06-13-2013 12:40 PM
This mean if you have a f4 lens, a extender will reduce the amount of light to the sensor by 2 full f stops. This is like reducing your aperture to f6. (making a smaller aperture allowing less light to the sensor) The extender does magnify the output of the lens..
Also, as a point of clarification: Autofocus won't necessarily not work. It will be slowed in all situations (to 25%). Whether it works at all is dependent on the camera body and lens combination.
06-13-2013 04:26 PM
Something else to keep in mind is that on your crop sensor a 200mm lens will be the equivalent of 320mm, and a 300mm will actually be 480mm. When I started out I used the 70-300 on the 60D for a lot of wildlife shots. Sometimes it will come up short as others have mentioned but worked 80% of the time. The 70-200 2.8 is a great lens but you will lose autofocus on the 60d when combined with a 2.x teleconverter (not an issue with the 5d). My favorite lens for wildlife right now is the 100-400L and you can pick those up used for about 1200.
06-30-2013 09:08 AM
For wildlife photography, I have been generally happy with a 420mm f/5.6 fixed lens system (300mm f/4.0 L IS USM + 1.4x converter) with a monopod. On the 60D it is light enough to carry on long treks in the field. I use a monopod. The past two weeks while traveling I have been using a borrowed Canon 100-400mm l/4.0 IS USM zoom. It is MUCH heavier, but it has the great advantage of being able to shoot large subjects such as herons and alligators at close range without cropping. Worse, I did not have my monopod. It took many great photos, although I had trouble getting sharp focus on small subjects such as songbirds at 20-30 feet range. Using center point focus, it seems that the focus area is larger or more diffuse than with my 420mm system, so I had many bad out-of-focus outtakes in these circumstances. It seemed to focus on the foreground or background, or intervening vegetation that would not have been a problem with the 300mm_1.4 extender. It also seems not to focus as closely in the macro setting. BTW, I always carry a point-and-shoot for landscape and macro shots when needed. You may see my more recent shots and compare them with past ones on my FLICKR pages.