Quote Originally Posted by Athiril View Post
360mm Tele-Xenar f/5.5 for Portraits in 4x5"

I wouldn't want to go shorter unless I had no space to work with.
Depends if the OP has a field camera it probably doesn't take that lens. ESPECIALLY for portraits. He/She did say landscape and portraits.

Anyway, it's hard to answer, you already have a 180mm so if you want a nice portrait lens, you probably want longer right? So 300mm is better, but if it's a field, get the fujinon 300 C f/8.5 as it focuses much closer than other 300mm so bellows legnth will be much less of an issue.