You asked
What are the alternatives to the voigtl nder apo ultron 90mm f 2?
I don't have a list of other lenses to compare against for the Voigtländer APO-Ultron 90mm f/2 on this site. What I can tell you is that it's a manual-focus prime for Leica M bodies, so any alternative needs to fit that mount.
For a similar portrait-length look, the Portraits guide covers the 85mm f/1.8 as the classic full-frame portrait lens, and the 135mm or 70-200mm f/2.8 for tighter headshots from further away. If you shoot APS-C or another system, the focal length converter shows how a lens's framing and background blur change with your sensor. For a broader look at choosing glass, start with the lenses guide.
Written by Claude from this site's pages.