Lens Extender (Canon, Kenko) - The scoop

I wonder if there is a way to trick the camera into thinking that a 2x TC is actually a 1.4x. For example to use a 2x TC on a 7D with a 500mm f/4 lens and still get AF. My thinking is that is the camera thinks that there is a 1.4x TC engaged that it will slow the focus a bit for better operation but it won’t stop AF altogether.

Greg

no, you would have to interface into the communication between lens and camera.

If you are up for an experiment, you could exchange the chip in the extender with one from a 1.4 extender. You would have to adjust exposure but otherwise it should work.

Not saying this is practical though ...

Exactly, it might be as simple as just covering up the correct pin. Once I get my 2x TC back I am going to try to play around with it. I don’t think you would actually have to change the chip but who knows, maybe you do.

The exposure is done TTL. One thing that you might not be aware of is that when you stack 1.4x and 2x TC’s only the 1.4x shows up and no exposure adjustment needs to be done.

Greg

the way the lens communicates is through a (I believe serial) protocol over some of the 8 main pins. All L lenses that work with the extender have 3 extra pins that communicate with the extender and the extender with the body.

If you tape the pins you interrupt the communication with the lens and the extender and I suspect it goes in some sort of back up emergency mode.

It does not matter how many of those 3 pins you tape, it all leads to the same result, so I suspect it is a serial communication it prevents, rather than "present" / "not present" pins.

Greg Lavaty wrote:

Exactly, it might be as simple as just covering up the correct pin. Once I get my 2x TC back I am going to try to play around with it. I don’t think you would actually have to change the chip but who knows, maybe you do.

The exposure is done TTL. One thing that you might not be aware of is that when you stack 1.4x and 2x TC’s only the 1.4x shows up and no exposure adjustment needs to be done.

Greg

Agreed, the three extra pins tell the lens that the TC is there. However, I think it is just a simple switch, basically, no TC is when no pins are present, 1.4x TC is when some connection is made between them and 2x TC is with a different connection is made. I think you might be able to just cover one pin and trick it but that is just a guess.

It shouldn’t be too tough to figure out. Unfortunately my 2x TC is in HI at the moment with a friend and I won’t have it for a couple of weeks to play with.

Greg

Just for the record, here's how the original and Version II Extenders, and the Life Size Converter for the 50/2.5, report their presence to the lens.

They contain NO electronic logic circuits.

Of the three extra pins, that nearest to the standard pins is "common". In the Extender/LSC it is simply connected to one or both of the two other extra pins. Three combinations are accordingly possible. The LSC has the common extra pin connected to the pin nearer to it. The Extender 2× has the common pin connected to the pin further from it. The Extender 1.4× has the common pin connected to both pins. That's all there is to it. The standard pins are connected straight through to the contact pads on the camera side of the Extender/LSC. The lens uses the open/closed circuit logic to recognise the presence and type of the Extender/LSC, and in efect reports itself to the camera as a different lens.

You will see that this does not provide any way of distinguishing original and Version II Extenders. Since the original and Version II Extender 1.4× are optically identical, that does not matter, but the original and Version II Extender 2× are optically different. I assume, but do not know, that aberration correction in DPP for the Extender 2× is optimised for Version II.

The Version III Extenders do contain some electronics, but my understanding is that for backwards compatibility with Extender-compatible lenses pre-dating their introduction, they also implement the open/closed circuit logic using the three extra pins, and that the electronics is effective only with the new Version II Great White Lenses (and no doubt with future Extender-enabled lenses).

To make an Extender 2× (original or II) appear as an Extender 1.4×, you would need to connect the common pin to the pin immediately next to it.

This is pretty much what I had guessed and when I get my TC back I am going to try it. I don’t know if it would help in trying to make the 2x AF on my 7D with my 500 but if it did that would be pretty nice.

Thanks for posting this.

Greg

This is interesting, but not particularly new. Particularly the thing about taping pins.

certainly not news but I hard a hard time finding all the info I needed

By the way, the reason autofocus is disabled above f5.6 is for reliability. The autofocus system looks as close to the edge of the aperture disc as possible as part of the focus system and the narrowest apeture that this will work at is a design restriction of the autofocus system.

