Birds are tiny creatures who are easily scared. So, if you want to catch them, you need a long telephoto lens. The thing is, which one? if we pull the 500mm+ out of the equation (too big / expensive), the choice most photographers have is between the 300 L f4 ISand the 400 L f5.6. Both are about the same price but target different market.

Ask any wildlife photographers and they will tell you that you need at least and equivalent focal length of 400mm to catch any good bird pictures. So if you are shooting with a full frame camera, only the 400 L f5.6 will fill that requirement so you are set.

On the other hand, if you use a cropped sensor, both doors are still open and interesting. Should you get the 400 L f5.6 with an EFL of 640mm to get extra close to your target or should you go with the shorter lens and make up with better light sensitivity and IS?

Having shot many times with both lenses in many circumstances, I have found the extra range to be more important than IS and wider aperture since both of these can be compensated with higher ISO. On the other hand, you can’t get any closer without cropping, which is generally a big nono.

NOTE 1: if you are thinking about using the lens to shoot other subjects than birds and other small animals, you will be better serve with the 300 L f4 IS. It is more flexible and can be used for portraits, landscape, etc.

NOTE 2: if you are thinking about doing video, get the 300 L f4 IS. At such a long focal length, IS makes a huge difference in the end results.

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