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      07-12-2011, 08:04 AM   #33
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Originally Posted by UdubBadger View Post
ah, ok. That makes a bit more sense. So I will need to at least swap f/4 for a 2.8 to get the f/5.6 with the 2x.

or i can just keep the f/4 and get the 100-400.

This might help you: [linky]

The 100-400mm is sharper at 400mm f/5.6 than the 70-200mm at 400mm with a 2.0x TC. That being said, unless you constantly shooting for wildlife (like Dave), I recommend the 70-200mm since it's much more versatile (especially on a full-frame). You can use it for portraits, etc.

The only reason I didn't get the 70-200 f/2.8 IS II is because it's insanely pricey compared to the 70-200 f/4 IS, and has essentially the same sharpness. I also didn't need the extra stop for nearly twice the price and weight.

Originally Posted by UdubBadger View Post
hahaha, yeah it makes sense. maybe the 2.8 is a better choice though since I could run it on my 40D and use the 1.6x crop to give me some more zoom on it.

Would that work with the 1.4x converter? Does it change the f stops like the 2x?
Yes. With the 1.4x TC you lose 1-stop, and with the 2.0x TC you lose 2 stops. You'r aperture needs to be at least as fast as f/5.6 for AF to work on your non-1 bodies. The 1-bodies can work with an aperture at least as fast as f/8. That's why you can use a 100-400mm with a 2.0x TC with a 1D or 1Ds and still retain AF and have the cheapest 800-1040mm equivalent focal length.

By the way, another important thing to note is that a 1.4x TC results in a 25% decrease in AF speed, and a 2.0x TC results in a 50% decrease in AF speed. Usually people don't realize that when buying TCs.

Originally Posted by The1 View Post
but also remember, a 200mm is still a 200 mm on a crop or a full frame, it's just the image is cropped. It's easy to forget i find.
Although that's true, you have to have a reference system, and that is the 35mm equivalent focal length. So, a 200mm lens on an APS-C is essentially 320mm equivalent. It's assumed to be cropped.

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