What an excellent point bojan.
I've been eyeing some of those old Pentax M42 style pentax lenses on ebay.
Mainly for bellows macro work (identifying late roman AE4 coins) but now I can see some other uses! I'd get a nice field with a 135 F3.5 perhaps. With less elements than their modern counterparts I should get more light throughput as well. Maybe bring it down 1 or 2 stops for sharpness as usual.
