Sigma 18-35 f/1.8 poor image quality

Question

I recently bought for my D3300 two new lens. The Nikon 50mm f/1.8 and Sigma 18-35mm f/1.8 Art. As I expected, due to specifications and measurements in DXOMark, the 50mm lens is awesome. A lot more sharper. A lot more realistic colors. But when I mounted the Sigma, the expectations were also high as for the other new lens, but actually I was very disappointed from the image quality of the Sigma.

DXOMark measurements shows that the Sigma, mounted on that body has to have a lot more sharper images. They score the sharpness as 17 P-Mpx while my kit lens (18-55mm f/3.5-5.6G VR) is scored 7 P-Mpx.

I shot a lot of test images yesterday to compare the images from both lenses - the Sigma and the kit lens. There is no diffirence at all. Images are all the same having a poor quality (Subjectivly poor, considering the quality of the prime 50mm). I know that the prime is prime and better... but let me explain bellow.

I make some experiments. For example when I shoot with the 50mm lens, and then increase the saturation or shadows or black to see how much of artefacts, noise and and etc occur in the image (I tried to ruined it) the 50mm is amazing. The colors, being over saturated are still realistic, while with the kit lens they are very bad (e.g. blue become more cyan and etc..)

When I made same experiments with the Sigma, comparing it with the kit lens, the results of all images were absolutely equal for both lenses. No difference in the images. I cant say which image is taken with which lens. I dont like the images from the Sigma, while the images from the Nikon 50mm prime are awesome.

By all the measurements in the DXOMark, and all reviews that I read and viewd for this Sigma lens, it has to be very good lens, very sharp and compared to the kit lens it has to be really a lot more better lens. But reality shows that this is not that way.

Is it possible the lens to be defected? Have any one tested it and compared the images? Is the new Sigma is overrated? Becouse it cost 5 times more than the kit lens, but the quality is not better at all.

To be fair only at the 35mm end Sigma shows a little more sharper images form the kit lens. But at the near end only.

Answer 1

Testing optical performance of lenses requires knowledge and an optical laboratory. Subjectively, looking at the results obtained via the images you have captured, which may raise your index of suspicion about the performance of a lens so tested; may only point you in the general direction of disappointment with performance. In general terms, it is usually the case that a prime lens will outperform a zoom lens.

The large aperture zoom will have had to sacrifice some aspect of lens performance in order to achieve f/1.8 as a maximum aperture. I don't know the lens nor do I pay much attention to numbers published. Test results may give you a guide as to what to expect but they are usually results obtained under a specific set of conditions by one reviewer. The general applicability in real life situations may not hold up. Try to test lenses which you want to buy; first. Hire them for a week and see how they fit with your own techniques and equipment. This is far more useful than reading lab numbers.

Possibly your copy of the lens is faulty and informing the vendor is the first step in initiating a remedy. You can still hire an identically specified lens and see if it performs to your expectations. Check lens reviews on technical sites and try to assess the lens you want to buy from several different impartial technical reviews. If you still cannot resolve the issue, reject and return the lens and wait until you can find another lens and specification, which will suit your future needs.

The zoom lens can be poorly assembled and poor element collimation would produce symptoms like you have described. It is not your job to test your purchase. You can return it as unfit for the purpose it was sold. If a second and or a third lens produces similar results, you may have to accept that this particular lens cannot perform to your expectations. It may be time to rethink your lens collection. Given that you can already cover the focal lengths the new zoom lens covers, you may consider buying a lens which shows a different perspective.