[LabRat87]

You don’t mention what camera system you are using,
Mick.

I'm use either a pentax k1000, or OM-1.
May other concern was weight, as I've have a 2x tele, and a zoom for the om1. its alot of length and weight to hand hold.
The image becames quite a bit darker with the tele on; Prob has to do with the F-stop increase right???

Also i'm just shooting birds right now, and my 70-210 zoom works alright, there are times i just can't get close enough. Hence, my interests in a 500 Cat lens, compactness, and more magnification ( i learned some new terminology)

Thanks for all the advice.