autofocus with the Canon 2X extender?

[Wendy Kates]

Hi all,

I have the Canon 7D Mark II and the 300 f/4 lens. Usually I use the 1.4 extender with it, but for situations in which I need additional reach, I wondered if the 2X extender will autofocus with that setup? If so, will it only autofocus at f/8?

Thanks,
Wendy

[John Flynn]

The 7D II will autofocus with the 300 f4 and a 2x. That being said it will be pretty slow and BIF will be pretty difficult. I've found personally that resolution does not increase significantly with using 1.4s on f4 lenses and cropping vs. 2x unless the light is good and you can keep the ISO relatively low. If you are taking pictures with a cloudy sky with a camera that doesn't do as good as the FFs in low light the difference will be neglible in terms of increased resolution. If you do decide to go with a 2x definitely get the series III TC. While the chip won't help your AF because the 300 f4 is an older lens, the series III has improved optics.

[John Flynn]

If I were you I would save the money and look to buy the 100-400mm or a 300mm 2.8. I looked at www.the-digital-picture.com for the 300 f4 with a 2x on it and it's pretty bad. I don't think the 300 f4s optics are designed to handle the magnification of a 2x. The 400 5.6 does pretty good with a 1.4x on it which would give you similar range as the 300 f4 with a 2x on it at a lower price point but you'd lose is and would not have the versatility of zooming like the 100-400m and you'd lose the close focus abilities of the 100-400mm or the 300 f4. It's also worth noting that a 1.4x won't work with the old 100-400mm.

[Doug Brown]

You might also consider the new Sigma 150-600 Sport. It'll give you extra reach at a relatively reasonable price, and is optically excellent. Also you'll have a maximum aperture of f/6.3 at 600 mm, 2/3 stop brighter than the 300 f/4 with a 2x.

[Andy Goris]

Wendy,
To answer your question, "I've heard it will only autofocus at f/8", the answer is, you can use any aperture you want to take the picture. All cameras use the largest aperture during focus, independent of what aperture you take the picture at. The aperture snaps down after focus lock. This means there is an advantage to buying an f/2.8 lens, even if you never take a picture with an aperture bigger than (i.e. f# smaller than) f/4 . The extra light and extra baseline (width of the lens) helps the camera focus very fast. The higher end Canon cameras can only autofocus with lenses that have apertures equal to or larger than f/8 (f# equal or smaller than f/8). This may be where you heard that statement. If you put a 2X on an f/5.6 lens, you effectively have and f/11 lens and the camera won't be able to autofocus in normal (phase focus) mode. You can always focus in live-view mode no matter what the largest aperture is (smallest F#). But getting back to your question, with the 300 f/4 and a 2X, you can use any aperture setting you want for the picture itself and the camera will focus. Now, I think (maybe someone can confirm) that the 7D Mark II has the same limitation as the two cameras I own, the 5D Mark III and the 7D original version. When your largest aperture is f/8 (which will be your case), you can only use the center focus zone. For birds I've never found this to be a problem. I have a friend that shoots with the 300 f/2.8 and a 2X extender III and gets good results.