F00 conundrum

[neuroanatomist]

A camera body will show F00 and manual focus (MF) when it cannot communicate with a lens, which could be because there is no lens attached, because the lens is fully manual, or because there's a problem with the lens itself.

I went out birding over the weekend, mounted my usual combination of 600/4 II, 1.4xIII and the vanilla EF-EOS R Mount Adapter to my R1 and headed out. When I turned on the camera, it showed F00 and MF. I thought, "Oh, sh!t," and swapped on the 2xIII. That worked...but then it also changed to F00 and MF. So I mounted just the bare lens...and that was perfectly fine so I spent the day shooting like that.

When I got home, I cleaned all the contacts and tested various combinations again, including changing out the vanilla mount adapter for the drop-in version and my 3rd party adapter modified for an RF extender to fit behind it.

The upshot was this, and the situation is seemingly stable (through many trials over a couple of days, no changes). Happens on both the R1 and the R8, and with all three of the mount adapters.

• Bare 600/4 II – functions normally
• 600/4 II + 1.4xIII – F00 and MF
• 600/4 II + 2xIII – varies between:
  • Normal function
  • Showing an aperture value that can be adjusted, but still only MF
  • F00 and MF
  • The variation is caused by physical manipulation – twisting the lens in the mount or moving the lens, e.g., lifting it from pointing down into shooting position, affects the functionality
• 600/4 II + RF 1.4x (with Commlite adapter) – functions normally

The fact that I see this behavior with two bodies and three adapters suggests the problem is the TCs or the lens.

I haven't used the 2xIII TC quite some time, not since Comet C:2023 A3 Tsuchinshan-ATLAS in October 2024. So maybe the 2xIII failed sometime over the past 18 months (while sitting mostly undisturbed in a Pelican case with a dehumidifier unit), and the 1.4xIII failed sometime in the past 3.5 weeks since I last used it.

If it's the lens and not the TCs, the problem is specific to use with EF TCs and yet the problem exhibits different symptoms with the two TCs, and I don't know why that would be the case. Admittedly, I would prefer it to not be the lens, because the service life for the 600/4 II ended last year, so sending it to Canon is not an option. I could replace it with the RF 600/4, but I suspect we'll see a version of that lens with the 1.4x TC and hopefully fairly soon. I would love to have the latter and would not love buying twice.

One other idea occurred to me, literally as I was typing this post. I started to write that I don't have any other TC-compatible EF lenses with which to test the extenders...and realized that while that is true, I do have three other EF mount lenses that are physically compatible with the extenders, but don't report them to the camera body (TS-E 17, TS-E 24 and MP-E 65). So I tried the 1.4xIII and the 2xIII with the TS-E 24, and I found that the 1.4xIII shows F00, and the 2xIII shows an aperture value that can be adjusted.

It seems rather unlikely that both TCs independently failed, but I am thinking that's exactly what has happened. Sort of a Sherlock Holmes, "When you have eliminated the impossible, whatever remains, however improbable, must be the truth," sort of thing.

From a practical standpoint, assuming that I'm correct and both extenders have failed, I see no need to replace the 2xIII. One option would be to replace the 1.4xIII ($480 new or $280 used), but I can also just use the RF 1.4x behind my modified Commlite mount adapter, and just remember that I'm doing that since it's not reported in the EXIF. The downside to the latter is that I would not benefit from the DxO lens profile for the combo (though I could batch edit the EXIF and I suspect that DxO would use the 600 II + EF 1.4xIII profile, it still won't be the right profile).

Thoughts, suggestions, and sharing prior experience welcome!

Edit: the RF 1.4x itself does show up in the EXIF, but the exposure information doesn't reflect it, remaining 600mm f/4.

 

[P-visie]

My R5 Mk II + EF 600mm + 1.4 III extender works as advertized (). I hope it is not the lens. Can you borrow (or rent) another EF 1.4 TC to verify that it is not the lens?

 

[neuroanatomist]

Good idea, thanks. Renting would be <$50, I might be able to borrow a copy.

 

[m4ndr4ke]

I would prefer it to not be the lens, because the service life for the 600/4 II ended last year, so sending it to Canon is not an option.

I could be wrong, but it is my understanding that Canon will repair lenses beyond that date, for as long as the necessary parts are still available — they just can’t get new parts, so when they run out of stock it’s really over.

Now, for the issue you’re reporting, firstly I was thinking about the two extra pins for teleconverters, on the lens but, since you were able to try a different lens, it got a little confusing.

My first suggestion would be cleaning all mounts contacts (yes, again) thoroughly, because if there were any kind of grease or dirt that could be creating conductivity issues, you would have pretty much spread it across all lenses, with all the lens swaps you just made while troubleshooting this (contamination). Include the adapters.

Do not use WD40 or any other greasy products, use a dedicated contact cleaner or isopropyl alcohol.

Also check for loose lens mounts bayonets. Include the adapters.

If it doesn’t work, do you have any nearby store where someone knows you? Perhaps you could ask to briefly test a different teleconverter and/or a different lens.

 

[becceric]

My R5, RF to EF adapter, EF 1.4x TC, and EF 600mm f/4 L IS III have had no issues together, but I had that intermittent problem with the same camera, adapter, EF 100mm f/2.8 L IS macro, and a 25mm extension tube.

Cleaning did not correct it, but there was a small bit of flex with all of those connections that revealed itself occasionally.
I replaced the third party extension tube with a Canon one and the problem disappeared.

I noticed the equipment details on your recent nuthatch portrait and thought you had secretly acquired the RF 600 f/4L and was testing it out. Since it now appears that info has been revised, I guess a head to head comparison with your 600mm EF Mark II won't be forthcoming.

