In this Sony vs Sigma FE 135mm f/1.8 Lens Comparison Review Tony goes over the key differences that matter between these two lenses including size and build quality where the Sony has the clear advantage. Then Bokeh was tested and looked about the same quality overall. Next overall sharpness was tested and the Sigma appears to come out slightly ahead of the Sony, but the Sony had a higher hit rate when it came to autofocus accuracy. Next the contrast is tested using a backlit subject scenario and again the Sony comes out ahead.
A the end of the day the Sony is approximately $600 more and the Sigma and it will get the job done with pretty much the same image quality. What you are missing with the Sigma is the better build quality with a dedicated aperture ring and built-in buttons, plus a smaller size. Also the focus accuracy is noticeable better with the Sony as far as hit rate. What you get with the Sigma however, is way less of a dent in the wallet, slightly better sharpness, and a larger overall size.
The Sony FE 135mm f/1.8 GM lens goes goes for $1898 US @ BHPhoto | Amazon
The Sigma FE 135mm f/1.8 Art Lens goes for $1399 US @ BHPhoto | Amazon
We review the Sony 135mm f/1.8 vs the Sigma 135mm f/1.8. We compare sharpness, autofocus accuracy (with eye-detect AF), bokeh, and contrast in backlit situations. We also compare handling, including their size and weight.