Why is wide *and* fast so hard to do?

[tim_klimowicz]

<p>It seems that 50mm is the sweet spot for a 1.4 or faster lens, and than any lower (24mm) or higher (85mm) results in a much more expensive lens.</p>

<p>I understand that longer lenses are harder (more expensive) to make fast because it demands an enormous amount of glass to match the length, but why does the opposite not seem to hold true for wider lenses?</p>

<p>I ask this because I guess I'm just trying to understand why 24mm seems to be the cut-off point for very fast wide lenses. Any wider and the aperture starts to creep up to the 2.8 (16-35mm) or even worse (10-22mm 3.5-4.5).</p>

<p>And I'm trying to understand this only because I wish there was an option even remotely close to the 24mm 1.4 on an APS-C body. There's options that are much wider, but at a pretty big loss of aperture. Is there just no market for something that fast and wide, or is there some sort of physical barrier which prohibits making such lenses with decent quality?</p>

[scott_ferris]

<p>Aberrations, wides are much, more difficult to deal with the distortions intrinsic to the wide angles. Speed adds to the complexity. Retro-focus designs, the lens is longer than the focal length so you are projecting the image back to the focal plane. Wides are much more complicated than teles, they have to bend the light and that creates its own problems.</p>

[PuppyDigs]

<p>Yes, there is a physical barrier which prohibits making such lenses and that barrier is friggen greenbacks. I'm sure Canon could make a fast ultra wide but only a few well-heeled folk would have the wherewithal to buy it. Have you seen the EF 35 1.4L? It's a real monster compared to the 50 1.4. Its easy and inexpensive to make a good 35 2.0 but a wee bit larger aperture means more elements for correction, better coatings for all those elements, erotic glass for better transmission and aspherical elements to chase away distortions. And it gets harder the wider you go.</p>

[alan_bryant1]

<blockquote>

<p>erotic glass</p>

</blockquote>

<p>Puppy, I think you're over-interpreting the whole phallic symbol thing.</p>

[PuppyDigs]

<p>Short 'n wide I suppose is optica erotica to some. It helps to wear a hood.</p>

[digitmstr]

<p>for 'better transmission'...no less...</p>

[joe_c5]

<p>As I understand it, one of the main reasons is that wide angle lenses on SLR cameras need to use retrofocus designs (basically inverted telephoto lenses) because the mirror would hit a symmetric lens at the shorter focal length.</p>

<p>Wider lenses are therefore more difficult to make fast for almost exactly the same reason as longer lenses.</p>

[tom_burke3]

<p>Leica last year announced and released 21mm and 24mm f1.4 lenses for the M system, but they're phenomenally expensive - almost twice the cost of the f2.8 lenses in those focal lengths. And the f2.8 lenses would generally have been regarded as 'ruinously expensive' before the new lenses came along.</p>

<p>So it's not just fast, wide lenses for SLRs that are expensive - fast, wide lenses for rangefinders are as well.</p>

[kelly_flanigan1]

<p>It is basic optics.<br>

It is also basic running/track too.<br>

Folks who are WIDE are typically not FAST!</p>

[Robin Smith]

<p>It is a basic rule I think that it is harder and more expensive to make a good wide angle than a good telephoto.</p>

[JDMvW]

<p>Among all the factors already mentioned, just think of the incredibly wide range of angles that the light rays are coming into the lens from. Then conceive of how difficult it is to correct those highly divergent rays so they all focus <em>together</em> on the film/sensor plane. It's just easier to correct a narrower angle of view. Only modern, high-speed computers make the computations even feasible.</p><div></div>

[tim_klimowicz]

<p>Thanks for the replies, everyone. Good info, and makes perfect sense.</p>

[kelly_flanigan1]

<p>This dinky lens design goes back even before WW2; when a computer was persons job title!<br>

<img src="http://i4.photobucket.com/albums/y148/ektar/METROGON/P3250063crop.jpg" alt="" /></p>