A TC20E becomes an electrified extension tube

Started Sep 26, 2012 | Discussions
mmalkin15 Regular Member • Posts: 290
A TC20E becomes an electrified extension tube
1

A TC20E becomes an electrified extension tube

Many of us have been waiting years for Nikon to build a quality electrified extension tube. These are useful for macro work and small live subjects ( dragonflies, butterflies, frogs, etc) where one would like to use some of Nikon’s lenses at closer distances than they can focus. Kenko does make a decent set of such extension tubes and I do use these for some macro work but structurally they are inferior, made of plastic, and just not up to being a solid support for larger lenses like the telephotos and 70-200 or larger size zooms.

Several years ago I did modify a Nikon PN11 by adding contact assemblies to electrify it and although the result is wonderful it was a difficult and very time consuming process to make all the modifications to the PN11 and incorporate the contact assemblies from a scrapped Kenko tube. And - one mistake and it is toast… The PN11 is a wonderful tube about 52mm in extension and it includes a rotating tripod collar so when added to a lens like the Nikon 105mm macro it gives the landscape-portrait orientation which is so important for much of the macro work that I do. I even use this tube solidly mounted by joining the tripod mounts of PN11 and lens together with my Nikon 200 F4 AF-D Micro Nikkor.

I finally purchased a TC20Eii with the intent of removing the optics and turning into an electrified extension tube. It is superbly made, very robust, has excellent tight F-mounts but the optics are disappointing. Now that Nikon offers the new TC20Eiii which has enormously improved optics the TC20ii is common on the used marketplace – so I purchased one for about $165.00 in E+ condition. I note that Dealers seem to sell these for less than they sell for on EBAY; mine came from KEH.

It only took me about 1 hour to remove the baffles and remove the optics assembly with a spanner wrench, and re-assemble the TC20. If there is a next time it will be faster – it is not a difficult job and vastly simpler than modifying a PN11. It would actually be easy to re-assemble the tube back into a TC20 if there was ever a reason to do so. A few extra minutes to disassemble the lens mount and file off the tab that restricts it for AF-S lenses – as a tube there is no reason to make such a restriction but do realize there is no screwdriver AF coupling – just the AF-S focus system will work.

The modified TC20 tube seems to work as it should using my 70-200 and 300 VR lenses. VR works, AF works, the aperture is reported as 2 stops below actual as set on the lens (as it should be for a 2x teleconverter) and I have not seen any vignetting as the opening is larger than that in the Kenko tubes . And it is built beautifully – by Nikon…..

I note that I have only briefly tested the modified tube and I will be doing more testing over time but not immediately. For those who have been waiting for a good electrified tube and are skilled working with such optical and mechanical components perhaps this is a project of interest. It is not at all difficult if one has the correct screwdrivers and a spanner wrench that fits the optic carrier.

RBFresno
RBFresno Forum Pro • Posts: 12,680
Finally!! A good use for the TC 20 E II!

Interesting!
Kudos to your ingenuity!

And I thought that the Tc 20 E II was next to worthless..

I use the Kenko extension tubes, but even though they work, those suckers feel flimsy!

RB

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Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 17,792
Re: The question is

The question is - why do Nikon not make G type auto extension tubes based on TC14e, 17e and 20e?

While there would be no screwdriver AF drive for pre AF-s lenses, the internal diameter would be wider than Kenko - resulting in less wide aperture vignetting on FX using 300mm and longer primes.
The day Nikon announce them my order goes in.
--
Leonard Shepherd

Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.

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Jeff Loughlin
Jeff Loughlin Forum Member • Posts: 83
Re: A TC20E becomes an electrified extension tube

Nice...I would consider doing this too, but I've gotten used to the PN11 and living without the electronics, so can't justify the cost right now. But I love a good hardware hack, and I just wanted to say good job.

Jeff Loughlin
http://www.pbase.com/jeff_loughlin

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dwa1 Veteran Member • Posts: 4,389
Re: A TC20E becomes an electrified extension tube

Interesting and ambitious project (better you than me).

fwiw... In a recent photo mag, there was an ad for a new "zoom" extension tube.

Thanks for posting your "invention".

Wayne

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OP mmalkin15 Regular Member • Posts: 290
Re: A TC20E becomes an electrified extension tube

Nikon could easily make extension tubes based on the teleconverter bodies without optics. They could improve on the electronics so that the tube does not report 2 full stops below actual aperture and twice the actual focal length as the 2x converter chip does. Thanks to whoever pointed out the availability of a pro-optic variable extension tube for Nikon. I have used variable tubes for high magnification macro work for years - they are far more friendly than using a bellows in the field. I have used Leica threaded versions and Pentax threaded versions as both are available occasionally on the used market and both can be adapted to specialized macro lenses that usually have RMS thread or 39mm leica thread. The Adorama pro-optic tube could be a great find - if it is well made. I may purchase one myself.

joejack951 Senior Member • Posts: 2,682
Re: A TC20E becomes an electrified extension tube

Very good stuff. For those, including myself, interested in something like this, keep in mind that Sigma's EX line of teleconverters are about as well built as Nikon's. I've seen some of their early 2X TC's sell quite cheap on eBay (at the time I was looking for a DG model).

