Hi all! I have a 5D3, and I just bought the new 100-400L IS II lens.

[LisaQ]

Hi all!  I have a 5D Mark III, and I just bought the new 100-400L IS II lens.  I have an EF 2x III Extender, and I can't get the lens to auto focus when using the extender.  Can someone help me with this?

[Skirball · Accepted solution]

Using a 2X extender doubles your minimum aperture.  The aperture of the 100-400 is 4.5 - 5.6, so if you double that it's 9 - 11.  The maximum the 5d3 can autofocus is f/8, and I believe that is only the center point (and with the firmware?  I don't remember). 

Long story short, no AF with the 2X.   With 1.4x the center point should work.

[Skirball · Accepted solution]

Wise choice.  In general, most find that the 2x diminishes image quality too much for their liking.  1.4x is usually better regarded.  From what I've read, it's gotten good results on the 100-400 II with the 5d3.

[ebiggs1 · Accepted solution]

LisaQ,

I am going a little further and say even the 1.4x extender is going to be problematic.  You are transforming the lens into basiclly an f8 560mm.  The camera will still struggle but it will do it.

Most people use their zoom lenses at the long end is why I say this.  Because why would you put an extender on a lens that already has most of the focal lengths without it? (100mm to 400mm vs 140mm to 560mm?)

Another concern is 560mm at f8 is going to be a trick to hold and get sharp photos.  Yes, it can be done but you will need practice in hand holding.  Or, better yet, get a tripod.

As a general statement I don't recommend folks buy or use tele extenders at all.  But if you must, only on lenses that are f2.8 or faster.  Another suggestion, if I needed a 400mm lens that could get me 560mm cheaply, I would prefer the EF 400mm f5.6 L prime lens with the 1.4x II extender.  It offers several advantages.  One being it is much lighter.

Good luck.

[ebiggs1 · Accepted solution]

LisaQ,

Also another point most, if not all, don't realize is when you put a 1.4x (or 2x) extender on any lens you multiply everything.

Yes, the focal length and that is nice but you also magnify all the bad, too.  So it becomes 1.4x (or 2x) times harder to use since you have to become 1.4x (or 2x) times better.  Shake, blur, accurate focus, etc, everything.

[Skirball · Accepted solution]

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@LisaQ wrote:

Thank you for your input.  You make a great point.   Much to think about!

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I recommend not spending too much time thinking.  Pick up the 1.4x, and give it a try, it's peanuts compared to a 100-400II and 5d3.  Yes, there are limitations and hurdles to extenders, but plenty of people use them with great results.  There's only one way to find out if it works for you.

[RobertTheFat]

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@LisaQ wrote:

It's the hawks that have made me want one.  They're hard to get close to.  Even if it helps a little, I will be glad.  

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Several years age my wife was in the street in front of our house when a huge red-tailed hawk landed on the pavement about 20 feet away. He looked around for a minute or two, then took off again. Did she have her camera with her? No, and she obviously didn't dare run in and get it, for fear of scaring the hawk away. Oh, well ...