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08-15-2017, 01:16 PM   #1
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Extension tube PK-A conversion?

Hi all;

Extension tubes with A series contacts are scarce and expensive. I was wondering if anyone out there has ever taken a PK extension tube and converted it to a PK-A version using parts from a PK-A teleconverter? I've got de-glassed teleconverters for longer focal length lenses, but using them on w/a lenses results in the focus point being inside the lens. I'm hoping that PK-A-ing the 12mm tube from the set of three will let me do some ultra wide angle macro. I've got a set of PK auto extension tubes and a surplus PK-A TC to use as a parts donor. I would like to convert the shortest tube to PK-A, but I don't possess the tools or skills to do it myself. Does anyone out there do this sort of work?

Thanks,

Bruce

08-15-2017, 01:35 PM   #2
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That's a pretty clever idea- I'm also curious to hear if it's been done before!

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08-15-2017, 02:09 PM - 1 Like   #3
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Before you invest time and money in the project, you might want to double check the max extension tube length that your UWA lens can handle before the focus point slips into the lens. TO do that, hold the dismounted lens so that the front element is just touching something easy to focus on such as a pencil tip and then free-lens the camera to find the gap that brings the pencil tip into focus. That gap is the biggest tube you could take.

And if you really want to hack your own A-tube, then get any cheap/broken A-series lens and any cheap/broken A-series camera and attach the bayonet from the lens to the mount from the camera with all the little A-contact magic stuffed between them.
08-15-2017, 02:15 PM   #4
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IME close-up and macro photography is so slow and deliberate in both planning and execution that I've never considered automation for focus or exposure to be advantageous.

OTOH, simple manual extension devices lend themselves to experimentation and DIY lens mount adapters that would be unavailable or prohibitively expensive if purchased.

Given the tremendous advantages of post-shot histogram and DOF review my only attempt to automate macro exposure was to de-glass a TC for use in a particular remote shooting situation. Today, tethering might be an even better answer.

08-15-2017, 02:16 PM   #5
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I find WA lenses usually need to be reversed to focus when used on tubes or bellows. Reversing the lens will wipe out any functionality of the contacts.
08-15-2017, 02:47 PM   #6
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Thanks for all the responses. Sounds like the hack would be trickier than I'd hoped; oh well.

The lens I had in mind to use is the Sigma 10-20, which has no aperture ring, hence the desire for A contacts.
08-15-2017, 03:11 PM   #7
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Pentax Hacks: Hacking a Pentax K teleconverter to an A

There are a couple of threads here on PF also looking at this sort of hack.

08-15-2017, 03:28 PM   #8
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Kenko AF extension tube is pretty inexpensive and makes the job done.mine( AF 25) costed something like 30euro on Ebay.
08-15-2017, 03:42 PM   #9
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The Kenko works for me. But the usual way to attain what you want is to remove the glass from an A teleconvertor, and voila, you have an A extension tube.
08-15-2017, 04:53 PM - 1 Like   #10
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I did buy a Vivitar 2 x 1:1 Macro extender broken on ebay for about ten bucks and took out the bad lens out. It makes a variable extension tube with A contacts.
08-16-2017, 01:47 AM - 1 Like   #11
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QuoteOriginally posted by Dentax Quote
I did buy a Vivitar 2 x 1:1 Macro extender broken on ebay for about ten bucks and took out the bad lens out. It makes a variable extension tube with A contacts.
Did a similar conversion a few months ago myself.....



.
08-25-2017, 02:53 PM - 1 Like   #12
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Dare I suggest that if the OP can't find a suitable TC/lens to mod, a decent +1/+2 Close-up lens might be a possible (albeit relatively expensive!) alternative as that would hopefully retain the AF facility (if that is considered important)?
08-25-2017, 04:43 PM   #13
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A close-up lens is certainly worth considering.

It's not the AF that's important but aperture control. The Sigma in question has no aperture ring so anything between it and the camera body that doesn't have the A contacts leaves me relegated to wide open, unless I want to jam something into the aperture control lever mechanism to close it down before I mount it to the camera.
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