topic Re: 2 x extender autofocus in EOS DSLR & Mirrorless Cameras

2 x extender autofocus

BryanShaw1 — Wed, 02 Jun 2021 12:00:04 GMT

I have just purchased a used Canon 2 x extender II.

When fitted to my 7D, the Q screen automatically changes to MF MANUAL FOCUS.

Is the extender faulty?

Re: 2 x extender autofocus

Waddizzle — Wed, 02 Jun 2021 12:35:08 GMT

No, it is not faulty. The 2x extenders do not work with, or allow for autofocus, with any and all combinations of cameras and lenses.

Re: 2 x extender autofocus

kvbarkley — Wed, 02 Jun 2021 13:15:38 GMT

More importantly, which lens do you have?

Re: 2 x extender autofocus

wq9nsc — Wed, 02 Jun 2021 13:46:38 GMT

The 7D AF system won't work if the combined lens plus 2X aperture is above f5.6. So unless you are using a f2.8 or faster lens, the 2X will put your 7D out of AF range. A lens with a maximum aperture of f4 combined with a 1.4X will autofocus with your 7D because the one stop loss from the 1.4X results in a f5.6 combo. The same f4 plus 2X results in a 2 stop loss of aperture putting the 7D out of its AF capable range.

Even with the sharpest primes I own (EF 200 f2, EF 300 and 400 f2.8), results with the 2X converter are most underwhelming. With the sharp primes, the image looks OK until you compare and see how much IQ degradation occurs compared to the bare lens. With lesser glass, the results will be even less impressive.

The 1.4X does work quite well with many lenses and as long as the bare lens is f4 or faster, it will AF with your 7D.

The 1 series will AF with aperture combinations as slow as f8 but even with my 1DX III the AF is noticeably slower and less sure with this combination (i.e. using an EF 800 f5.6 with the 1.4X which results in f8 combined and it will AF but nothing like the lightning quick results with the bare lens).

Rodger

Re: 2 x extender autofocus

BryanShaw1 — Wed, 02 Jun 2021 14:03:37 GMT

The lens is the EF 100-400 L IS.

Without the extender the autofocus options in the Q menu are all operational. When the extender is fitted it only shows a green box MF. Pressing the set button twice turns the box blue but still shows MF. (I'm trying to give as much info here as possible)

I know that AF is hit and miss with extenders but It's as if it's somehow switched off - there is nothing there at all, whatever the apperture.

Re: 2 x extender autofocus

ebiggs1 — Wed, 02 Jun 2021 14:42:57 GMT

"The lens is the EF 100-400 L IS."

The 2x tel-con is not compatible with that lens. AF is possible only with a lens that has an f2.8 or faster maximum aperture. Your lens is a f5.6.

Re: 2 x extender autofocus

wq9nsc — Wed, 02 Jun 2021 14:37:50 GMT

With the 2X extender in place, even a 1DX III will not AF with using the normal AF system with that particular lens. With your 7D, AF won't work with the 1.4X either because the aperture rises beyond the f5.6 capability of the 7D as soon as you add an extender. Once your 100-400 is zoomed out to the f5.6 region, it is at the aperture limit of the 7D.

Your 7D turns off the AF function when you add the extender because the camera knows that its AF system won't work with that lens/extender combination.

I have never used live view with a 7D so I don't know what AF capabilities it has in live view. It MIGHT work in live view with that combination but it will work very slowly.

Rodger

Re: 2 x extender autofocus

BryanShaw1 — Wed, 02 Jun 2021 14:47:57 GMT

would the combination work with a EOS R?

Re: 2 x extender autofocus

ebiggs1 — Wed, 02 Jun 2021 14:52:36 GMT

It will not even mount with out an adapter.

Re: 2 x extender autofocus

ebiggs1 — Wed, 02 Jun 2021 14:55:31 GMT

The bottom line is it is not a good idea with such a slow lens. Plus a lens that doesn't have the IQ, in the first place, to give up to the tel-con even if you could get it to work.

Re: 2 x extender autofocus

jrhoffman75 — Wed, 02 Jun 2021 17:12:26 GMT

To be precise, the Canon 2X extender is compatible with the 100-400 zoom, but autofocus will not work.

Re: 2 x extender autofocus

Waddizzle — Thu, 03 Jun 2021 05:00:50 GMT

@BryanShaw1 wrote:
would the combination work with a EOS R?

It might, but just not very well. Mirrorless cameras behave similar to Live View would in a DSLR.

Let''s take a step back to your 7D for a moment, though. The 7D User Guide should include a section about "Lens Groups", which is where the information is located where I based my previoious comments regarding camera/lens compatibility.

When you add an extender, this reduces the amount of light reaching the image sensor, and more importantly the amount of light that is reaching the AF sensor assembly. The User Guide explains and describes AF points in terms of their sensitivity to various aperture settings, which is way of describing the minimum amount ot light needed for an AF point to function most accurately.

When you add the 2x teleconverter to slower lenses, you will be significantly reducing the amount of light that will be reaching the AF sensor assembly. Can the AF sensor assembly function with reduced light? At a guess, I would think it that it could, but it just won't anywhere near as accurate as without it.

And so, the camera's firmware disables the automatic AF system when the maximum lens aperture reduces to a certain level. But, if you switch the lens to MF, and use One Shot AF mode in the camera, don't be surprised if the camera does not beep an AF lock as you try to manually focus something as you hold the shutter half pressed. I have focused on the Moon with my T5 many times this way as I focused in Live View.