This is true, but since it works just fine on the 7D in bright light and also the focus lights are disabled, it would be the right thing to do to have a custom function to enable it at the users own risk.

Sometimes, autofocus can be achieved because the aperture when wide open is slightly further open than the nominal value set to (ie f5.6 is actually f5.2 - not fast enough to be called f5.0) which which means when the apeture value is reduced by 1 or 2 stops it is still within the tolerance range that the autofocus range can work with. But it might equally be outside of the tolerance range. Unfortunately tolerance is a fact of life and so to avoid "complains" as you say, this has to be designed into the control system.

yes but see above. I like to make those decisions for myself

Don't mistake this for Canon wanting you to have to buy a better camera by disabiling some simple switch in software. If they wanted to do that, your camera would stop working every 11 months to force you to buy a new one!

yes true ... but I am sure it wont hurt them that the folks who want to use the 500 f4 with a 2x converter have to get a 1D

RS_RS wrote:

Just for the record, here's how the original and Version II Extenders, and the Life Size Converter for the 50/2.5, report their presence to the lens.

They contain NO electronic logic circuits.

Of the three extra pins, that nearest to the standard pins is "common". In the Extender/LSC it is simply connected to one or both of the two other extra pins. Three combinations are accordingly possible. The LSC has the common extra pin connected to the pin nearer to it. The Extender 2× has the common pin connected to the pin further from it. The Extender 1.4× has the common pin connected to both pins. That's all there is to it. The standard pins are connected straight through to the contact pads on the camera side of the Extender/LSC. The lens uses the open/closed circuit logic to recognise the presence and type of the Extender/LSC, and in efect reports itself to the camera as a different lens.

I tend to doubt that but if it is the case then one would have to tape the pins on the camera side and not on the lens side as it would be the reason why the AF performs so poorly with taped pins. If you tape the pins on the lens side, the extender would still report an extender is mounted.

Also if it was the case then there is no reason to have 3 extra pins on the lens as the camera would know from the extender, that an extender is mounted

You will see that this does not provide any way of distinguishing original and Version II Extenders. Since the original and Version II Extender 1.4× are optically identical, that does not matter, but the original and Version II Extender 2× are optically different. I assume, but do not know, that aberration correction in DPP for the Extender 2× is optimised for Version II.

The Version III Extenders do contain some electronics, but my understanding is that for backwards compatibility with Extender-compatible lenses pre-dating their introduction, they also implement the open/closed circuit logic using the three extra pins, and that the electronics is effective only with the new Version II Great White Lenses (and no doubt with future Extender-enabled lenses).

it could explain why mine didnt really work... perhaps taping pins works better on version II

To make an Extender 2× (original or II) appear as an Extender 1.4×, you would need to connect the common pin to the pin immediately next to it.

Matt wrote:

RS_RS wrote:

Just for the record, here's how the original and Version II Extenders, and the Life Size Converter for the 50/2.5, report their presence to the lens.

They contain NO electronic logic circuits.

Of the three extra pins, that nearest to the standard pins is "common". In the Extender/LSC it is simply connected to one or both of the two other extra pins. Three combinations are accordingly possible. The LSC has the common extra pin connected to the pin nearer to it. The Extender 2× has the common pin connected to the pin further from it. The Extender 1.4× has the common pin connected to both pins. That's all there is to it. The standard pins are connected straight through to the contact pads on the camera side of the Extender/LSC. The lens uses the open/closed circuit logic to recognise the presence and type of the Extender/LSC, and in efect reports itself to the camera as a different lens.

I tend to doubt that

Believe it, it's a fact.

but if it is the case then one would have to tape the pins on the camera side and not on the lens side as it would be the reason why the AF performs so poorly with taped pins. If you tape the pins on the lens side, the extender would still report an extender is mounted.

You really don't understand, do you? Taping breaks the contact between the extra pins on the Extender and those on the lens. It makes no difference which side you tape, except for which is going to be messier and more likely to cause damage. The reason for poor AF performance with pins taped is (a) when the combined aperture is narrower than f/5.6 the AF system is out of its comfort zone, and (b) AF speed is not adjusted and hunting is likely.

Also if it was the case then there is no reason to have 3 extra pins on the lens as the camera would know from the extender, that an extender is mounted

Again, you don't understand. The camera does not recognise the Extender (original/II), that is done by the lens. All the logic is in the lens, and as far as the camera is concerned the lens+Extender combination is simply a different lens.

