These photos were taken with a 75-300mm Nikon zoom at 300mm. As you can see this focal length is hardly adequate for these critters. The grizzly was actually closer then other sightings and so was the caribou. You can not and should not try get any closer to these animals. At least a 600mm is required, unaffordable big bucks. A teleconverter can be used very successfully, however. I used fast film given the long focal length, usually with no time to set up a tripod and cloudy overcast. I did not have it on this trip, I do now as a result of it, the Nikon 80-400 VR on a Nikon D100 will do very nicely giving you the 600mm due to of the digital crop. I used a wide angle zoom 18-35mm most of the time for landscape photos.