topic Re: Autofocus problem 6D and 100-400 in EOS DSLR & Mirrorless Cameras

Autofocus problem EOS 6D Mark II and EF 100-400mm

tgo2002 — Sat, 18 Nov 2023 14:31:09 GMT

I have recently-purchased 6D Mark II camera and EF 100-400mm 1:4.5-5.6 L IS II lens. The past few days the lens will not autofocus at 400mm some of the time. If I zoom out to 250mm, focus, then zoom back to 400mm, it will focus. I can re-create the problem easily on the 6D, but on my older 5D Mark III the lens works perfectly.

Has anyone else experienced this? Is it a problem with the camera or the lens?

Re: Autofocus problem 6D and 100-400

Waddizzle — Fri, 17 Nov 2023 23:19:16 GMT

Check the focus limiter switch on the lens!

Make sure you are not too close to subjects!

Re: Autofocus problem 6D and 100-400

jrhoffman75 — Fri, 17 Nov 2023 23:24:40 GMT

If it works on one camera but not the other I would probably rule out the lens.

Be sure that the subject has sufficient contrast. The 5D Mark IV does have a greater number of AF points, so that could be relevant.

Re: Autofocus problem 6D and 100-400

tgo2002 — Fri, 17 Nov 2023 23:27:40 GMT

I'm pointing it at a mountain and it only happens on the 6D, not the 5D. So that is not the problem.

Re: Autofocus problem 6D and 100-400

deebatman316 — Fri, 17 Nov 2023 23:52:04 GMT

The 5D Mark III can also AF at F/8 which the original 6D can not. I would also check the setting called "lens drive when AF Impossible". It should be set to "Continue Focus Search". Also if filters are attached remove them. The EF 100-400mm F/4-5.6L IS USM lens lineup doesn't AF with them well. They cause problems like this all the time.

Re: Autofocus problem 6D and 100-400

jrhoffman75 — Fri, 17 Nov 2023 23:58:18 GMT

Valid points, but I wouldn’t expect them to be camera dependent , considering that there is no mention of a teleconverter.

Re: Autofocus problem 6D and 100-400

deebatman316 — Sat, 18 Nov 2023 00:06:47 GMT

Now I really wasn't focusing on teleconverters or AF at F/8. But I was focusing the "lens drive when AF Impossible" setting. The 5D Mark III & IV use the same 61 point AF system. It kinda sounds like a communication problem though with the 6D.

Edit: The OP mentions BOTH the original 6D and 6D Mark II. So is the problem with both cameras?

Re: Autofocus problem 6D and 100-400

jrhoffman75 — Sat, 18 Nov 2023 00:12:30 GMT

The AF Drive setting is a good item to check. The longer zoom can enlarge the subject and make it harder to get contrast. But, since the OP says he is trying to photograph mountains that may reduce that possibility.

Re: Autofocus problem 6D and 100-400

deebatman316 — Sat, 18 Nov 2023 00:14:18 GMT

Focus limiter switch as @Waddizzle (Bill) brought up? That could be it too.

Re: Autofocus problem 6D and 100-400

jrhoffman75 — Sat, 18 Nov 2023 00:15:14 GMT

OP says mountains.

Re: Autofocus problem 6D and 100-400

tgo2002 — Sat, 18 Nov 2023 00:17:23 GMT

No filters, no teleconverter/extender. The max aperture on the lens is 5.6. I thought maybe low light would make a difference, but it happened today in daylight.

Re: Autofocus problem 6D and 100-400

tgo2002 — Sat, 18 Nov 2023 00:18:52 GMT

Sorry I didn't spell out 6D Mark II both times. I have that and the 5D Mark III.

Re: Autofocus problem 6D and 100-400

deebatman316 — Sat, 18 Nov 2023 00:23:11 GMT

What about the subject's contrast. Your camera relies on CONTRAST to work NOT how bright it is. No first party Canon EF or EF-S lens has EVER had an aperture SMALLER than F/5.6 early lenses had wider open apertures. They were not smaller than F/4.5 but once they figured out that an aperture of F/5.6 provided enough light and contrast to the AF system. That allowed them to make cheaper and smaller lenses.

Re: Autofocus problem 6D and 100-400

deebatman316 — Sat, 18 Nov 2023 00:25:07 GMT

Both of those cameras CAN focus at F/8. I would check the setting called "Lens Drive When AF Impossible". To see if the camera will keep searching for focus instead of stopping.

Re: Autofocus problem 6D and 100-400

tgo2002 — Sat, 18 Nov 2023 00:30:55 GMT

"Lens drive when AF impossible" was set to "Stop." I switched to "Continue" and it seems to be working inside tonight. I will try it in daylight tomorrow before declaring victory, but that might have taken care of it.

For what it is worth, the 5D was set on "Continue."

Re: Autofocus problem 6D and 100-400

deebatman316 — Sat, 18 Nov 2023 00:44:15 GMT

Older Telephoto and Super Telephoto lenses would often get lost and hunt if the camera couldn't lock focus. I had that problem when borrowing my friend's dad original EF 300mm F/2.8L USM (released in 1987) lens while using it on my old EOS 40D. That was Canon's first lens to feature a Ring Type USM AF. It also utilized focus by wire. This was before Canon had designed a clutch override system found in newer Ring Type USM lenses.

Re: Autofocus problem 6D and 100-400

jrhoffman75 — Sat, 18 Nov 2023 03:40:15 GMT

@tgo2002 wrote:
"Lens drive when AF impossible" was set to "Stop." I switched to "Continue" and it seems to be working inside tonight. I will try it in daylight tomorrow before declaring victory, but that might have taken care of it.
For what it is worth, the 5D was set on "Continue."

Whenever there are two devices that should function the same but don't it is important to look for differences. You found one. Are the AF modes the same? Typically a mountain range is an easy subject for One Shot AF with single center point. Good contrast between the mountain and the sky.