Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-14-2013, 03:41 AM   #1
Senior Member




Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 273
Physical Dimensions of Pentax K-Mount

So, I have found myself is a little bit of a dilemma. My father has just bought a Sigma SD-1 Merrill, and he wishes to use my small collection of Pentax lenses. I am aware that K-Mount lenses can be mounted directly onto the Sigma SA-Mount, but I am concerned that by cutting/removing the stop down lever on my older Pentax lenses will decrease both their practicality and their resale price if I wish to later sell the lenses.
Therefore, I would like to build a K to SA mount adaptor. Unfortunately, I cannot find the physical dimensions of the k-mount itself (other than the flange distance). Thank you in advance for your help!

08-14-2013, 04:47 AM   #2
Moderator
Site Supporter
Loyal Site Supporter
MarkJerling's Avatar

Join Date: May 2012
Location: Wairarapa, New Zealand
Photos: Gallery | Albums
Posts: 16,204
So far as I'm aware, the SA and K mount is the same size. So, you could build an adaptor from another K-mount ring with the aperture lever removed. This will, of course, alter your focus distance which may not be desirable. Your aperture settings will not transfer through to the camera and the electronic contacts are different, so that may create another obstacle. The rear element in some Pentax zooms may also project too far into the Sigma camera body so you'd have to watch out for that too.
08-14-2013, 05:53 PM   #3
Senior Member




Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 273
Original Poster
So, the gist of what you are saying is that I could purchase an older, possibly scraped lens, and adapt it for use on a sigma mount. So like a Sigma-Pentax-Pentax adaptor, but with the middle adaptor having the aperture lever removed? Would this possibly compromise access to infinite focus, or would it just increase the focal range?
Thanks for the swift reply!
08-14-2013, 06:35 PM   #4
Moderator
Site Supporter
Loyal Site Supporter
MarkJerling's Avatar

Join Date: May 2012
Location: Wairarapa, New Zealand
Photos: Gallery | Albums
Posts: 16,204
The registration distance on Pentax is 45.6mm and on Sigma SA-Mount it's 44mm so, yes, there will be some issues with focus, but in reality what you're having is a very short macro extension tube, so focussing should not be your main issue. I'd say a bit of experimenting may answer your question as to focus changes.

The bigger difficulty is controlling the aperture. You'll have to do manual metering. As noted, the camera will no longer receive the correct data from the lens so it will be as if you're working with a completely manual lens.
Like you, I would avoid cutting the aperture lever of a perfectly good Pentax lens, so attempting an adapter is certainly the only way to go. If it's not successful, it's no great loss - Your Pentax lenses will still be fine!


Last edited by MarkJerling; 08-21-2013 at 04:40 PM.
08-14-2013, 06:39 PM   #5
Senior Member




Join Date: Jul 2013
Location: Melbourne
Photos: Albums
Posts: 273
Original Poster
Thanks for the advice you have given me. My father has only just moved into Digital photography, but he's quite the wiz when it comes to guesstimating settings, so I am sure he will be able to adapt to the circumstances. Also, I wasn't planning on using any new DA lenses on the camera, only older lenses with aperture rings such as Pentax K, A and M lenses. Thanks for the speed re-reply!
08-14-2013, 07:40 PM   #6
Moderator
Site Supporter
Loyal Site Supporter
MarkJerling's Avatar

Join Date: May 2012
Location: Wairarapa, New Zealand
Photos: Gallery | Albums
Posts: 16,204
QuoteOriginally posted by Joshua A Quote
Thanks for the advice you have given me. My father has only just moved into Digital photography, but he's quite the wiz when it comes to guesstimating settings, so I am sure he will be able to adapt to the circumstances. Also, I wasn't planning on using any new DA lenses on the camera, only older lenses with aperture rings such as Pentax K, A and M lenses. Thanks for the speed re-reply!
My pleasure. I hope it works OK! Let me know how you get on with the adapter.

Kind regards,
Mark
08-15-2013, 05:04 AM   #7
Moderator
Site Supporter
Loyal Site Supporter
MarkJerling's Avatar

Join Date: May 2012
Location: Wairarapa, New Zealand
Photos: Gallery | Albums
Posts: 16,204
Have thought about this further. The best route, probably, would be a very short extension tube, like the type used for macro photography, only shorter. You could therefore buy either an extension tube and butcher that, or a doubler, and butcher that. The trick would be to keep the inbetween bit (the mount adapter you create) as 'short' as possible, so as not to change the focal distance too much. It would need to be long enough to accommodate the lens aperture lever without scraping against the back of the mount when installed to the camera.

08-21-2013, 02:36 PM   #8
Pentaxian
scratchpaddy's Avatar

Join Date: Feb 2013
Location: Phoenix
Posts: 2,960
Mark's given good advice, but I have some details to add.

First, the Sigma mount is identical to Canon's except for the bayonet, which is copied from K-mount. If you were to replace the bayonet with a Canon one, Canon lenses would work with full functionality: auto-aperture, autofocus, everything. That's what I've read, anyway.

Also, M42 lenses are even easier to adapt to Sigma than to Pentax. Since Sigma's registration distance is shorter, as Mark pointed out, you can use those flanged adapters and still get infinity focus. You still want to get one that has a rim to catch the aperture pin on those lenses, though. Those are harder to find.

Good luck! Have you tried anything yet?
Reply

Bookmarks
  • 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!
dimensions, k-mount, lenses, pentax, sigma
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
adapters for non-K-mount lenses to Pentax K-mount DSLRs: new dimensions for LBA Douglas_of_Sweden Pentax Camera and Field Accessories 154 07-10-2020 10:57 AM
Need dimensions of HOOD for Tele-Takumar 300mm f6.3 cheekygeek Pentax SLR Lens Discussion 5 06-14-2013 08:54 AM
Photos of K and M42 mount variations (photos of pentax k-mounts) Just1MoreDave Pentax Lens Articles 11 12-06-2012 12:14 PM
K-5 physical size stormtech Pentax K-5 & K-5 II 20 07-22-2011 07:33 AM
Need words of wisdom from users of T-mount adapter for K mount. Graystar Pentax SLR Lens Discussion 5 01-27-2010 05:21 PM



All times are GMT -7. The time now is 09:17 AM. | See also: NikonForums.com, CanonForums.com 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?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top