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Marianne Oelund Veteran Member • Posts: 7,779
Eliminating the focal length/aperture change

mmalkin15 wrote:

A TC20E becomes an electrified extension tube

Lenses compatible with teleconverters use the 9th and 10th contacts to detect an attached teleconverter and adjust their reported focal length and aperture.

If you open-circuit one of those contacts on the teleconverter, the lens will report its "native" parameter values instead of double focal length, etc. Not only that, but AF speed will be improved.

OP mmalkin15 Regular Member • Posts: 290
Re: Eliminating the focal length/aperture change

Thanks Marianne! I should have thought to try that but I will definitely experiment and make this change. Do you have any idea if it would be better to make the change on the lens side or on the camera side of the TC20? This is turning into a nice product......

If anyone has any TC14e or TC17e with damaged optics let me know - perhaps they too can be easily converted. Too expensive to purchase a good one for this purpose.

Cheers! Mark

OP mmalkin15 Regular Member • Posts: 290
Re: A TC20E becomes an electrified extension tube

Good thought about using the Sigma converters - I have a Sigma 1.4EX to use with the 150mm macro and it is indeed very robust construction. I will have a look at it.....

Mark

Marianne Oelund Veteran Member • Posts: 7,779
Electrical mod

mmalkin15 wrote:

Thanks Marianne! I should have thought to try that but I will definitely experiment and make this change. Do you have any idea if it would be better to make the change on the lens side or on the camera side of the TC20? This is turning into a nice product......

Mark:

This must be done on the lens side of the TC. The 9th and 10th contacts on the camera side have no function, since the camera lacks those extra contacts.

Just to be clear, the 10th contact will be the one on the far right, as you look into the lens end of the TC with the contacts at the top of the mount, i.e., it's the one closest to the lens release and lock-pin. (The first contact is the one closest to the aperture-control lever.) You only need to open-circuit the 10th contact to make the lens "think" it's mounted directly to a camera body.

Perhaps you could start a little cottage industry, recycling old TC-20E II's! Then, if Nikon introduce updated TC-14 or TC-17 converters later . . .

OP mmalkin15 Regular Member • Posts: 290
Re: Electrical mod

Hi Marianne

You are correct that the aperture is reported correctly when pin 10 is cut but autofocus hunts rapidly back and forth around the proper focal point and cannot lock in at all with my 70-200 - likely too much gain in the motor feedback loop. Restoring pin 10 does restore focus lock operation but yes it is slower. I guess that there is more than meets the eye in the TC20ii electronics - perhaps this is part of the reason that we have not seen electrified tubes from Nikon. I would surmise that the AF algorithm is partly lens specific and may employ distance and lens focus motor characteristic information to control the feedback and work optimally. I should have realized this because I already knew that using the Kenko 36mm tube on the 70-200 has the same AF problem - the lens hunts badly and does not AF. Short extension tubes like the kenko 12mm tube are less problematic but still have a touch of hunting before lock-on. I have previously used the TC14e along with a Kenko12mm tube and was able to get decent butterfly photos. So - using a telconverter or an extension tube seems to require modification and slowing down of the AF operation for AF-S motor lenses .

Still - modifying the converter by removing the optics does work properly but at some cost of AF Performance.

The quest for professionally viable macro AF performance - two steps forward, one step back.....

lucasfunkt Forum Member • Posts: 51
Re: Finally!! A good use for the TC 20 E II!

RBFresno wrote:

And I thought that the Tc 20 E II was next to worthless..

What made you think that!?

RBFresno
RBFresno Forum Pro • Posts: 12,680
Re: Finally!! A good use for the TC 20 E II!

I tried a TC 20 E II on my 200-400VR, 70-200VR I and 200VR.

I was unhapy with the overall IQ (especially withe the first two lenses), and the corners were particularly sub-par.

Now the TC 20 E III is a siginificant improvement over the "II", especially in the corners.

RB

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Marianne Oelund Veteran Member • Posts: 7,779
Re: Electrical mod

mmalkin15 wrote:

You are correct that the aperture is reported correctly when pin 10 is cut but autofocus hunts rapidly back and forth around the proper focal point and cannot lock in at all with my 70-200 - likely too much gain in the motor feedback loop.

Yes, and this is what one expects to happen if pin 10 goes o/c and the teleconverter still has its x2 optics. Apparently, simply adding that much extension to the lens also compromises the AF servo loop stability. That's surprising; I should look into this further next week after I'm back from my photo trip.

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