I'm still trying to explore the advantages of the f1.4 vs f1.8. I know these are two different lenses and the Nikon 85mm f1.4G might be more appropriate but I do not have that lens.
Here is the size comparison to start with. The Sigma is definitely much bigger and heavier as what you would expect for a f1.4 lens.
Nikon vs Sigma 85mm by gqtuazon, on Flickr
Current price from BH photo as my price reference for the Nikon 85mm f1.8G is $496.95
The Sigma 85mm f1.4 HSM is $894.00 and compared to the Nikon 85mm f1.4G it is priced at $1,599. USD.
I have not done any extensive testing yet. The Nikon 85mm f1.8G appears to have no purple fringing whe shooting outdoor at f1.8. The Sigma tends to have this at f1.4.
AF appears to be very responsive in low light and both have focus override feature that I like compared to the older D lens.
I'll do some more testing on sharpness but I am certain that they will be very close by f2.8. I wish I have my D800E to test them but the D3s will do for now.
So, one thing that surprised me with my testing is the difference that each lens provides at higher ISO.
With the camera mounted on a tripod, M mode, Auto ISO to 6,400, 1/400, matrix metering.
Sigma Aperture ISO
f1.4 2,800
f1.8 4,000
Nikon f1.8 4,500
Here is the size comparison to start with. The Sigma is definitely much bigger and heavier as what you would expect for a f1.4 lens.
Nikon vs Sigma 85mm by gqtuazon, on Flickr
Current price from BH photo as my price reference for the Nikon 85mm f1.8G is $496.95
The Sigma 85mm f1.4 HSM is $894.00 and compared to the Nikon 85mm f1.4G it is priced at $1,599. USD.
I have not done any extensive testing yet. The Nikon 85mm f1.8G appears to have no purple fringing whe shooting outdoor at f1.8. The Sigma tends to have this at f1.4.
AF appears to be very responsive in low light and both have focus override feature that I like compared to the older D lens.
I'll do some more testing on sharpness but I am certain that they will be very close by f2.8. I wish I have my D800E to test them but the D3s will do for now.
So, one thing that surprised me with my testing is the difference that each lens provides at higher ISO.
With the camera mounted on a tripod, M mode, Auto ISO to 6,400, 1/400, matrix metering.
Sigma Aperture ISO
f1.4 2,800
f1.8 4,000
Nikon f1.8 4,500