Originally posted by dandog i would advise doin alot of research on the net regarding sigmas you like.
I would emphasize that!
Originally posted by dandog although people have said they can be quite soft at 500mm.
I cannot rule out, that there are "soft" copies of the Sigma 50-500 "out there". But generally this is an "urban myth". The Bigma gets soft at 500mm if the focus is not spot on. Look through the many images posted on this site and on others and you'll get a good idea of what that lens is capable. And it can be tack sharp with good contrast even wide open at 500mm, if used properly.
But using a 500mm lens is not easy and results usually are not good at the start. We have had a lot of threads on really long glass over the last months.
You may find a lot of info in the thread:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/55946-300mm-pl...ng-lenses.html Originally posted by dandog then you need to factor a tripod into the money.
do not get a cheap tripod.
That is VERY true. A good tripod and head is a must for long glass. IIn some cases even a good monopod provides already a notiecable improvement in IQ.
Originally posted by dandog there are a lot of good deals on the used market so dont dismiss it fully.
i recently bought a sigma 100-300 f/4 with a 1.4 teleconverter.
to get over 400mm,and the quality is alot better than your 50-500-150-500 range.
I sure concede, that the Sigma 100-300/4 is an excellent lens. Whether it is better at 420mm (the max. with a 1.4x tc) than the Bigma or any other dedictadet longer lens, I don't know.
What I know is, that it is very hard to actually see these potential differences at these long focal lengthes, as there are other limitations to IQ with these long lenses, than slight resolution or contrast differences. Using long lenses, as I wrote above, needs practice. It also needs the right circumstances and all in all, fine differences in lens quality will play only a minor part. Ofcourse I am not writing about crappy lenses.
Ben