So, what would happen with a mirrorless camera like the EOS R? You should expect a reduction in the number of available AF points, just as what would happen with a DSLR.

Canon has released 600mm and 800mm lenses with fixed f/11 apertures. What they don't tell you is that the cameras will only have active AF points in the center area of the viewfinder, giving you AF point coverage in the EVF similar to what you might have in a DSLR OVF. I suspect this reduction in "edge to edge" AF point coverage could be due to vignetting in the lenses around the edges of the frame, which naturally means reduced amounts of light reaching the AF system.

Re: 2 x extender autofocus

BryanShaw1 — Thu, 03 Jun 2021 08:27:32 GMT

Grateful for that comprehensive reply.

A couple of points:

When I switch the lens to manual focus, the camera still remains at 'MF' in the Q menu.

Years ago I bought a cheap 2 x from Jessops so I thought I'd try it. Interestingly, the camera now allows autofocus settings.

Re: 2 x extender autofocus

jrhoffman75 — Thu, 03 Jun 2021 10:08:05 GMT

@BryanShaw1 wrote:
Grateful for that comprehensive reply.
A couple of points:
When I switch the lens to manual focus, the camera still remains at 'MF' in the Q menu.

Years ago I bought a cheap 2 x from Jessops so I thought I'd try it. Interestingly, the camera now allows autofocus settings.

Yes, some third party tele-extenders do not report back the "adjusted" f/stop, so the camera does not disable AF.

But, the reason Canon disables the AF feature beyond either f/5.6 or f/8 (depending on the camera) is that the reduced light can really slow down the AF speed/capability. Canon wants to maintain the user experience.

Re: 2 x extender autofocus

kvbarkley — Thu, 03 Jun 2021 13:06:47 GMT

"It might, but just not very well. Mirrorless cameras behave similar to Live View would in a DSLR."

Actually, it works much better. The R's have phase detection sites on the sensor which work much better than the contrast detection that DSLR's normally use.

That is why the RF 800 and 600 mm F/11 lenses can autofocus.

Ken Rockwell hooked up an EOS R to an EF100-400, a 1.4X teleconvertor, a 2 X teleconverter and an EOS to RF adapter to his R and it autofocused fine.

https://www.kenrockwell.com/canon/eos-r/r.htm

Re: 2 x extender autofocus

BryanShaw1 — Thu, 03 Jun 2021 13:49:14 GMT

Wow, that changes things! - It was just about to go on ebay.

Re: 2 x extender autofocus

jrhoffman75 — Thu, 03 Jun 2021 18:09:09 GMT

I had to hang around the house waiting for a service tech, so I decided to run a little test.

I set up my 1D X Mark III on a tripod and mounted a test image on the garage door.

With the EF100-400 f/4-5.6L II mounted with the 2X VIII telextender I framed the shot, trying to pretty much fill the frame.

Then I mounted the 1.4x and finally no extender (1X).

In Canon DPP I turned off all sharpening and performed the Digital Lens Optimizer process.

Once that completed I switched to the Fine Detail Picture Style.

Once completed I cropped the 1.4X and 1X images to match the 2X as close as I could. Then I exported them as 16bit TIFF files. File sizes were 114MB, 54MB and 27MB (2X, 1.4X and 1X).

Then I did a Windows screen capture which produced JPEGs.

1.4X

I'm curious what you folks think. From my observation and this limited test my thoughts are 1. the 2X image doesn't seem bad and 2. if one doesn't have a telextender cropping the basic lens, even with just a 20MP body, gives pretty good results.

For reference, here is the full 1X image and a 100 percent zoom.

Re: 2 x extender autofocus

Waddizzle — Thu, 03 Jun 2021 21:04:04 GMT

@kvbarkley wrote:
"It might, but just not very well. Mirrorless cameras behave similar to Live View would in a DSLR."

Actually, it works much better. The R's have phase detection sites on the sensor which work much better than the contrast detection that DSLR's normally use.

That is why the RF 800 and 600 mm F/11 lenses can autofocus.

Ken Rockwell hooked up an EOS R to an EF100-400, a 1.4X teleconvertor, a 2 X teleconverter and an EOS to RF adapter to his R and it autofocused fine.
https://www.kenrockwell.com/canon/eos-r/r.htm

Dual Pixel AF uses phase detection. It always has.

https://www.usa.canon.com/internet/portal/us/home/learn/education/topics/article/2018/July/Intro-to-Dual-Pixel-Autofocus-(DPAF)/Intro-to-Dual-Pixel-Autofocus-(DPAF)

Re: 2 x extender autofocus

CaliforniaDream — Thu, 03 Jun 2021 23:00:16 GMT

I have an R5 and with my 600mm F11 with a 2X extender and good light it auto focuses quite well and very fast. That same combination except with my 100-500 and 2x snaps into focus fast enough to capture BIF's. Amaizing camera and lens.

Re: 2 x extender autofocus

CaliforniaDream — Thu, 03 Jun 2021 23:12:53 GMT

This use to be true, But not anymore! BTW no flame intended.

@Waddizzle wrote:
No, it is not faulty. The 2x extenders do not work with, or allow for autofocus, with any and all combinations of cameras and lenses.