You will see that this does not provide any way of distinguishing original and Version II Extenders. Since the original and Version II Extender 1.4× are optically identical, that does not matter, but the original and Version II Extender 2× are optically different. I assume, but do not know, that aberration correction in DPP for the Extender 2× is optimised for Version II.

The Version III Extenders do contain some electronics, but my understanding is that for backwards compatibility with Extender-compatible lenses pre-dating their introduction, they also implement the open/closed circuit logic using the three extra pins, and that the electronics is effective only with the new Version II Great White Lenses (and no doubt with future Extender-enabled lenses).

it could explain why mine didnt really work... perhaps taping pins works better on version II

Perhaps. All my earlier comments refer only to original or Version II Extenders.

To make an Extender 2× (original or II) appear as an Extender 1.4×, you would need to connect the common pin to the pin immediately next to it.

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Of the three extra pins, that nearest to the standard pins is "common". In the Extender/LSC it is simply connected to one or both of the two other extra pins. Three combinations are accordingly possible. The LSC has the common extra pin connected to the pin nearer to it. The Extender 2× has the common pin connected to the pin further from it. The Extender 1.4× has the common pin connected to both pins. That's all there is to it. The standard pins are connected straight through to the contact pads on the camera side of the Extender/LSC. The lens uses the open/closed circuit logic to recognise the presence and type of the Extender/LSC, and in efect reports itself to the camera as a different lens.

I tend to doubt that

Believe it, it's a fact.

but if it is the case then one would have to tape the pins on the camera side and not on the lens side as it would be the reason why the AF performs so poorly with taped pins. If you tape the pins on the lens side, the extender would still report an extender is mounted.

You really don't understand, do you? Taping breaks the contact between the extra pins on the Extender and those on the lens. It makes no difference which side you tape, except for which is going to be messier and more likely to cause damage. The reason for poor AF performance with pins taped is (a) when the combined aperture is narrower than f/5.6 the AF system is out of its comfort zone, and (b) AF speed is not adjusted and hunting is likely.

this was a mistake on my side, the body side only has 8 pins, there is nothing to tape. the extra pins dont connect to the camera.

Also if it was the case then there is no reason to have 3 extra pins on the lens as the camera would know from the extender, that an extender is mounted

Again, you don't understand. The camera does not recognise the Extender (original/II), that is done by the lens. All the logic is in the lens, and as far as the camera is concerned the lens+Extender combination is simply a different lens.

Maybe you would like to shine some of your wisdom on the following points:

the extender on the camera side has the usual 8 EF mount pins which for the most part are 2 data pins, ground and positive. If the extender had no electronic inside and did nothing then how would the camera know that one or the other pin that senses the extender is pulled to ground and to do something different? If it wasnt for electronics in the converter that senses the extender and intercepts the communication between body and lens.

Do you suggest that pulling a pin on the extender to ground will somehow modify the data is exchanged between the body and the lens and modify AF speed, adjust exposure and reports different focal length?

It seems more logical to me that the extender senses an EF lens and then puts itself into the communication between lens and body and makes the body believe a longer lens is attached and also changes the true f stop it gets from the lens.

You will see that this does not provide any way of distinguishing original and Version II Extenders. Since the original and Version II Extender 1.4× are optically identical, that does not matter, but the original and Version II Extender 2× are optically different. I assume, but do not know, that aberration correction in DPP for the Extender 2× is optimised for Version II.

The Version III Extenders do contain some electronics, but my understanding is that for backwards compatibility with Extender-compatible lenses pre-dating their introduction, they also implement the open/closed circuit logic using the three extra pins, and that the electronics is effective only with the new Version II Great White Lenses (and no doubt with future Extender-enabled lenses).

See above, it is not conceivable that any other extender contains no electronic.

it could explain why mine didnt really work... perhaps taping pins works better on version II

Perhaps. All my earlier comments refer only to original or Version II Extenders.

it still makes no sense that there wouldnt be any electronic in it.

To make an Extender 2× (original or II) appear as an Extender 1.4×, you would need to connect the common pin to the pin immediately next to it.

This may be plausible.

