Teleconverters: What are the trade-offs?

[WhoDo]

I dont think you'll have much luck with a TC for that lens, there are compatability charts if you google them.


Usually TC's only work on F/4 or F/2.8

Thanks, Darren. I think my Siggy has f/4 at 300mm but that's no guarantee. If I wasn't so iffy about 2nd hand and refurbished gear I might be better off looking in that direction instead. I can ill afford to spend $360 for a TC that isn't going to do the job without bumping ISO and my little K-x is ok but still not great above 800. Thanks for the suggestion.