Originally posted by JamesAus I've found a 300mm f4 lenses, but it's $3,500 so way out of my price range unfortunately.
HI James, I only yet read through the whole thread and will add my ideas:
Firstly I would go with a zoom lens anytime for that kind of shooting. You cannot walk nearer to the polar bears but have to stay onboard your Tundra Buggy (which is a sensible notion, by the way). So something like the Tokina 80-400 or the Sigma 150-500 or the Bigma, you're already considering would be my first choice. I don't think the limiting factor for the image quality will be the zoom.
I have the old (first generation) Tokina 80-400. It is okay, but nothing to rave about. As I use mainly fixed focal length lenses, it sees very little use and will be off to ebay soon. I will, when I got rid of some more lenses, buy a Bigma myself, as after all what I have read about actual experiences, it seems to be a good choice. I hope this will be used more often than the Tokina.
Secondly: for that particular occasion, forget the tripod. Either use a saddle-bag style bean bag or a window clamp for the camera. The Gorilla pods are nowhere rigid enough to support such a long lens. A bean bag will also allow better camera movement, when following the bears.
You could use a monopod and cobble together a windows mount - perhaps based on the ubiquos Manfrotto studio clamp -, which would allow fixing the monopod to the window or another rigid part of the Buggy. That would give you the option, to rest, without letting go the camera over board.
I would personally prefer the bean bag for shooting out of the Tundra Buggy, otherwise a lightweight tripod might serve you well for other shooting opportunities (outside the Buggy) during that trip.
Thirdly: in cold conditions, use a carbon fibre tripod. It will cause less trouble for your hands, if you touch it... Not only tongues and lips can freeze to cold metal, fingers can so, too. I am speaking from experience... The bean bag is ofcourse a very secure device in cold conditions.
Fourth: I normally use lightweight, finger gloves made from stretch material (don't know, either The North Face or Lowe) for shooting. They are thin enough, that you can use the camera normally, but warm enough for most conditions. If it is really cold and windy, I prefer a combination of mitts with finger gloves. You can fold back the mitts, made of wind resistant GoreTex Windstopper and than use the thin finger gloves for shooting. If the fingers get cold, just pull the mitts over them again. The particular modell I use is made by Eska (a specialist gloves supplier from Austria) and it also sports the typicall small hole for the right index finger in the gloves, which hunters prefer, to pull the trigger with more "feeling" in their finger, than any glove can provide. Any good outdoor sports shop should provide a selction of those. I can highly recommend the Windstopper material, because it really keeps wind (and wind chill) out. That means, the gloves or mitts can be made lighter and thinner, without compromising warmth.
These are my recommendations after several tours through Iceland and in the Norwegian winter.
Ben