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Thread: Pentax 110 lens adapter for the G1

  1. #1
    ChrisJ
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    Pentax 110 lens adapter for the G1

    For the last week I've been pondering using the Pentax 110 lenses on the G1, the problem is, as you all know, that there is no aperture adjustment on these lenses, but they are optically superb.

    Heres my design criteria,

    It must be able to focus on infinity.

    Be able to change aperture without removing the lens off the camera.

    Be fairly strait forward to make.

    Use any available Pentax 110 lens.

    I found that to avoid vigneting the aperture had to be directly behind the lens as it was in the original camera. There is not really enough room to fit a conventional aperture mechanism behind the lens.

    As every different focal length needs a different sized hole for say f8 it wouldnt be easy to calibrate a normal aperture mechanism.

    After a lot of midnight oil I finally hit on the idea that the really old turn of the century photographers used and make slide in apertures. These are made of Plasticard which is available in thin sheets, in black and is cheap.

    Here are some first results, all are shot with the lens focussed on the front red berries at their closest focussing wide open, the focus wasn't changed when stopped down ;-

    First the 18mm lens wide open (f2.8)



    Then with a 2mm diameter aperture




    The 24mm lens wide open (f2.8)



    With the same 2mm aperture



    Finally the 50mm lens wide open (f2.8)



    and with the same 2mm aperture which on this lens is about f25 !!



    I'll post pics of the adapter if anyone is interested.

    Chris
    Last edited by ChrisJ; 26th September 2009 at 16:41.

  2. #2
    Abbazz
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    Re: Pentax 110 lens adapter for the G1

    Quote Originally Posted by ChrisJ View Post
    I'll post pics of the adapter if anyone is interested.
    Thanks Chris for the superb pictures. Those miniature Pentax lenses are so cool!

    I would be very interested in your pictures of the adapter, because I have a few of these lenses: 18mm, 24mm and 70mm. I also happen to have the Soligor 2x teleconverter, which has a fixed diaphragm ring giving an aperture of F/8. It might be an easy way to get a reduced aperture with the telephoto lenses, if optical quality is on par, which I haven't tested yet.

    Cheers!

    Abbazz

  3. #3
    Member slosync's Avatar
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    Re: Pentax 110 lens adapter for the G1

    Nice results for the 2mm hole... I think you're onto something there Chris. I was thinking along those same lines except trying to think how one might "snap", twist, stick or glue(worst case) a specific sized hole on to the bottom of the lens. There seems to be room for a small metal or plastic cap to fit over the end on the rear element with an appropriate size hole for aperture contol.

    Anxious to hear/see some of your followup advances on your sliding plastic aperture control idea.

    Thanks and cheers,
    Don
    Last edited by slosync; 26th September 2009 at 17:42.

  4. #4
    wblynch
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    Re: Pentax 110 lens adapter for the G1

    Wow.

    Each one of those lenses have beautiful sharpness and color rendition.

    Especially when "stopped down".

    The 18 wide open has some crazy bokeh, though.

    Thanks for posting.

    -Bill L.

  5. #5
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    A few pics of the adapted adapter as promised. It started off as an RJ M39 adapter (it can still be converted back if needed). The centre was removed (3 screws) and replaced with a black Delrin - well a thick washer really, with the bayonet mount from an old Pentax Auto 110 fitted. Behind this, directly behind the lens, a 'pocket' is made from a lamination of 2 pieces of black Plasticard. Where this 'pocket' matches the side a slot has to be milled in the adapter to allow the aperture to enter the 'pocket', this is the difficult bit.



    When fitted to the G1 it looks like this;-



    Note the offset to avoid the false 'prism hump'.

    The apertures are just some Plasticard with a semicircle on one end with the aperture centred in it, this is centered behind the lens by the 'pocket'.



    Here it is half in and half out to show the idea.



    The whole delrin 'washer' can be moved backwards and forwards in the adapter to collamate the setup, it's very critical, fractions of a mm make all the difference. Then you just tighten the 3 screws in the RJ adapter to lock it all together.

    Not an ideal solution, but it works very well.

    Chris
    Last edited by ChrisJ; 27th September 2009 at 05:09. Reason: additions

  6. #6
    vlatko
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    Re: Pentax 110 lens adapter for the G1

    Interesting work. Pity about that double bokeh wide open. :-)

    I'd also expect a significant amount of difraction blurring at F25...

  7. #7
    Senior Member m3photo's Avatar
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    Re: Pentax 110 lens adapter for the G1

    [QUOTE=ChrisJ

    The apertures are just some Plasticard with a semicircle on one end with the aperture centred in it, this is centered behind the lens by the 'pocket'.

    [/QUOTE]
    Thank you Chris, I'll have a go when I get time. Just an addition to your great idea - you can have two apertures on the "Plasticard": have both ends cut in a semicircle and drill a 2mm "aperture" on one end and a 3mm one on the other. This way you get roughly an f4 for your 18mm on this other end and it's probably an f11 on your 50mm (only guessing here - haven't got a clue about the mathematics of it) - just flip to taste

  8. #8
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    Good idea about the 'double endings', two for the price of one.

