Kenko extension tube problem

[Gagili]

First of all, I want to say hello to everyone on the forum.

My first post and don't mind if the topic is in the wrong place. I looked where I could open a thread and it seems fine here.

I have a problem with the Kenko Auto Extension Tube Set DG for Nikon F Mount. The camera they use is Nikon D780 with a lens Nikon AF-S 24-120mm f/4G ED VR.

The problem is in the autofocus when using focus stacking.

.When each of the tubes is used separately, the autofocus works. But if I use two or all three tubes, it doesn't work. I have read a lot about the possibilities of why this is so.

But I don't understand one thing. If I set only the 36mm tubes, the AF works. However, if I put the 12mm and 20mm tubes together, it doesn't work. The distance from the sensor is similar. The amount of light according to the sensor is almost the same. Contrast, too.

Then why doesn't it work?

When they are separate, each tube works. However, it does not work in any combination with 2 or 3 tubes.

I would really appreciate an answer.

And don't mind the English. Because I write to the user a little of my knowledge and google translator.
 

[paddler4]

Usually, the reason would be low light. However, I can't answer why you have a problem with 12+20 but not with 36mm. My guess is that the electrical contact is weak and that having two tubes makes this worse.

[William Michael]

8 hours ago, paddler4 said:

Usually, the reason would be low light. However, I can't answer why you have a problem with 12+20 but not with 36mm. My guess is that the electrical contact is weak and that having two tubes makes this worse.

My thoughts too.

Maybe the middle connection is poor i.e. the connection between the two tubes - perhaps identified by the tubes being able to be wobbled.

WW 

[Gagili]

Thank You for the answers.

It could very esily, as You say, a problem with the contacts. I measured the resistence. It has no lasting value. All the time value varies. At no point was it a constant value.

I plan to open one ring and see what and how it was done with the contacts. As well as whether there is a possibility for a firmer and more stabile connection.

[paddler4]

I vaguely remember that years ago, after years of heavy use, one of my three Kenko tubes got loose and no longer had a reliable connection. I replaced the set, so now I have 5....

[Gagili]

Yes. Connections are a problem. I didn't doubt it that much. I thought more that there was something from the electronics, so that was the problem.

However, yesterday I opened only one side, two rings. The thinnest and medium. The side where the contacts inside the ring are accessible.

I can tell you that I am quite disappointed. It was done so precariously. The contacts are simply placed on the ends of the ribbon flat cable.

The thickest ring has a resistance between contacts of slightly less than 1 ohm. On the other two I managed to reduce the resistance, when they are together, to about 4 ohms.

But again it's not worth it. It seems that this value is not suitable for the electronics of the device.

Honestly, I started thinking about opening the other side as well. Where are the external spring contacts. Let me see what the construction is like. Well, if it is possible to solder a thin cable. My only doubt is the temperature of the soldering iron tip. To prevent the plastic from melting and weakening the grip around the contact.

But I will consider that in the coming days.

[Gagili]

Oh guys, I think I get what you're talking about. At least I hope so.
Yes, it is about contacts. But apparently not about their resilience.
Something did not give me peace and I did not want to start remaking the Kenko rings.
I looked on the Internet and noticed that Kenko has 7 electrical contacts. But Meike has 8. I looked for the reason why, and what the contact was responsible for.
I found it on a site.
The eighth contact is responsible for the ground of the AF-S lens. The seventh is ground, but the eighth is stated to use AF-S lenses.
And I have AF-S lenses in my possession. It will be good if that is the solution. I didn't pay attention to it until now, but I tried to find the reason. In a few days I will order Meike and see what happens.
Of course, I will inform you in any case. So that you also have information for sometime if you need it.

Contact information from the site. I do not list the site so that it is not an advertisement.

1. VCC (power)
2. RW or H/S (read/write) (becomes RW1 if teleconverter is used)
3. LCLK (serial clock) (becomes LCLK1 if teleconverter is used)
4. LIO (serial data) (becomes LIO1 if teleconverter is used)
5. (teleconverter use) RW2
6. (AF-S use) LBAT
7. PGND (ground)
8. (AF-S use) PGND (ground)
9. (teleconverter use) LCLK2 (serial clock)
10. (teleconverter use) LIO2 (serial data)
The odd teleconverter extra (all the "2") signals allow the lens to talk simply through the teleconverter. The teleconverter only responds to the lens with a 1.25, 1.4, 1.6, 1.7, or 2x value, which the lens then processes and alters the focal length and aperture parameters in communicating with the camera on the main signals ("1" signals). 

The full AF-S focusing protocol is described in US patent 5727241.

[PapaTango]

I sent 2 sets of the Kenko tubes back to Amazon years ago.  The build quality was just not there and intermittent electrical issues with stop and focus were present.  Yes, I cleaned all contacts, checked them out on my DMM, and problems persisted once on the camera body.  I have found the Meike and Xit to be much better solutions.

At issue seems to be the material that the springs inside the contact tips are made from, and the fact that construction is cheap.

Remember Spiratone?  🤔

 

[William Michael]

4 hours ago, PapaTango said:

Remember Spiratone? 

Yes, I do; and Makina Optical, especially their Makinon 28~80 zoom.

We two must have an similar age zoom compass. 

Regards.

On 5/13/2024 at 10:13 PM, Gagili said:

In a few days I will order Meike and see what happens.
Of course, I will inform you in any case. So that you also have information for sometime if you need it.

I hope that works for you.

WW

[Gagili]

@PapaTango, yes, it also proved to be a better solution for me.

@William Mishael, thank You.

As I promised, let me write a few words.

I received a package of Meike extension tubes today.
Tried various combinations. unlike Kenko, only all three together did not want to work.
At 50mm zoom, I couldn't get close enough to get sharpness. With 80mm and above, any combination except all 3 together, worked.
I can say that I was really surprised how quickly it sharpened.

Let me explain what happens when all three are together.
On the camera back screen, there is a red square. When sharpened, it turns green. In this case, it looks like it would change color, but it doesn't. You can see a momentary change to some shade of red, towards yellow. And don't sharpen.

Honestly, I'm satisfied with this as well. this is already a completely different situation in relation to Kenko.
I will see how it will be with the lens AF-S 70-200mm f/2.8E FL ED VR. It is planned for purchase near the end of this year.

At the same time, I would like to thank You for reading and answering.