I hope you solve the issue and update us as to the cause.

 

[P-visie]

You stated (or I interpreted it that way) in another thread that the problem was solved by cleaning the contacts. Is that correct?

 

[neuroanatomist]

You stated (or I interpreted it that way) in another thread that the problem was solved by cleaning the contacts. Is that correct?

Nope, I believe I stated that it didn’t solve my problem (or at least, that’s what I meant to state). That was before I deleted all of that, subsequent to your post identifying the real problem of the camera in that thread being a 6D.

 

[Raptors]

A camera body will show F00 and manual focus (MF) when it cannot communicate with a lens, which could be because there is no lens attached, because the lens is fully manual, or because there's a problem with the lens itself.

I went out birding over the weekend, mounted my usual combination of 600/4 II, 1.4xIII and the vanilla EF-EOS R Mount Adapter to my R1 and headed out. When I turned on the camera, it showed F00 and MF. I thought, "Oh, sh!t," and swapped on the 2xIII. That worked...but then it also changed to F00 and MF. So I mounted just the bare lens...and that was perfectly fine so I spent the day shooting like that.

When I got home, I cleaned all the contacts and tested various combinations again, including changing out the vanilla mount adapter for the drop-in version and my 3rd party adapter modified for an RF extender to fit behind it.

The upshot was this, and the situation is seemingly stable (through many trials over a couple of days, no changes). Happens on both the R1 and the R8, and with all three of the mount adapters.

• Bare 600/4 II – functions normally
• 600/4 II + 1.4xIII – F00 and MF
• 600/4 II + 2xIII – varies between:
  • Normal function
  • Showing an aperture value that can be adjusted, but still only MF
  • F00 and MF
  • The variation is caused by physical manipulation – twisting the lens in the mount or moving the lens, e.g., lifting it from pointing down into shooting position, affects the functionality
• 600/4 II + RF 1.4x (with Commlite adapter) – functions normally

The fact that I see this behavior with two bodies and three adapters suggests the problem is the TCs or the lens.

I haven't used the 2xIII TC quite some time, not since Comet C:2023 A3 Tsuchinshan-ATLAS in October 2024. So maybe the 2xIII failed sometime over the past 18 months (while sitting mostly undisturbed in a Pelican case with a dehumidifier unit), and the 1.4xIII failed sometime in the past 3.5 weeks since I last used it.

If it's the lens and not the TCs, the problem is specific to use with EF TCs and yet the problem exhibits different symptoms with the two TCs, and I don't know why that would be the case. Admittedly, I would prefer it to not be the lens, because the service life for the 600/4 II ended last year, so sending it to Canon is not an option. I could replace it with the RF 600/4, but I suspect we'll see a version of that lens with the 1.4x TC and hopefully fairly soon. I would love to have the latter and would not love buying twice.

One other idea occurred to me, literally as I was typing this post. I started to write that I don't have any other TC-compatible EF lenses with which to test the extenders...and realized that while that is true, I do have three other EF mount lenses that are physically compatible with the extenders, but don't report them to the camera body (TS-E 17, TS-E 24 and MP-E 65). So I tried the 1.4xIII and the 2xIII with the TS-E 24, and I found that the 1.4xIII shows F00, and the 2xIII shows an aperture value that can be adjusted.

It seems rather unlikely that both TCs independently failed, but I am thinking that's exactly what has happened. Sort of a Sherlock Holmes, "When you have eliminated the impossible, whatever remains, however improbable, must be the truth," sort of thing.

From a practical standpoint, assuming that I'm correct and both extenders have failed, I see no need to replace the 2xIII. One option would be to replace the 1.4xIII ($480 new or $280 used), but I can also just use the RF 1.4x behind my modified Commlite mount adapter, and just remember that I'm doing that since it's not reported in the EXIF. The downside to the latter is that I would not benefit from the DxO lens profile for the combo (though I could batch edit the EXIF and I suspect that DxO would use the 600 II + EF 1.4xIII profile, it still won't be the right profile).

Thoughts, suggestions, and sharing prior experience welcome!

Edit: the RF 1.4x itself does show up in the EXIF, but the exposure information doesn't reflect it, remaining 600mm f/4.
View attachment 228668

I do not own a 600mm lens but recently traveled to South Africa in July 2025 and used the RF 100-300mm 2.8 (CPS trial run) lens. I mounted it with the RF 1.4x on my R1 and the RF 70-200mm 2.8 Z on my R52.

On the second day of shooting, I started experiencing multiple errors, including Err60, Err70, Err 80, and FOO. The R1 would give me an error, shut down, and wouldn’t turn back on. Of course, this happened during a cheetah kill! I swapped cameras to the R52, hoping the contacts on the R1 needed cleaning.

I returned to camp, cleaned the contacts on the R1 and 1.4x, and went out the next day. Unfortunately, the same errors occurred. This time, I also swapped cameras, but this time, I also got errors on the R52.

I contacted Canon South Africa, but since they couldn’t see the lens, they couldn’t really help me. However, they did mention that a new firmware was coming next week that might potentially fix the problem.

Interestingly, when I mounted just the bare lens (100-300 2.8), no errors occurred on either the R1 or R52.

When I returned to Canada, I sent my R1, R52, 1.4x, and their 100-300mm 2.8 to Canon Canada. Their findings were that, since they couldn’t replicate the errors I was getting, it had to be the 1.4x.

The fact that I have no problems with the 1.4x, I still believe the problem was with the 100-300mm 2.8. As I don’t own this lens, I cannot do any further testing.

Hope you get this sorted out!

 

[Nemorino]

Have You tested the lens with TC on a DSLR? Might be a software problem EF/RF as the RF TC works without problems. And it is unlikely both EF-TC fail at the same time.