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FORUMS Canon Cameras, Lenses & Accessories Canon Accessories 
Thread started 06 Feb 2018 (Tuesday) 14:13
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Canon Extender II

 
00derek
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Feb 06, 2018 14:13 |  #1

With the Canon Extender II (is there also a III?) does the 100-400 USM II lens lose autofocus only at 400mm? or is it >350, >300mm or what...?

Thanks




  
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Bassat
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Feb 06, 2018 14:28 |  #2

AF is camera dependent. What body are you using?


Tom

  
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Choderboy
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Feb 07, 2018 01:17 |  #3

100-400 f4.5-5.6. So with 2xTC its 200-800 f9-f11.
No Canon body will AF at f9 using CDAF, ie viewfinder.


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joeseph
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Feb 07, 2018 02:53 |  #4

00derek wrote in post #18557872 (external link)
With the Canon Extender II (is there also a III?) does the 100-400 USM II lens lose autofocus only at 400mm? or is it >350, >300mm or what...?

Thanks

the 100-400mm has a variable max aperture, meaning at 100mm it can open to f/4.5, and at 400mm it can only open up to f/5.6 (which lets in less light)
With diminishing size apertures, at some point, there isn't enough light getting to the camera to operate the AF reliably so there is a limit set in software.
Some cameras are more sensitive than others so it is body-dependent where this limit is.

my 100-400mm (mk I) is f/4.5 between 100mm & about 125mm, f/5.0 between 125mm & 260mm, and f/5.6 between 260mm and 400mm.
Don't know if the 100-400mm mk II has the same changeover points.


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Bassat
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Feb 07, 2018 03:25 |  #5

Choderboy wrote in post #18558287 (external link)
100-400 f4.5-5.6. So with 2xTC its 200-800 f9-f11.
No Canon body will AF at f9 using CDAF, ie viewfinder.

Nobody said 2X II. OP is using a TC (version II, we don't know which one) with a 100-400L II.


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Feb 07, 2018 03:42 |  #6

Bassat wrote in post #18558318 (external link)
Nobody said 2X II. OP is using a TC (version II, we don't know which one) with a 100-400L II.

My bad.

So the answer is not at all with 2X, yes with 1.4X and bodies: 1 Series, 7D2, 80D, 5D3 and 5D4.
Further, with 1.4TCII, AF is centre point with surrounding assist points while 1.4TCIII provides more points, depending on body.

All above regarding CDAF, ie viewfinder.


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apersson850
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Feb 07, 2018 15:48 |  #7

joeseph wrote in post #18558308 (external link)
the 100-400mm has a variable max aperture, meaning at 100mm it can open to f/4.5, and at 400mm it can only open up to f/5.6 (which lets in less light)
With diminishing size apertures, at some point, there isn't enough light getting to the camera to operate the AF reliably so there is a limit set in software.
Some cameras are more sensitive than others so it is body-dependent where this limit is.

This is wrong.
First, AF characteristics are determind by the smallest maximum aperture the lens has, i.e. in this case f/5.6. Hence it of no importance that the lens changes its max aperture when you zoom. It will not change the AF performance.
Second, it's not the amount of light that's entering the lens that's the limit. It's the diameter of the opening that sets the limit. For accurate focusing, the light rays coming in on one side and the other of the lens have to have a certain separation. High precison focus requires a larger separation, and thus freguently requires f/2.8 or better. Ordinary focusing accuracy usually requires f/5.6, although several of the later camera models will provide at least some AF operation even at f/8.


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Feb 07, 2018 17:17 |  #8

So which TC is it? 2X or 1.4X

there are 3 version of each, the MKIII will give the best AF results with the gen II lens and a modern body.

Don't bother with a 2X of any "Mk" on the 100-400mm.

1.4x II will work on some bodies, but will limit the number of usable AF points.

1.4X III will work best on the most modern bodies.


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Bassat
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Feb 07, 2018 18:40 |  #9

apersson850 wrote in post #18558789 (external link)
This is wrong.
First, AF characteristics are determind by the smallest aperture the lens has, i.e. in this case f/5.6. Hence it of no importance that the lens changes its max aperture when you zoom. It will not change the AF performance.
Second, it's not the amount of light that's entering the lens that's the limit. It's the diameter of the opening that sets the limit. For accurate focusing, the light rays coming in on one side and the other of the lens have to have a certain separation. High precison focus requires a larger separation, and thus freguently requires f/2.8 or better. Ordinary focusing accuracy usually requires f/5.6, although several of the later camera models will provide at least some AF operation even at f/8.

This may or may not be wrong. I can't tell because the first half of it makes no sense. AF is not determined by the smallest aperture; it is determined by the largest aperture. F/5.6 is by no means the smallest aperture ANY canon lens has at ANY focal length. I do agree with you that MAX aperture changes as you zoom. In all likelihood so does the smallest, but that has nothing to do with anything.

