Đánh giá sigma 12-24 f4 năm 2024

Note the shots above were focused at maximum aperture for each focal length, then shot increasingly stopped-down. This results in some focus shift at longer focal lengths that we'll demonstrate further down the page.

When comparing the two lenses in our real world tests we see that Sigma suffers in sharpness throughout nearly the entire focal range when the lens is focused wide open, but especially from 20mm to 24mm. At the widest end the Sigma is nearly on par with the Canon at 12mm in terms of sharpness and actually performs better with respect to chromatic aberration. As we mentioned above the Sigma's performance declines at and beyond 20mm, especially when compared to the Canon lens, and stopping down doesn't help matters. Although the DXO data suggests the Sigma should sharpen up in the center by F8 at 24mm, we believe we're not seeing this due to the Sigma's rather severe focus shift at longer focal lengths. DXO's findings are based off of selecting the optimal shot from series' of meticulously manually focused shots, and while both approaches have their merit, the results you'll achieve will depend on your focus method (more on this later).

In terms of corner sharpness the Sigma performs very well when compared to the Canon at 12mm with both lenses exhibiting about the same level of sharpness (the Sigma's a tad sharper on the left while the Canon's a bit sharper on the right). As the DXO data suggest, we see that the Sigma performs very well with respect to the handling of CA in the corners of the lens as well. At 24mm we see the Sigma's corner sharpness performance decrease a fair bit when it's shot wide open at F4, which agrees with DXO data. Once the lens is stopped down to F8, the corner performance improves and is nearly on par with the Canon lens shot the same focal length. But F8 brings with it more diffraction, and this shows in the softer center performance relative to the Canon at F5.6 (which is all the Canon needs to be stopped down to for optimal performance).

It's worth noting that the perceived peripheral sharpness in the Canon lens may be slightly decreased due to the rather extreme lateral chromatic aberration. However, ACR (and other forms of post processing software) will be able to remove the majority of it, thus removing the color artifacts and improving image quality.

Sharpness Summary

The Canon lens performs very well across all focal lengths, so well in fact that it often reaches its peak performance by F5.6, and becomes diffraction limited thereafter (on a 5DS R). It's a feat of engineering. That said, the Sigma turns in comparable, if not sometimes slightly better in our real-world tests, performance at the edges at its wider end. But the same can't be said for its central performance, where it falls behind at all focal lengths, be it 12mm, 14mm, 16mm, 18mm, 20mm, and 24mm. Sigma's parity (or lead, depending on your specific copy or the side of the frame you're looking at) in edge performance wide open at the wide end is lost at the tele end, where the Sigma must be stopped down to F8 to match the edge performance of the Canon at F5.6, albeit fall well behind in central sharpness.

We discovered that much of the drop - or lack of improvement - in central sharpness upon stopping down was due to focus shift due to the high levels of spherical aberration the Sigma lens exhibits (confirmed by LensTip). We briefly investigated how much better the Sigma could do when working around its focus shift problem by comparing shots focused wide open vs. stopped down at 24mm, below.

Focusing wide-open vs. focusing at shooting aperture

As you can see from the widget above, the Sigma 12-24mm had to be focused at the selected aperture in order to get maximum sharpness at the focused (central) point. However, maximizing center sharpness ended up costing corner sharpness, especially on the, right side. In other words, it was difficult to optimize for both center and corner sharpness with this lens.

It's not the first time we're seeing this sort of behavior (the venerable Nikon 14-24mm F2.8 exhibited ); however, it's fairly disappointing to a Canon shooter since all Canon DSLRs focus wide open, even in live view. A workaround is to switch into video mode to autofocus, since this mode stops down the aperture, or hold down the DOF Preview button while magnifying to manually focus at the selected aperture. If you're a Sony a7R II shooter you can get around this by using an electronic lens adapter (such as the Metabones Smart Adapter) that allows you to manually (or auto) focus at the shooting aperture.

The Canon lens, simply put, didn't experience these types of issues as evident in the real world comparison widget seen at the top of this page. It was able to produce images with excellent sharpness, even when focused wide-open.

Sunstar and Lens Flare

Sigma 12-24mm F4 Sunstar

Canon 5DSR, 16mm, 1/250, F18, ISO 100

Canon 11-24mm F4L Sunstar

Canon 5DSR, 16mm, 1/320, F18, ISO 100

Both the Sigma and the Canon exhibit very aesthetically pleasing sunstars. Subjectively, the Sigma lens was able to achieve more obvious sunstars by an aperture of around F10, while the Canon had to be stopped down further (F14-F16). That gives the Sigma a bit of an edge: getting sunstars at smaller F numbers helps limit the effects of diffraction. That said, once the Canon was stopped down to F16 or F22, its sunstars offered 'rays' that are finer and more defined in shape, as opposed to the broader rays of the Sigma. The sunstars on both lenses are very symmetrical.

Lens flare is handled fairly well by both lenses and neither exhibit extremely strong or displeasing flare, which is quite the accomplishment for a lens with this large of a front element.

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