Superfast Glass

Fast lenses let you shoot in dimmer light and can really limit depth of field for selective-focus shots. Superfast lenses are even better, right? We’ll go into that in a moment, but first, what is a fast lens?

Fast refers to the size of the lens’ maximum aperture, and it’s a relative term in more ways than one. The ƒ-number designates the diameter of the lens’ maximum aperture opening relative to the lens’ focal length (i.e., ƒ/2 means the aperture diameter is one-half the focal length; ƒ/4 means it’s one-quarter the focal length), and fast depends on the focal length, as well. Sigma’s 200-500mm ƒ/2.8 APO EX DG zoom is the fastest 500mm lens available (and comes with a dedicated 2X teleconverter that makes it a 400-1000mm ƒ/5.6, the fastest 1000mm lens available). But ƒ/2.8 isn’t at all fast for a 50mm lens; ƒ/1.4 would be fast for a 50mm, and there are even faster ones. For this article, we’re considering the collection of elite lenses that are faster than ƒ/1.4, regardless of focal length.

Today, there are a number of lenses faster than ƒ/1.4. In fact, several are faster than ƒ/1.0—their effective aperture diameter is wider than the lens’ focal length. Note that a lens’ focal length and its physical length aren’t the same thing. The focal length is the distance between the optical center of the lens and the image plane when the lens is focused at infinity. For telephoto lenses, the optical center is actually in front of the front lens element. The physical length is, of course, the length of the lens from filter threads to mount. Wide-angle lenses are generally physically longer than their focal lengths, while telephotos, by definition, are shorter physically than their focal lengths.

Clockwise from top left: Canon EF 50mm ƒ/1.2L USM; Voigtländer 25mm ƒ/0.95 Nokton; Fujinon XF 56mm ƒ/1.2 R. BELOW: Leica Noctilux-M 50mm ƒ/0.95 ASPH

High-Speed Considerations

Fast lenses offer several advantages. For one, they let you shoot in dimmer light than slower ones because they let in more light. More light transmittance means you can use a faster shutter speed at a given ISO setting, or a lower ISO setting at a given shutter speed, in the same conditions. Combine the high-ISO capabilities of today’s DSLRs and mirrorless cameras, in-lens or sensor-shift image stabilization, and a fast lens, and you can shoot handheld in amazingly dim conditions.

Faster lenses provide brighter viewfinder images for composing and manual focusing with DSLRs, assuming your DSLR’s viewfinder can handle the lens speed (some DSLR viewfinders don’t actually appear brighter with lenses brighter than ƒ/1.2 or so). That can be very beneficial when shooting in dimmer lighting, especially important, as depth of field is extremely limited. The faster the lens, the more limited the depth of field when the lens is used wide open. With the superfast ƒ/0.95 lenses, you can concentrate the viewer’s attention on a specific portion of a subject through choice of focus point, while everything else in the image is thrown out of focus.

Fast lenses used wide open also produce interesting bokeh, or background (and foreground) blur. The very wide aperture combines with the lens’ optics and the number and shape of the aperture blades to produce the bokeh effect.

Something to consider is that on a DSLR or mirrorless digital camera, your superfast lens may not be as fast as you expect. At wider apertures—ƒ/2 and faster—the image sensor "wells" block some of the light, resulting in less light reaching the photodiodes than would be expected. (For full details on this phenomenon, go to Also, the thickness of the filter stack on the sensor can adversely affect sharpness if it’s different than what the lens was designed for, and fast lenses are especially susceptible. (Film cameras, of course, have no filter stacks; Micro Four Thirds mirrorless digital cameras have filter stacks of around 4mm, and APS-C and full-frame digital camera stacks are somewhere in between.) For more information about this from those who researched it, go to and look for the blog entries about "sensor stack thickness."

Why Are The Fastest Lenses Primes?

You’ll notice there are no zooms in our Superfast Lens chart. That’s because as the focal length increases, the diameter of the aperture must increase, too, to maintain lens speed. A 24-105mm ƒ/1.0 zoom would need an effective aperture diameter of 105mm at 70mm—that’s about four inches (not counting the lens structure surrounding that opening)—and would make for a bulky lens. And, if the designer went for a variable-aperture design, it would get slower as you zoomed to longer focal lengths; it wouldn’t be superfast at the long end. An ƒ-stop of 2.8 is a fast zoom, regardless of focal-length range (making that Sigma 200-500mm ƒ/2.8 all the more impressive—all 34.6 pounds of it!).

Lenses aren’t at their sharpest wide open, and the faster the lens, the more evident this becomes. Superfast lenses also tend to be harder to correct for various aberrations, and those aberrations and distortions tend to be most pronounced at the widest apertures. You can expect Leica’s $10,000 50mm ƒ/0.95 Noctilux-M to be sharper wide open than the much lower-priced ƒ/0.95 lenses, but it’s something you should keep in mind if you intend to shoot wide open. However, while most lenses are sharpest a stop or two down from maximum, an ƒ/0.95 lens stopped down two stops is faster than an ƒ/1.4 lens wide open!

Is F/1.4 Fast Enough For You?

While we’ve confined this article to the superfast lenses—those faster than ƒ/1.4—there are lots of ƒ/1.4 lenses out there, and ƒ/1.4 is still pretty fast. The ƒ/1.4 lenses are generally better all-around tools than the superfast lenses if you don’t need superfast apertures. And the best of the ƒ/1.4 lenses are amazing. The Zeiss Otus 55mm ƒ/1.4 and 85mm ƒ/1.4 are generally considered the best normal and short tele available, and the far less costly Sigma 35mm ƒ/1.4, 50mm ƒ/1.4 and 85mm ƒ/1.4 Art lenses rank right up there.

Also, note that few of the superfast lenses are AF. Conventional DSLR phase-detection AF may not be repeatedly accurate enough to nail focus when using lenses with such limited depth of field, and when doing selective-focus work, you really want to control exact focus placement yourself.

Rent To Own?

If you’re interested in superfast lenses, consider renting those that interest you before buying to see how you like the effects with your camera and shooting style. That way, you can see how sharp the lens is wide open, how its bokeh is and how well your camera’s AF system works with it (and how easily you can nail focus with it manually) before committing a large sum to purchase. If you can’t find superfast lenses for rent locally, rents most of those in the chart below.

A Bit About Depth of Field

One reason to use a superfast lens is to limit depth of field in the extreme.There are several ƒ/0.95 lenses available for Micro Four Thirds cameras, and these are much faster than any available from the camera manufacturers. But remember that the Micro Four Thirds "2X" lens factor applies to depth of field, as well as focal length: A 25mm ƒ/0.95 lens on an MFT camera is equivalent to a 50mm ƒ/1.8 lens on a full-frame DSLR or 35mm film camera in terms of depth of field. Exposure-wise, ƒ/0.95 = ƒ/0.95: If you shoot at 1/250, ƒ/0.95, ISO 100 with a 25mm ƒ/0.95 lens on an MFT camera, and 1/250 at ƒ/0.95, ISO 100 with a 50mm ƒ/0.95 lens on a full-frame camera, both images will have the same brightness, but the full-frame image will have less depth of field. The fastest lens available for MFT is the HandeVision IBELUX 40mm ƒ/0.85, which delivers depth of field equivalent to an 80mm ƒ/1.7 lens on a full-frame camera. That’s about as narrow a depth of field as you’re going to get with Micro Four Thirds.

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