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02-17-2015, 02:53 PM   #91
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QuoteOriginally posted by Rorschach Quote
How hard can it be?
I think that the main problem is the screw-drive functionality.

Especially if you have three tubes stacked,
that makes a lot of joints to introduce slop,
which is not good when AF relies on back-and-forth "bracketing" movements.
QuoteOriginally posted by Rorschach Quote
While you are at it, make them weather sealed too!
A nice idea, but the sealed joints would make assembling the rig that much harder.

02-17-2015, 03:05 PM   #92
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QuoteOriginally posted by lytrytyr Quote
I think that the main problem is the screw-drive functionality.

Especially if you have three tubes stacked,
that makes a lot of joints to introduce slop,
which is not good when AF relies on back-and-forth "bracketing" movements.


A nice idea, but the sealed joints would make assembling the rig that much harder.
I understand the problem with joints but it would be easy to just make one long tube that would be the same length as the three regular ones combined. No joints, no problems, also with WR seals!
02-17-2015, 03:16 PM   #93
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QuoteOriginally posted by Rorschach Quote
it would be easy to just make one long tube that would be the same length as the three regular ones combined.
That could be too much extension for a lot of situations.
I often end up just using a single one of the shorter (manual) tubes.
02-18-2015, 06:54 AM   #94
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I don't think it is a problem (AF, weather sealing) and yes, they most probably will produce those (but the price will set you off).
They may not have AF (which really is not *that* important for tubes) but A contacts though, certainly.

02-18-2015, 10:27 AM   #95
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QuoteOriginally posted by thibs Quote
I don't think it is a problem (AF, weather sealing) and yes, they most probably will produce those (but the price will set you off).
They may not have AF (which really is not *that* important for tubes) but A contacts though, certainly.
Maybe they will produce those one day, but meanwhile, sparked by grahame's idea, I think I found a semi-elegant-hack-job-solution:
https://www.pentaxforums.com/forums/37-wanted-items/289048-wanted-extension-t...utomatics.html

Those Pentax Takumar teleconverters have electrical contacts and seem to go for much less than SMC ones. Perhaps others want to experiment as well :-)
02-17-2016, 09:07 PM - 1 Like   #96
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Hi,

Sorry to resurrect an older thread, but I noticed that the "Kooka" tube is available from an Aliexpress seller:

http://www.aliexpress.com/item/AF-Auto-Focus-PK-Macro-Extension-Tube-Ring-Fo...ddresstype=600

Also, that same seller has this other set:

http://www.aliexpress.com/item/AF-Auto-Focus-PK-Macro-Extension-Tube-Ring-Fo...00009.1.DUYMxA
02-18-2016, 03:52 AM   #97
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that looks a lot like the 25mm Extension tube I have:





This is the one I have:
02-18-2016, 10:20 AM   #98
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Yes, the Kenko Uniplus tubes work great with screwdrive AF and even SDM.

I got mine for 30 EUR off ebay. It's really good for usie with macro lenses or the DA*300 for semi macro work.

02-18-2016, 11:47 AM   #99
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Hi,

I have some "dumb" extension tubes, that, when I remove the paint off of part of the rim (to short the contact next to the screw), allow the camera (K-r) green button to work and Av also. If I don't short that contact on the body (the lens mount), green button and the Av don't work correctly.

So I'm looking at this one:

Asahi Pentax Teleconverter 2X Takumar A for Pentax A Light Haze 184795 | eBay

Assuming I removed the glass, would that work and let the AE work without doing any paint scraping? I notice that that one appears to be missing the contact next to the screw.

Thanks,
Jim
03-06-2017, 01:34 AM - 1 Like   #100
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How to convert a Kooka KK-P25 AF extension tube to something useful

Thought I'd resurrect this thread because I just bought a Kooka KK-P25 and found a way to be happy with it. Parts first posted over at dpreview.

Problems with the tube

I got three major gripes with the Kooka KK-P25:
  • First annoying thing is that it includes a aperture simulator lever - not used by DSLRs - that is not spring loaded (which is very unusual for tubes or converters - all other I have do sport a spring loaded simulator). It floats freely inside the tube, and to mount a lens you have to rotate the tube to an angle that forces the lever to go to a fixed position at one end - and only then you can mount a lens (they include a small leaflet in the package that explains what you have to do).
  • Second annoying thing is that the screwdrive coupling is very poorly made. If you switch to MF on your camera, the screwdrive pin of the tube does not disengage from the lens, and manual focusing of AF lenses is hampered by this (and accompanied by very unsettling, grinding noises).
  • Third annoying thing is again the screwdrive coupling that is - as I said before - very poorly made and machined. At least with my copy of the tube it was a hit and miss thing to get the camera's AF screw to grab the tube's clutch securely. I tried it on multiple bodies - K-1, K-5, K-10, Ds and K-01 - and on all of them it rarely worked after mounting - most times it did not; in those cases the AF motor of the camera whirred in high pitch without achieving anything - not a sound you want to hear too often ...
Apart from that it was hard to achieve correct focus even if the screwdrive clutch engaged successfully; with PDAF most times focus was missed all the same, and only using live view with CDAF focus was usable; even then you got more hunting than usual IMO.

