A 28mm fast lens is probably one of the first prime lenses a self-respecting photographer will want to own. So I can see Sigma's new 28mm f/1.4 DG HSM Art lens being popular with budding photographers.

If they have a full-frame interchangeable-lens camera (ILC), they will get the full 28mm focal length with this lens. But if it is a crop-sensor ILC, the resulting focal length will be 42mm (for Nikon and Sony ILCs) or 44.8mm (Canon).

When I hold this lens for the first time, I am pleasantly surprised that it is not as heavy as I had thought. At 865g, it is relatively light compared with the excellent but heavy (1.2kg) 40mm f/1.4 DG HSM Art lens.

In terms of build, it is what you might expect from the Sigma Art series - nice and sturdy.

The lens structure is said to be resistant to dust and water splashes. Plus, there is a water-and oil-repellent coating on the front lens element for shooting in challenging conditions.

The lens has only one autofocusing (AF) switch - sited on one side of its exterior. A large rubber focusing ring allows easy manual focus when needed.

The interior houses 17 glass elements arranged in 12 groups, including two F Low Dispersion and three Special Low Dispersion glass elements. This arrangement is said to minimise distortion and chromatic aberration.

For this review, I use the Canon EOS 7D to test the lens' AF speed and Sony's 42.4-megapixel a7R II (using Sigma's MC-11 E-mount converter) to test the lens' optical quality with high-resolution still images.

In terms of AF, the lens - when used with the 7D - is swift in most situations, getting a focus lock in less than a second even under dim lighting conditions. When used with the a7R II, the AF suffers a little. At times, it took around two seconds to secure a focus.

Overall optical quality is impressive. Centre sharpness is a little soft at its maximum aperture size of f/1.4. But this is expected when shooting with large aperture sizes such as f/1.4 or f/1.8.

However, when the size is reduced or stopped down to f/2.0, centre sharpness is excellent. Edge sharpness is equally stellar at f/2.0 and remains pristine through to f/8.0.

Vignetting is clearly visible from f/1.4 to f/2.8. It disappears when the aperture is stopped down to f/4. In addition, I do not notice much chromatic aberration and barrel distortion throughout the aperture range.

Bokeh, or out-of-focus areas of an image, looks pleasing and natural - not something smartphone cameras can replicate.

The lens lacks a built-in optical stabiliser (OS), which is a downside. And while you might think you do not need one as the aperture is so huge, the OS will come in handy when you stop down the aperture.

In addition, its price is understandably expensive for a prime lens of this stature and hence it is a hefty investment.