Teleconverters and the number of electrical contacts on the lens?

My apologies to if this was put somewhere else I could not find it in either TC thread above. Well I didn’t go through all 40+ pages of the one thread, because it was mostly on AF – not what I was caring about.

My apologies to the moderators, especially CyberDyneSystems, if this should have posted there. But I wanted answers, and more people look and respond here than they do there! Please move to the correct place – if needed. If I can ask, please wait a day or so until an answers can be given.

I don’t think TCs register on any Canon lens that is not designated to work one of Canon’s TCs. My Kenkos (1.4X & 2X) both register with my 70-200L, 135L, and my Sigma 150-500. I don’t know about the Sigma but those two Canon lenses are designed to take the Canon TCs. None of my other lenses register (Canon or otherwise) their presence with the TCs except my 50mm CM. I think that is because it is designed to take the Life Size Converter which is partially a TC but also with some extension. (Same effect but with a multiple of 2 with the 2X)

(With my versions which are Kenko Pro 300s one original and one DG) What I’ve figured out is if the Canon lens (this was not true for one of my three Sigma lenses) has 8 contacts after the “fat/big” contact (so 10 total contacts), then it will register. If it has only 5 contacts (7 total), then it will not register correctly. So with a 1.4X my 135L shows in the EXIF as a 189mm f/2.8.! While with the 1.4x my 100mm macro shows as a 100mm macro at f/2.8, but really it is acting as a 140mm macro at f/4!

I do not know for sure, but I would assume it works this way for all brands of TCs. That is assuming the information is going through those last 3 contacts.

I’m not caring about AF here, just correct aperture and FL representation. I’ll assume the f/5.6 limitation (unless a 1D model then f/8) for AF. What I want to know is the data reporting. I’m thinking it is not a limitation of the TCs, but of the lenses themselves.

Does anyone know if what I’ve figured is correct?

Does anyone have a TC brand (Tamron, Sigma, Kenko DGX, etc…) that correctly represents the “modified” FL and aperture changes for a lens with only the 5 contacts (7total) like a 50mm (any but the f/2.5), an 85mm (basically any Canon brand lenses not on the Canon TC compatibility chart and the CM)? [If you have one, please post the combination].

Or would be willing to try with their lens and TC?

Thanks in advance!

jimewall wrote in post #14717358
Does anyone have a TC brand (Tamron, Sigma, Kenko DGX, etc…) that correctly represents the “modified” FL and aperture changes for a lens with only the 5 contacts (7total) like a 50mm (any but the f/2.5), an 85mm (basically any Canon brand lenses not on the Canon TC compatibility chart and the CM)? [If you have one, please post the combination]

What you've stated is basically correct (the lens - as well as the TC - need those extra contacts). The answer to the above question, and the exception, is the Kenko DGX TCs (or at least the Kenko Pro 300 DGX) - if the extra contacts are not present then it appears to intercept the comms and modify the focal-length and aperture fields itself.

In other words, if you put a Kenko Pro 300 DGX 1.4x behind a Canon 85 F/1.8 then the correctly modified focal-length and f-stop are shown on the camera and reported in the EXIF data.

phreeky wrote in post #14717450
What you've stated is basically correct (the lens - as well as the TC - need those extra contacts). The answer to the above question, and the exception, is the Kenko DGX TCs (or at least the Kenko Pro 300 DGX) - if the extra contacts are not present then it appears to intercept the comms and modify the focal-length and aperture fields itself.

In other words, if you put a Kenko Pro 300 DGX 1.4x behind a Canon 85 F/1.8 then the correctly modified focal-length and f-stop are shown on the camera and reported in the EXIF data.

Thank you! It looks like I will need to upgrade my Kenko.

So then is my my conclusion that it is not the teleconverter's limitation but the len's limitation correct? It is just Kenko (maybe others) has/have found a way to somehow bypass the limitation?

Yes it's a lens limitation. Traditionally the TC doesn't talk to the camera - it reports its presence to the lens via the extra pins and the other pins are simply pass-through. The Kenko DGX TCs actually modify the data reported. In addition, the DGX TCs use the same trick as some Sigma/Tamron zooms (those that are F/6.3 at the long end) and allows combinations > F/5.6 to still AF, despite reporting the correct aperture to the camera.

phreeky wrote in post #14718066
Yes it's a lens limitation. Traditionally the TC doesn't talk to the camera - it reports its presence to the lens via the extra pins and the other pins are simply pass-through. The Kenko DGX TCs actually modify the data reported. In addition, the DGX TCs use the same trick as some Sigma/Tamron zooms (those that are F/6.3 at the long end) and allows combinations > F/5.6 to still AF, despite reporting the correct aperture to the camera.

I have one of those Sigmas (150-500). Do you know if this would keep AF if I attach a DGX to my Sigma (without the tape trick)? Not that that really matters to me, I still will only occasional use it, and still plan on upgrading my TC.

I don't know about the 150-500 specifically, but it attempts AF on F/5.6 lenses so I see no reason why it wont work. I'd be surprised if the AF is very useful at such a small aperture though (it will perform the same as using the tape trick on your DG version).

I see no reason to change your converter. OK, so the EXIF is wrong, so what?

I have purposely taped over the pins that do the reporting for reasons that don't concern us here. It makes absolutely no difference to the way the camera/lens performs except in one crucial area and which is the reason I taped them. Everything else is unchanged.

phreeky wrote in post #14718768
I don't know about the 150-500 specifically, but it attempts AF on F/5.6 lenses so I see no reason why it wont work. I'd be surprised if the AF is very useful at such a small aperture though (it will perform the same as using the tape trick on your DG version).

It does work with the tape trick. Reasonably with the 1.4X! In very good light with the 2X, it is very iffy!

I prefer not to use the tricks, so the hope would be for the DGX not to need them.

Lowner wrote in post #14718787
I see no reason to change your converter. OK, so the EXIF is wrong, so what?

I have purposely taped over the pins that do the reporting for reasons that don't concern us here. It makes absolutely no difference to the way the camera/lens performs except in one crucial area and which is the reason I taped them. Everything else is unchanged.

Though I partially agree, but (as I said above) I'd rather not tape the pins if I did not have to.