not bragging about my photo skills, as I believe it has all to do with the 12-24mm attached to my K10D.

The 12-24mm seems to produce auto pix (dependent on outside lighting that seem out of a brochure. I'm not using RAW, I'm using the top JPEG.

The 12-24 is very expensive in Canada and I admit I had to take a deep breath before I bought it, wondering if it was worth it's price. As it happened I got a very good deal.

The lens with all it's specialized glass is a premium performer, worth the price, IMO.

After your and Kjell's detailed explanations of what makes this lens work so well, I can understand the price.

Thanks Scott.


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Old Aug 26, 2010, 1:55 PM   #6
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Quote:
Originally Posted by snostorm View Post
The most striking example I have is the Tamron 28-75 f2.8 XR Di LD Aspherical (IF) which has a 67mm front element (in addition to the longest name in the history of lenses)
Let's see:

Tamron 28-75 f2.8 XR Di LD Aspherical (IF) = 42 characters (with spaces)

Schneider-Kreuznach Betavaron 3,5...11/0.08 Kreonite = 52 characters
(leave off the Kreonite [distributer's name] and it's still 43 characters)

Gundlach Turner-Reich Anast. F:7.0 12" 304.8 mm = 47 characters

This suggests another worthy thread:

What is your lens with the longest name, excluding serial numbers, and without expansion of abbreviations?
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