Not sure about the Voigt, but I had the Nikkor 20/3.5 AI, 20/4 AI and the 20/2.8 AIS and for me the UD is the clear winner with regard to colour, bokeh, distant, has less distortion and is therefore useful for a lot of applications and subjects. But these are of course personal preferences. perhaps Buddy has experiences with the other lenses?
I completely missed this post. Will try to make good on that now.
In a non-scientifical comparison between the 20mm f3,5, the 20mm f4, the 20mm f2,8 Ai-S and the 20mm f3,5 Nikkor-UD the results showed that between the copies tested:
The 20mm f3,5 Nikkor-UD has the highest centerresolution and sharpness
The 20mm f3,5 Ai has the highest flare resistance
The 20mm f2,8 Ai-S has the highest corner sharpness
The focal plane of the 20mm f3,5 Nikkor-UD is strongly curved. When used well you can get images with a sharp foreground, a sharp subject and sharp corners wide open.
The 20mm f3,5 Nikkor-UD has light falloff towards the corners, but less then the 20mm f3,5 Ai and the 20mm f4 Ai and less then the 20mm f3,5 Voigtlander.
The voigtlander comes closest to the performance of the 20mm f2,8 with the exception that it suffers more from CA and has quite a color cast towardswarm/red/orange.
The 20mm f3,5 and 20mm f4 Ai suffer strongest from barrel distortion. I believe the 20mm f2,8 Ai-S was slightly ahead of the 20mm f3,5 Nikkor-UD in this regard. The Voigtlander 20mm f3,5 is quite bad in barrel distortion as well.
Now on to first hand experience, I owned the 14-24 f2,8 AF-S zoom Nikkor. Bought the 20mm f3,5 Nikkor-UD to save space when I didn't need 14mm and here are my personal findings:
The 14-24mm f2,8 AF-S Zoom Nikkor is better from 14-19mm and better again from 21-24mm. It also performs better then the UD Nikkor between f2,8 and f3,4.
But at 20mm and f3,5 it only beats the UD Nikkor in light falloff.
I couldn't find any flaws in regards to sharpness in the UD Nikkor on the 36 Mpix D800. The center is sharp and the lens appears to outresolve the D800 sensor there with ease.
Stopping down does little to increase the center sharpness. But stopped down to f8 the edges and corners sharpen up considerably.
After 6 months of using the UD Nikkor I sold my 14-24mm zoom. The one wide angle Nikkor that positively appears sharper then the UD Nikkor (sharper then sharp) is the 16mm f3,5 Fisheye Nikkor.
