I have an older Brass Dallmeyer Rapid Rectilinear 16x18 ( about 25") it is F8 and it will fit on a 5 1/4 x5 1/4 lens board, but barely. Its not actually a portrait lens but it very well could be used as one. Or a little more modern lens would be something like a Wollensak 14 1/2" Verito which would probably also work well.