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Given that that lens costs far more than any camera Canon makes, I don't suppose they're all that bothered about what camera it is being used on.

hear, hear, that from a company that cripples their cheap bodies so that people buy the next better one?

Matt wrote:

Of the three extra pins, that nearest to the standard pins is "common". In the Extender/LSC it is simply connected to one or both of the two other extra pins. Three combinations are accordingly possible. The LSC has the common extra pin connected to the pin nearer to it. The Extender 2× has the common pin connected to the pin further from it. The Extender 1.4× has the common pin connected to both pins. That's all there is to it. The standard pins are connected straight through to the contact pads on the camera side of the Extender/LSC. The lens uses the open/closed circuit logic to recognise the presence and type of the Extender/LSC, and in efect reports itself to the camera as a different lens.

I tend to doubt that

Believe it, it's a fact.

but if it is the case then one would have to tape the pins on the camera side and not on the lens side as it would be the reason why the AF performs so poorly with taped pins. If you tape the pins on the lens side, the extender would still report an extender is mounted.

You really don't understand, do you? Taping breaks the contact between the extra pins on the Extender and those on the lens. It makes no difference which side you tape, except for which is going to be messier and more likely to cause damage. The reason for poor AF performance with pins taped is (a) when the combined aperture is narrower than f/5.6 the AF system is out of its comfort zone, and (b) AF speed is not adjusted and hunting is likely.

this was a mistake on my side, the body side only has 8 pins, there is nothing to tape. the extra pins dont connect to the camera.

Good. We make progress.

Also if it was the case then there is no reason to have 3 extra pins on the lens as the camera would know from the extender, that an extender is mounted

Again, you don't understand. The camera does not recognise the Extender (original/II), that is done by the lens. All the logic is in the lens, and as far as the camera is concerned the lens+Extender combination is simply a different lens.

Maybe you would like to shine some of your wisdom on the following points:

the extender on the camera side has the usual 8 EF mount pins which for the most part are 2 data pins, ground and positive. If the extender had no electronic inside and did nothing then how would the camera know that one or the other pin that senses the extender is pulled to ground and to do something different? If it wasnt for electronics in the converter that senses the extender and intercepts the communication between body and lens.

Do you suggest that pulling a pin on the extender to ground will somehow modify the data is exchanged between the body and the lens and modify AF speed, adjust exposure and reports different focal length?

You STILL haven't got your mind round it. The lens contains the electronics. THE EXTENDER (original, II) ONTAINS NO ELECTRONICS. The (Extender-enabled) lens tests what the common extra contact pad on its rear end is connected to. If it is not connected to either of the other extra contact pads, it assumes no Extender is present. If there is a connection, that tells it that an Extender is present and if so what kind. All that the Extender has to do is to provide the connection. Once the lens has established whether an Extender is present, and if so what type, it reports back to the camera, and slows its AF operation, in the appropriate way. What's hard to understand about this?

It seems more logical to me that the extender senses an EF lens and then puts itself into the communication between lens and body and makes the body believe a longer lens is attached and also changes the true f stop it gets from the lens.

You could do it like that, and I believe some off-brand TCs do so, and it may be that the Version III Extenders use their internal electronics to do this, at least with the Version II Great White Lenses. But the fact is that this is NOT how the original and Version II Extenders (and the Life Size Converter) actually work.

You will see that this does not provide any way of distinguishing original and Version II Extenders. Since the original and Version II Extender 1.4× are optically identical, that does not matter, but the original and Version II Extender 2× are optically different. I assume, but do not know, that aberration correction in DPP for the Extender 2× is optimised for Version II.

The Version III Extenders do contain some electronics, but my understanding is that for backwards compatibility with Extender-compatible lenses pre-dating their introduction, they also implement the open/closed circuit logic using the three extra pins, and that the electronics is effective only with the new Version II Great White Lenses (and no doubt with future Extender-enabled lenses).

See above, it is not conceivable that any other extender contains no electronic.

it could explain why mine didnt really work... perhaps taping pins works better on version II

Perhaps. All my earlier comments refer only to original or Version II Extenders.

it still makes no sense that there wouldnt be any electronic in it.

To make an Extender 2× (original or II) appear as an Extender 1.4×, you would need to connect the common pin to the pin immediately next to it.

This may be plausible.

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