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Ramon
Joined: 01 May 2007
Posts: 71
Location: Kent, UK
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 Posted: Sun Nov 10, 2013 2:52 pm Post subject: PK to EOS adaptor with aperture control |
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Ramon wrote:
Well after 2 days of effort, stretching my poor engineering skills to the limit I have sort of achieved it.
I have modified a PK to EOS adaptor so that it has semi-automatic aperture control.
I think the pictures speak for themselves but the principal is a small spring cam lever that holds the lens aperture lever in the wide open position. Once you have focussed at full aperture then a press on the cam will release the lever to the pre-set aperure.
For a new exposure you adust the lens aperture ring to full aperture which engages the lever back into the cam, then select the desired aperture again ................
By having a stepped notch on the end of the cam I have made it work with original Pentax K and Pentax M lenses.
It sort of works with Pentax A lenses but these have a lever movement that is proportional to the aperture so that the lever a large aperture lens will fall in a different position to one having a small aperture when set wide open, this would either need a multi stepped cam or a cam that could be adjusted to suit the lens.
Anyway I have achieved my aim, I've proved it can be done and mine works although it's a bit flimsy and crude. All it needs now is for someone with better engineering skills to do a bit of developement. Of course whether it would be practical to manufacture these is another matter |
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casualcollector
Joined: 01 Aug 2008
Posts: 750
Location: Spaced out on Florida's Space Coast
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| Posted: Sun Nov 10, 2013 3:05 pm Post subject: |
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casualcollector wrote:
Clever! Bravo 
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philslizzy
Joined: 07 Aug 2012
Posts: 4745
Location: Cheshire, England
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| Posted: Sun Nov 10, 2013 10:56 pm Post subject: |
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philslizzy wrote:
Pretty ingenious solution I guess this will work with any PK lens.
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Ramon
Joined: 01 May 2007
Posts: 71
Location: Kent, UK
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| Posted: Mon Nov 11, 2013 1:38 pm Post subject: |
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Ramon wrote:
| philslizzy wrote: |
| Pretty ingenious solution I guess this will work with any PK lens. |
Well I have tested it with:
Pentax K 35mm 3.5
Pentax M 28mm 2.8
Pentax M 28mm 3.5
Pentax M 50mm 1.7
Pentax A 50mm 2.8 macro
Pentax K 135mm 3.5
The only one that isn't too clever is the 50mm A, instead of holding the lens wide open it holds at about f3.5.
Another step in the cam would have cured this but the precision required was beyond my engineering skills.
All of the others work perfectly. |
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mo
Joined: 27 Aug 2009
Posts: 8979
Location: Australia
Expire: 2016-07-30
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| Posted: Tue Nov 12, 2013 12:20 am Post subject: |
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mo wrote:
I have moved this to the DIY section of the forum...excellent adapter, it may inspire others. 
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tromboads
Joined: 29 May 2012
Posts: 1655
Location: Melbourne AU
Expire: 2015-10-01
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| Posted: Tue Jan 21, 2014 11:25 am Post subject: |
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tromboads wrote:
That's a nifty little Idea  Well done. |
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RSalles
Joined: 12 Aug 2012
Posts: 1372
Location: Brazil - RS / South
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| Posted: Tue Jan 21, 2014 11:53 am Post subject: |
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RSalles wrote:
Hi,
It would be great to have a template for this, I could go to a CNC equipped technician and make 500 in 1/2 of an hour!
1US$ per each can make US$500.00 - minimum quantity: 5 - to make it go faster.
Cheers,
Renato |
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ZoneV
Joined: 09 Nov 2009
Posts: 1632
Location: Germany
Expire: 2011-12-02
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| Posted: Tue Jan 21, 2014 4:36 pm Post subject: |
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ZoneV wrote:
Great modification for this adapter!
Good idea!
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