L series technology

<p>So I just picked up the canon 17-40L f/4, and am really impressed with it. It is my first L series lens, and going from my tamron lenses its just unbelieveable as I'm sure anybody who has used one already knows. I was looking on Canon's website, and they talk about how they use manufactured flourite in their L-series line. They have a lot of literature on this flourite mainly because they say it has a low refractive index. My question is do they use this flourite in all of their L- series lenses, or are some of them outfitted with just the super UD glass?</p>

<p>Fluorite is generally used in telephoto lenses. Several of the 70-200 L lenses use fluorite, but as far as I know no shorter lenses do. All of the supertelephoto lenses have fluorite elements, usually large ones. The 17-40 does incorporate an ultralow dispersion element, which has benefits similar to fluorite.</p>

<p>The "L" Series is comprised of lenses containing one or more of these following optical features:<br>

*fluorite glass<br>

*ultra-low dispersion (UD) glass<br>

*aspherical element(s)<br>

*diffractive optical elements (DO)</p>

 

<p>Actually none of the Ls have diffraction optics... the DO lenses (there are only two, the 400/4 and 70-300 DO) are not L lenses, though they carry an L price tag.</p>

<p>And many lenses have aspherical elements or UD glass but are not L lenses...</p>

<p>Yeah I figured the shorter lenses didnt have the flourite in them. I know that flourite is supposedly more desirable for longer lenses. Regardless that 17-40 is still sharp as a tack, and of course my favoite lens. It was just a curious question anyways after spending that much on a lens. I appreciate the responses.</p>

<p>Canon publishes a book, Canon Lens Works, which is currently in edition III. It talks about their lenses and the technology behind them. There's a fair bit of we're-so-great fluff in it, but there's also quite a bit of useful information. You can buy it at a bookstore, or download it in PDF form at</p>

<p>http://www.canon-europe.com/Support/Documents/digital_slr_educational_tools/en/ef_lens_work_iii_en.asp</p>

<p>There's a section on fluorite and UD lenses on pages 200-202.</p>

<p>Nice catch there- yes, I forgot that they distinguish between Ls and DOs. How odd that Canon chose to adorn the latter with a green stripe, as their earliest fluorite lens was the FL-F 300 f/5.6 of 1969 and it too wore a green ring. In terms of technology and high performance I tend to think of it as being the "honorary" first member of an optical line eventually named "L" by an oh-so-clever marketing department!</p>

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<p>They have a lot of literature on this flourite mainly because they say it has a low refractive index.</p>

 

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<p>Mike, the important feature of fluorite is not just that it has low refractive index but that the relationship between refractive index and frequency (colour) follows a different curve from that of the various types of glass used in lens manufacture. This makes it possible to use fluorite in conjuction with several types of glass to produce lenses with very low chromatic aberration, thereby solving a problem that particularly affects long telephoto lenses. Canon were the first to develop a technology to grow the very large flawless fluorite crystals that are required to form part of the main converging element of such lenses. I have heard it said that the fluorite elements in the legendary 1200/5.6 took twelve months to grow, which gives you some idea of why such lenses are expensive.</p>

<p>Nowadays the L-series designation is a guarantee of a very well-built lens (that was not always the case), but some non-L-series lenses have optical performance comparable with that of L-series lenses, for example the EF-S 10~22, 60/2.8, and 17~55/2.8 the EF 85/1.8 (not quite as good as the 85/1.2L, but better than most L-series zooms), and the TS-E 45 and 90.</p>

<p>Enjoy usimng your 17~40. You'll come to think of the purchase of your first L lens as the first step into an expensive addiction!</p>

<p>It is interesting how Canon expanded the definition of the L series lens as the FD series progressed and it then moved to the EF mount. In the old FD days the you had the 14 F2.8, 24 F1.4, 50 F1.2L (the other 50 F1.2 was not L series), 85 F1.2300 F2.8, 300 F4400 F2.8, 500 F4.5800 F5.6 and five zooms (20-35 F3.5, 50-300 F4.5, 80-200 F4L and 150-600 F5.6). Lenses like the 135 F2, 200 F2.8, 35 F2.8 Tilt Shift were not classified as L series - nor was there an L series standard zoom.</p>

<p>I think there are lenses out there with many or some of the criteria of L lenses, that are otherwise excluded (EF-S, whatever). Originally it was the presence of certain types of 'glass', as already said.<br>

Green stripes are nearly as expensive to produce as red stripes, so don't lose your stripes, people. :P</p>

<p>Congratulations on your purchase, Mike. It's ironic that I came upon your post conveying the excitement you're feeling with your new 17-40 just as I'm contemplating selling mine. It is a very fine lens, but I also have a 35/1.4 L and 24/1.4 L II, and rarely shoot wider than 24mm.</p>

<p>I believe every L lens has at least one "special" element included in the optical formla. That said there is a video of (I believe) a 500mm L lens being made in the Canon factory. It explains about the complexity of making special glass elements and goes on to show the care in which L lenses are made. It might have had a link on this forum. Very interesting to view.</p>

<p>Congrats on your first "L" Mike. I think the 17-40 is a wonderful lens and it has been used a lot on all of my EOS cameras, film and digital, and with my 24-105L the two cover a nice focal length range. I'm about to purchase a couple of new Ls myself, the 100-400 and the 35/1.4L for use on my 7D with the 35L giving me the nearest 35mm-equivalent of a 50/1.4 on the 7D. Don't forget though that there are a number of non-L lenses that are outstanding performers as Robin pointed out. I will add the 15-85mm EF-S lens to his list as another outstanding lens that is incredibly sharp, has a great build quality, and has the ultra-low dispersion and aspherical elements in it. It really is a wonderful lens that covers a 35mm-equivalent focal range of 24-136mm on my 7D. Enjoy the 17-40 though, as it's a first class optic and a lot of fun to use.</p>

