Yesterday I picked up a used Rokinon 80-200 F4.5 with a pentax K mount, manual, for 10.00. I didn't notice until I got home that it is stuck wide open. Is it worth holding onto at that point? Although I am still learning my shooting technique and photographic style, very rarely do I go above 6.5 or so. My initial intention for this lens is to try my hand at railroad photography. I do have a 50mm prime, but it would be handy to have something longer.