Please explain the separation you refer to. I don't understand and have never heard that. High precision focus depends on two things: amount of light, and amount of contrast. The fact that different sensors can have different configurations at various apertures means nothing if you try to focus in the dark. A dual cross f/2.8 focus point can't see any better at -6EV than a horizontal-only f/8 point.


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Bassat
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Feb 07, 2018 18:42 as a reply to  @ CyberDyneSystems's post |  #10

Canon claims my 100-400Lc/80D/1.4X II combination can AF with the center point. The reality is that, for all intents and purposes, it does not. Never tried 1.4X III.


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John ­ Sheehy
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Feb 07, 2018 19:26 |  #11

Bassat wrote in post #18558905 (external link)
Canon claims my 100-400Lc/80D/1.4X II combination can AF with the center point. The reality is that, for all intents and purposes, it does not. Never tried 1.4X III.

That's strange, because my 100-400L "C" AFes very accurately with all AF points with a Kenko Pro 300 DGX 1.4 on my 6D, which doesn't even support f/8 officially. Not real fast, but very accurate. What do you mean by "it does not". Does it hunt too much?




  
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Bassat
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Feb 07, 2018 21:29 |  #12

John Sheehy wrote in post #18558928 (external link)
That's strange, because my 100-400L "C" AFes very accurately with all AF points with a Kenko Pro 300 DGX 1.4 on my 6D, which doesn't even support f/8 officially. Not real fast, but very accurate. What do you mean by "it does not". Does it hunt too much?

I mean that it is way too slow to be of any use for moving targets, and way too inaccurate to use for stationary targets. As in: may as well not have it. It tries, it even locks and beeps, but the targets are not in focus. As in: it doesn't work.


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joeseph
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Feb 08, 2018 02:38 |  #13

apersson850 wrote in post #18558789 (external link)
This is wrong.
First, AF characteristics are determind by the smallest aperture the lens has, i.e. in this case f/5.6. Hence it of no importance that the lens changes its max aperture when you zoom. It will not change the AF performance.
Second, it's not the amount of light that's entering the lens that's the limit. It's the diameter of the opening that sets the limit. For accurate focusing, the light rays coming in on one side and the other of the lens have to have a certain separation. High precison focus requires a larger separation, and thus freguently requires f/2.8 or better. Ordinary focusing accuracy usually requires f/5.6, although several of the later camera models will provide at least some AF operation even at f/8.

I'm always up for learning, but suspect you've missed the intent of the OP's post.

I have a feeling (please correct me if I'm wrong again) that the original question was really about where in the zoom range does a 100-400mm lose AF when a TC is attached, presumably because the change in total aperture reported to the camera makes AF impossible.

If at 100mm, the aperture is f/4.5 minus whatever the TC adds - at 400m this aperture will be f/5.6 minus whatever the TC adds, so it is entirely possible that the camera may be able to AF when at 100mm, and not at 400mm. At least I think so.. :-)


some fairly old canon camera stuff, canon lenses, Manfrotto "thingy", 1D MK II converted for IR, and now an M5
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John ­ Sheehy
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Feb 08, 2018 10:11 |  #14

joeseph wrote in post #18559115 (external link)
I'm always up for learning, but suspect you've missed the intent of the OP's post.

I have a feeling (please correct me if I'm wrong again) that the original question was really about where in the zoom range does a 100-400mm lose AF when a TC is attached, presumably because the change in total aperture reported to the camera makes AF impossible.

If at 100mm, the aperture is f/4.5 minus whatever the TC adds - at 400m this aperture will be f/5.6 minus whatever the TC adds, so it is entirely possible that the camera may be able to AF when at 100mm, and not at 400mm. At least I think so.. :-)

It's not a whole stop difference, though, so you don't break into another discrete full-stop category that the camera requires to allow attempt at AF, as might happen at f/4, if that was the open f-number at 100mm. In terms of actual AF performance, though, there is no question that it is possible that the f/4.5 focal length AFes better than the f/5.6 at full zoom, if the optics aren't too highly optimized for 400mm. It would take a TC like a 1.7x )f/7.6-f/9.5 to test if the short end can actually become AF-legal when the long end isn't, and an f/8 camera.

I just tried the lens in very low light and TC'ed to 140-560/6.3-8, and there was less hunting at 140/6.3 than at 560/8.




  
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00derek
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Feb 08, 2018 12:58 as a reply to  @ CyberDyneSystems's post |  #15

I don't own any extenders but I was considering the Canon 2X (II or III) - I had heard tales of it losing AF and wanted some advice. In a previous post on POTN I was told it loses AF at 400mm, but I can see from the discussion here that it's about the aperture not the focal length. A TC may work better at the minimum zoom than maximum, but I'm sure no one bolts on a TC to shoot at 200mm with a 100-400 zoom.

My body is a Canon 5D mk IV.

Sounds like 1.4X III is the one I should be looking into.

Thank you all.




  
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