So what to do with that Kooka contraption?

How to convert the tube to something useful

I still wanted to have a tube with K-mount data and aperture contacts, since the manual tubes I already got force you to use stop down metering - this IMO is really not that comfortable in close up and macro photography. I wanted to use it mainly with my FA50/1.4 and my Samyang 85/1.4 - both nice bright primes, but with not so nice minimum focusing distances and because of that good matches for a tube.

So I decided to lose the useless aperture simulator and the unreliable screwdrive coupling. And that turned out to be a painless five minute thing to do. Here's how to do it (I forgot to take pictures while "operating" on the tube, but it's really easy):
  1. Place the tube on its flat front (lens side), so that you look at its back side (camera or mount side) with the aperture control lever looking at you (not to be confused with the aperture simulator lever ...)
  2. Now remove the three outer screws of the mount (the three inner ones on the black part of the mount stay untouched) and slowly and carefully pull the central mount element from the tube. It takes a bit of wriggling, but you'll get it free eventually.
  3. After removing the central element you will quickly spot the freely roaming aperture simulator lever. Be careful: don't confuse it with the aperture control lever that is needed to stop down the lens! If you're unsure about that have a glance at this article about the K-mount - skip to the section with the title "The original K-lens mount as introduced in 1975" and look at the first picture in this section to identify the levers.
  4. Now back to the simulator lever of the tube; it's attached to a metal plate with two tiny small black screws. Remove those two screws - now you can get the annoying simulator lever and throw it away. You won't miss it! Unless of course you want to use the tube with an old film body - in that case save the lever and the screws for attaching them again when needed. The metal plate will still move around in the tube causing some noise now and then, but won't interfere with lens mounting any more.
  5. Now for the screwdrive coupling: The upper part of the coupling you can remove by hand; but since it's spring loaded you need a pair of pincers to get the small spring below it and to remove the remaining part - the clutch - from the recesses of the tube. Again save everything if you want to re-install it - I was appalled by it's unreliable operation so I didn't hesitate to throw it away.
  6. Then carefully re-attach the central mount element, fasten its three screws - and you're done!
You now have a cheap, but good working extension tube that has no AF, but allows for smooth MF and provides all other K-mount contacts you need to work with automatic exposure modes. And that sure is a nice thing to have for 25 Euros and 5 minutes of work!

Of course you have to do the conversion at your own risk - it went smoothly in my case, but I can't guarantee it for other copies of the tube.

One last thing: I couldn't test if the tube's SDM pins work properly since I don't have a SDM lens.

Feel free to ask any questions.
04-18-2017, 05:33 PM   #101
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Find a used or old-stock-NIB third-party teleconverter for Pentax A or film-era Pentax AF (they exist) and deglass it. Some of them are PK-A/R and have the Ricoh Pin, but this is easily dealt with, and the finer and more upmarket models have the rounded pin and are benign.

Last edited by Racer X 69; 04-19-2017 at 01:06 PM.
04-18-2017, 06:08 PM - 1 Like   #102
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QuoteOriginally posted by pathdoc Quote
Find a used or old-stock-NIB third-party teleconverter for Pentax A or film-era Pentax AF (they exist) and deglass it. Some of them are PK-A/R and have the Ricoh Pin, but this is easily dealt with, and the finer and more upmarket models have the rounded pin and are benign.
Amongst other factors, 2X teleconverters are generally 25mm long at least, and so obviously can not replace a 9 or 11mm extension tube, for example.

Last edited by Racer X 69; 04-19-2017 at 01:07 PM.
04-18-2017, 10:30 PM   #103
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Of course, this will only net an extension tube of about 25mm in length. Not really sure what to do for other lengths.

Last edited by Racer X 69; 04-19-2017 at 01:09 PM.
04-19-2017, 03:53 PM   #104
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t/c's have small holes compared to conventional extension tubes = vignettes on ff (depends on lens, amount of extension). if you use a deglassed t/c in conjunction with conventional extension tubes, make sure it goes close to the lens, not the body.
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