Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
08-15-2017, 01:16 PM   #1
Thagomizer's Avatar

Join Date: Jun 2014
Location: London Ontario
Posts: 1,926
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?



08-15-2017, 01:35 PM   #2
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 50,349
That's a pretty clever idea- I'm also curious to hear if it's been done before!

Adam Webmaster (Site Usage Guide | Site Help | My Photography) server and development costs are user-supported. You can help cover these costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

08-15-2017, 02:09 PM - 1 Like   #3
photoptimist's Avatar

Join Date: Jul 2016
Photos: Albums
Posts: 4,726
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
Loyal Site Supporter
Loyal Site Supporter
pacerr's Avatar

Join Date: Jan 2008
Location: Paris, TN
Photos: Gallery | Albums
Posts: 3,192
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
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 8,740
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
Thagomizer's Avatar

Join Date: Jun 2014
Location: London Ontario
Posts: 1,926
Original Poster
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
Site Supporter
Site Supporter

Join Date: Nov 2012
Location: North Wales
Photos: Gallery | Albums
Posts: 2,556
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
Veteran Member

Join Date: Aug 2014
Location: Italia
Photos: Albums
Posts: 354
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
Veteran Member

Join Date: Jul 2009
Photos: Albums
Posts: 392
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
New Member

Join Date: Dec 2012
Posts: 22
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
LennyBloke's Avatar

Join Date: Aug 2008
Location: Worcestershire, UK
Photos: Gallery
Posts: 577
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

Join Date: May 2008
Location: London, UK
Posts: 1,509
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
Thagomizer's Avatar

Join Date: Jun 2014
Location: London Ontario
Posts: 1,926
Original Poster
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.

  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
extension, extension tube pk-a, extension tubes, lenses, macro, macro extension tubes, macro tubes, pk, pk-a, teleconverter, tripod, tube, tubes
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Pre deglassed PK/A autofocus auto aperture extension tube kernos Pentax SLR Lens Discussion 7 10-07-2016 03:31 PM
Extension tube PK mount pixie Pentax Camera and Field Accessories 14 11-07-2013 07:17 AM
My new(old) SDM Extension Tube conversion philbaum Pentax SLR Lens Discussion 3 01-22-2012 01:07 PM
For Sale - Sold: Tamron 90mm 2.5 W/ extension tube & PK/A adapter, Pentax A 50mm f1.4 and misc. OrenMc Sold Items 22 11-26-2011 03:33 AM
For Sale - Sold: PK-A AF extension tube (US) pcarfan Sold Items 2 12-16-2010 03:53 AM

All times are GMT -7. The time now is 04:36 PM. | See also:, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]