<p>Yeah speaking of non L lenses that are sharp. I have that 100mm macro from Canon. Picked it up used in mint condition for $390. Some of the pictures I have taken with that lens just blow my mind, and I can't believe the detail. I went from a Tamron 28-70 2.8, and when I got the 17-40 I did a random focus test. Set the camera on a tripod, and tried to focus with both on something that was about a foot away. Before I did I took the focus ring, and set it to infinity so the lenses would have to go through their entire range pretty much. The tamron was slow, and inconsistent since there were times where it would not focus at all. The in focus light in the viewfinder would flash telling me there wasn't enough light. The 17-40 was instant, always worked, and super quiet. What have I learned from all this? Canon lenses L series, and non L series are best for canon bodies. Same for the Nikon lenses on the nikon bodies. </p>

<p>This is very timely - I just shot with my 24-105L last night as well as my 50 1.8 Mk 1. Same lighting, same ISO. Of course the 24-105 has IS but I was shooting fast enough that it really didn't come into play. Nevertheless the difference between the L and non-L is amazing in terms of sharpness, color and contrast. Stunning quality.</p>

<p>My 85/1.8 and 50/1.8(I) are MUCH better then 24-105L zoom in terms of everything except IS.</p>

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<p>My 85/1.8 and 50/1.8(I) are MUCH better then 24-105L zoom in terms of everything except IS.</p>

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<p>Interesting. Don't get me wrong Igor - I like my 50 1.8 (I) very much, it's an excellent lens. But out of the box, the 24-105 far exceeds it's performance at similar aperture settings.</p>

<p>I find the 50 1.8 is best above f2.8. At 1.8 it vignettes like crazy.</p>

<p><em>My 85/1.8 ...[is] MUCH better then 24-105L zoom in terms of everything except IS.</em></p>

<p>Theoretically I totally agree. No way the 24-105 at 85mm has anything on the 85 1.8.<br>

I'll test this for real soon as my neighbor just bought a 24-105.<br>

The 85mm is probably sharper, far fewer optical flaws, and focuses faster than the 4L does.<br>

We'll see... I've not seen them compared head-to-head yet.</p>

<cite>*aspherical element(s)</cite>

 

<p>Just to expand slightly on what others have said about this, Canon has several different methods for producing aspherical elements, including a special grinding process that directly produces aspherical elements, glass molding, and applying an optical resin to a spherical element to produce an aspherical element. Of these, I think only grinding counts toward qualifying a lens as an L (though other types are also present in some L lenses).</p>

 

<cite>How odd that Canon chose to adorn the latter with a green stripe, as their earliest fluorite lens was the FL-F 300 f/5.6 of 1969 and it too wore a green ring.</cite>

 

<p>At one point during the fairly long gestation of the 400/4 DO, Canon <em>did</em> refer to it in a press release as an L lens. Whether this was a typo or a reflection of an internal debate about whether or not it would qualify (it offers L levels of optical performance, build quality, weather sealing, and price, and includes a fluorite element), I have no idea.</p>

 

<cite>I think there are lenses out there with many or some of the criteria of L lenses, that are otherwise excluded (EF-S, whatever).</cite>

 

<p>There are indeed EF-S lenses which have L-type elements in them, and certainly both the 10-22 and the 17-55 are widely regarded as offering image quality comparable to L zooms, but presumably any lens that can't be mounted on a pro body automatically disqualifies itself from being an L lens. In recent years, L-type elements have also started appearing in some lenses that <em>can</em> be mounted on pro bodies (e.g. the non-DO 70-300 IS, which has a UD lens) but that aren't L lenses and therefore don't have L build quality.</p>

 

<p>Professional build quality wasn't really a requirement for an L lens in the earlier years of EF lenses (for instance, the L and non-L 100-300 f/5.6 twins were, well, pretty much twins other than the optics), but since perhaps the mid-1990s, it seems to be, and since the advent of specific dust- and water-resistant features in lenses in the late 1990s, that too has become an expected feature of an L lens. Meanwhile, the L family has also been expanded from its original market (squarely aimed at pros) to include higher-end consumers. The constant f/4L zooms are certainly usable by pros and are up to pro standards in every way, but really, they're aimed at consumers who want pro-quality optics and build quality but want an option with a price tag that falls between consumer zooms and the full-on pro f/2.8 zooms. So what is or is not an L lens has changed over the years.</p>

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<p>And many lenses have aspherical elements or UD glass but are not L lenses...</p>

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<p>Alan, that's totally wrong. L lenses do, in fact, utilize UD(ultra low dispersion)glass.</p>

<p>Brian, I did not say no L lenses use UD glass. I said some non-L lenses use UD glass.</p>

<p>L lenses by definition do include either UD glass elements or Fluorite. There is no such thing as "some non-L lenses" using UD.</p>

<p>Another thing is that the 400mm f/4 DO is "considered" by some not to be an L lens but it actually is. It has the famous white or putty color, as well as containing fluorite.</p>

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<p>There is no such thing as "some non-L lenses" using UD.</p>

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<p>Don't argue with me, argue with Canon.</p>

<p>http://www.canon.com/camera-museum/camera/lens/ef/data/ef-s/ef_s55~250_4-5.6_is.html</p>

 

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<p>The “EF-S55-250mm F4-5.6 IS” is a telephoto zoom lens.... The inclusion of a UD (ultra-low dispersion glass) element in the design provides excellent aberration correction...</p>

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<p>I'm not arguing with you, just trying to educate you.</p>