    The maths are simple, it's just focal length / aperture = hole diameter (as focal length is in mm so is the hole size).

    Chris

  9. #9
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    Quote Originally Posted by vlatko View Post
    I'd also expect a significant amount of difraction blurring at F25...
    Do you see any?

    Chris

  10. #10
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    Re: Pentax 110 lens adapter for the G1

    That's execellent. Quite a neat idea.

  11. #11
    Abbazz
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    Re: Pentax 110 lens adapter for the G1

    Great job Chris, the adapter looks very well done.

    I shall post a few pictures as soon as I get an adapter for my lenses. The 70mm at F/2.8 should be interesting and I want to try this 2x teleconverter...

    Cheers!

    Abbazz

  12. #12
    Senior Member m3photo's Avatar
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    Re: Pentax 110 lens Teleconverter

    Quote Originally Posted by Abbazz View Post
    ... and I want to try this 2x teleconverter...
    The Soligor is a 1.7x teleconverter.

  13. #13
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    I'm looking forward to seeing your pics Abbazz, the 70mm is the one lens I don't have, oh and the teleconverter.

    Chris

  14. #14
    Abbazz
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    Re: Pentax 110 lens Teleconverter

    Quote Originally Posted by m3photo View Post
    The Soligor is a 1.7x teleconverter.
    You are right, it's a 1.7x Teleconverter. Sorry for the mistake.

    Cheers!

    Abbazz

  15. #15
    vlatko
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    Re: Pentax 110 lens adapter for the G1

    Quote Originally Posted by ChrisJ View Post
    Do you see any?
    Sorry, clumsy grammar. It should have read "I would have expected..."

    No diffraction and that surprised me.

  16. #16
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    Thanks Vlatko, you had me looking for it just then LOL.

    Chris

  17. #17
    Member laptoprob's Avatar
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    Re: Pentax 110 lens adapter for the G1

    I have the 18 and 24mm mini lenses coming my way. Searching around I found this thread. The advantage of being able to use an aperture is obvious, but in the examples above I see quite a lot of vignetting. The Pentax 110 cameras have a square aperture/shutter assembly. I guess using a round aperture can cause the vignetting. If I want to hack something, should I use a square aperture then?
    Or is the vignetting caused by having the aperture hole not perfectly centered?
    In another thread I saw an aperture assembly put between the lens and camera. Does that setup vignette too?
    "You live and learn; at any rate you live" (Douglas Adams)

  18. #18
    duckrider
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    Re: Pentax 110 lens adapter for the G1

    Hello, my name is Thomas, living near Wiesbaden/Germany and this is my first post in this forum, so a kind "Hello Everybody from Germany"!

    @ChrisJ:
    YOU are the reason for me to enter in this forum, Your Adapter with variable diaphragm settings is a dream, that's what I was looking for.
    Many many thanks for Your minutely description, Pentax & Adapter for tinkering are ordered

  19. #19
    Senior Member m3photo's Avatar
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    Re: Pentax 110 lens adapter for the G1

    Quote Originally Posted by ChrisJ View Post
    When fitted to the G1 it looks like this;-

    Are you selling these? If so, please drop me a line, thanks.

  20. #20
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    Welcome to the group Thomas, that's the kind of feedback that keeps us going - thanks.

    Chris

  21. #21
    ChrisJ
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    Re: Pentax 110 lens adapter for the G1

    Sorry Michael, one was enough for me. Having said that I am still experimenting, the original adapter just held the lenses by friction (hardly ideal), I would really like a spring loaded positive lock implemented, thinking cap is on.

    Just got the 70mm lens, this is superb as a portrait lens.

    Chris

  22. #22
    Senior Member m3photo's Avatar
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    Re: Pentax 110 lens adapter for the G1

    Quote Originally Posted by ChrisJ View Post
    ... I would really like a spring loaded positive lock implemented, thinking cap is on.
    Just got the 70mm lens, this is superb as a portrait lens.
    I sorted that bit out by buying a 110 body for parts, cost me more for the postage! The thing is I never got past sticking the lens attachment mechanism on a spare c-mount adapter with black electrical tape to see if I liked the results from the lenses. Yes the 70mm is very good, shame about being stuck at f/2.8 though until I can get hold of something akin to your setup.

  23. #23
    Senior Member m3photo's Avatar
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    Re: Jinfinance

    OK, I've been pestering Rong Jin to make one for a few months now and finally he's come up with one. Not the diaphragm variety however but at least it's seventy dollars less than the other one on eBay!

    Here for all:

    http://cgi.ebay.com/ws/eBayISAPI.dll...ht_3928wt_1167

  24. #24
    Senior Member m3photo's Avatar
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    Sorry

    Oops, sorry folks - already mentioned here:

    http://www.forums.getdpi.com/forum/s...038#post178038

    Can't leave you lot for more than a day, can I?

  25. #25
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    Re: Sorry

    Quote Originally Posted by m3photo View Post
    Oops, sorry folks - already mentioned here:

    http://www.forums.getdpi.com/forum/s...038#post178038

    Can't leave you lot for more than a day, can I?
    Nope. just ordered one, and a few lenses from KEH. BTW, they have a 70mm f/2.8 left for under $50.

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