Focallength formula

In this picture, 55-200 on the left side is the range of the focal lengths available with the lens. The white line on the right side indicates the focal length currently set.

Myself, I’d order one now but I’m still thinking of going full-frame in a year or two so I’m hesitating. It’s so damn tempting however. If I had to repurchase my gear tomorrow, a Canon EOS 70D and this lens would be a killer combination for just $2000. Perhaps I’ll get this and hold off on a full-frame for a while!

Generally, lenses with a focal length of around 35 mm are called normal lenses, because they have an angle of view close to the human visual field. Lenses with a focal length shorter than this are called wide-angle lenses, and those with a longer focal length are called telephoto lenses. However, there are no strict standards for these terms. Use different lenses according to the subjects or images you want to shoot.

FOV tofocallength

On the other hand, if you use a fixed focal length lens, which does not have a zoom feature, you have to move in order to affect the composition. However, fixed focal length lenses are usually faster and have a wider aperture. They offer advantages in expression involving defocused backgrounds and the ability to use high shutter speeds in low-light situations, reducing image blur. In addition, they have superior rendering performance, so you enjoy excellent image quality that cannot be delivered by a zoom lens.

A picture taken with a 35mm lens on a camera with a full frame sensor, shot at f/2.8 and ISO 200, provides — in terms of depth of field and bokeh — a similar image as shot with the Sigma 18–35mm Art on a APS-C sensor camera with the same shutter speed, f/1.8 and ISO 100. Due to the difference in ISO is also full-frame relationship between cameras, and APS-C cameras wiped away a large part of the difference in signal-to-noise.

Focallength camera

What it does not have is optical stabilization (OS). This is a little less important at wide angles and fast apertures but it would have been an amazing edition. That said, it would probably push the price above $1000 so it may have been a wise choice by Sigma to keep it priced for the general market. I would suspect a second generation of this lens may have stabilization.

The other obvious negative is it’s size and weight which are inevitable given the specs. It comes in at a hefty 1.78 lb (811g). The zoom range is a bit limiting (28.8 to 56mm equivalent) but it could still easily replace a couple primes you’d otherwise buy and have to carry around and switch out on-the-go.

This comparison table by DxOMark says it all given it’s now the best performing APS-C zoom in their entire database of lenses. It sits above the Canon EF 24–70mm f/2.8L II USM and even my beloved all-white Canon EF 70–200mm f/2.8L IS II USM! That’s amazing.

One might think such a lens would be quite soft but early reviews attest to its sharpness and the lens measuring scientists at DxOMark have proof in the numbers. This is a real winner for Sigma and it’s earned my respect for what they can produce.

Focaldistance vsfocallength

UPDATE May 2016: Sigma now offers a telephoto zoom version of the Art series, the Sigma 50–100mm f/1.8 DC HSM Art ($1099). Get both and you’ve effectively got a prime lens for every focal length in the 27 to 52mm and 75 to 150mm range (based on Nikon 1.5x crop factor).

Let's check the focal length of your lens. The range of the focal length available with the lens is printed on the lens. For example, focal lengths from 55 mm to 200 mm are available with the SAL55200-2 in the picture below. Also, on the mount side of the lens barrel (near the camera body), you can see the mark for the focal length currently set. In the picture below, the current focal length is 55 mm.

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Focallength

This photograph captured the details of a sunflower with a macro lens. With a macro lens, you can get this much closer to your subject.

focallength是什么

What’s remarkable about this lens is its extremely large and constant maximum aperture. That small f/1.8 value is fantastic as it means a lot of light gets into the lens AND it continues to do so even as you zoom in.

Let me know what you think of the lens or if you plan to buy one. Find it online at B&H (they ship to Canada affordably but check PhotoPrice.ca).

Lenses are divided into two types: zoom lenses, which have a variable focal length, and fixed focal length lenses, which have a fixed focal length. Some zoom lenses are versatile enough to range from wide angle to telephoto by themselves. In addition to being useful for everyday shooting, these lenses are especially convenient for travel when you want to carry as little baggage as possible.

Focus distance

Most high-end constant aperture lenses are usually expensive and max out at f/2.8 or f/4. To have one that’s relatively affordable and has a constant max aperture of f/1.8 is literally unheard of. The suggested retail is $1160 but the promotional price is $800. At that price, it’s groundbreaking to say the least and it’s a game changer for those without a full-frame sensor camera.

Internal focusing and zoom means the lens doesn’t move in-and-out when you zoom or focus and the front element won’t rotate at all. This is ideal in that it’s more robust, won’t trap sand/dust/dirt and a filter or matt-box attached to the lens won’t rotate on you unexpectedly.

focallength中文

This photograph was shot with a fixed focal length lens. By setting the aperture to a small f-number, the background is defocused to a large degree. Macro lenses, which allow you to take close-ups by getting closer to a subject, are also fixed focal length lenses. Although many recent zoom lenses have a macro feature with a fairly short focusing distance, their performance cannot match that of a dedicated macro lens.

Sigma recently released an APS-C lens that rivals nearly all other zoom lenses I’ve seen in its range, the Sigma 18–35mm f/1.8 DC HSM Art. I haven’t tried it myself but I’m dying to try it on my Canon EOS 7D to see how it performs given the rave reviews.

The Canon mount version is available now but on back order (understandably) and other mounts are coming soon it seems. Below are links to the lens pages on B&H for each of the available mounts. You can be notified when it will be available.

The 9 rounded aperture blades appear to create pleasing and smooth areas in the out-of-focus areas we lovingly call bokeh. Here’s a video testing it out from f/1.8 to f/16 in a number of conditions:

Focal length is the distance from the center of the lens to the image sensor (focal plane), and each lens has a different focal length. Focal length is important because it determines the range of a scene you can capture (angle of view). As shown in the following photographs, the shorter the focal length is, the wider range you can capture, while the longer the focal length is, the larger distant objects appear.

The key thing to understand with this lens is that it’s not for full-frame cameras. The most popular and comparable option for full-frame shooters is a 24–70mm f/2.8 zoom lens. Since full-frame cameras have inherently shallower depth of field and better performance at higher ISO, having a f/1.8 constant aperture zoom creates a true equivalent for those of us with cropped-sensor cameras. As noted in some early reviews, full-frame shooters still benefit from a slightly broader focal length zoom range with 24–70mm vs. Sigma’s 28.8–56mm equivalent, but this really levels the playing field and does so affordably. I say affordable given Canon’s version of the 24–70mm f/2.8 is a whopping $2300 while Nikon’s “only” at $1900.