Sigma 20mm F/1.4 DG HSM Art by Marc Alhadeff:
The Sigma 20mm F1.4 DG HSM Art (1000 euros) is a very good lens optically for a wide angle with fast aperture
Centre sharpness is excellent , and closed down to F4 corners are very good
The F1.4 allows for some unique effect for a wide angle that has no equivalent
However at F1.4 you get medium corners and field curvature is visible , so far from a perfect lens
The biggest issue is certainly its weight : 1 kilo
So if F1.4 is a must for you , Sigma is the way to go , otherwise other options are lighter and as (globally) performant
Sigma 24mm F/1.4 DG HSM Art by Marc Alhadeff:
The Sigma 24mm F1.4 DG HSM Art (850 euros) is an excellent lens that has no equivalent for Sony FE mount
Size and price remains reasonable and optical performance is excellent wide open with very good sharpness in real life and very nice blur effects for close subject
For landscape where you will close the aperture, corners sharpness is excellent as of F4
Highly recommended if you like this focal length
Sigma 35mm F/1.4 DG HSM Art by Marc Alhadeff:
The Sigma 35mm F1.4 DG HSM Art (800 euros) is a excellent lens optically
Excellent sharpness , low distorsion , low CA, better than Sony Distagon FE 35mm F1.4 Zeiss on this point
The Sony has still the edge in term of Color rendition and Aperture ring for video and most importantly in term of AF reliability
Unfortunately, the not reliable AF in AF-S is a big hurdle and you will need to stick to AFC. I hope Sigma can fix it with a firmware update or better quality control with other samples of this lens
If you don’t have the money for the Sony Distagon FE 35mm F1.4 Zeiss (1100-1500 euros) take a look at the very good Samyang 35mm F1.4 AF which has also a very good sharpness, fast AF (even if not as fast as Sigma and Sony) and reliable AF (better than Sigma)
Sigma 70mm F/2.8 DG Macro Art by Marc Alhadeff:
The Sigma 70mm F2.8 DG Art (550 euros) is a Macro lens offering excellent optical results with top sharpness, good bokeh, low CA, low distorsion at a very reasonable price. AF is on the slow side like any macro lens, and you will need to correct the lens fall off wide open (no Lightroom lens profile for the moment (July 2018). The Sony 90mm F2.8 macro does not do better in term of sharpness but well in term of ergonomics but it costs almost 2 times the price of the Sigma
New Sigma FE lenses:
Sigma 14mm f/1.8 for $1,599 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 20mm f/1.4 for $899 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 24mm f/1.4 for $849 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 35mm f/1.4 for $899 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 50mm f/1.4 for $949 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 70mm macro for $569 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 85mm f/1.4 for $1,199 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 105mm f/1.4 for $1,599 at BHphoto, FocusCamera, Amazon and Adorama.
Sigma 135mm f/1.8 for $1,399 at BHphoto, FocusCamera, Amazon and Adorama.