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DrChris Dec 13, 2006 4:29 PM

I have a KM 5D and my longest lens is a Tamron 28-300mm. Will a 2x TC work well with that lens being that it's not very bright? I'll mainly be wanting to get closer to wildlife and such...outdoors only.

Also, how does a TC effect image quality? Is one brand any better than another?

Any thoughts?

eric s Dec 13, 2006 8:57 PM

I don't know that lens, what is the max f-stop/aperture?

Most AF systems will stop working when the largest f-stop is larger than f/5.6. If you use a 2xTC, then you loose two stops of light. That means that the lens would have to be f/2.8 to retain auto-focus after you put a 2x TC.

Also, they magnify any flaws in the lens. In other words - an ok lens will probably produce bad (soft) images with a 2xTC. A really good lens will probably produce "good" images.

Also, because of the higher magnification (600mm) camera shake will effect it more. So you'll need to hold the camera very steady or use a tripod (which would be my suggestion.)

As for brands, I generally recommend you get the one that is made by the lens manufacturer. But I would make sure that the TC is actually compatable with your lens. Some TCs have protruding elements that will hit the rear element of the lens unless it is designed to be used with a TC. I know that canon has this issue, so I wouldn't be surprised if others do as well. It lets them produce a better TC, but it limits which lenses it can be used on.


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