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Thread: hacking a lens to fit a C mount

  1. #1
    Senior Member pellicle's Avatar
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    hacking a lens to fit a C mount

    Hi

    I did a hack on a Computar lens to get it to fit an adaptor. I know at least Godfrey is interested to see what i did to the lens (it wasn't major)

    http://cjeastwd.blogspot.com/2009/06...fit-mount.html

    I guess that this image will say it all for him :-)



    now, off to take some pictures with it (rather than of it)

    :-)

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    Re: hacking a lens to fit a C mount

    Wow that's just what I was asking folks here about in terms of how to get lenses to fit better in the c-mount adapter. Is there anything you need to be aware about when you grind that edge? I have a Dremel with a grinder you think that will do it to smooth it out. I also don't want to ruin my tv lens granted it wasn't that expensive.

    Thanks for that post and info.!

  3. #3
    Member slosync's Avatar
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    Re: hacking a lens to fit a C mount

    Thanks for that picture and your excellent description on your blog for modifying the Comutar Lens. I have the similar issue with a 25mm 1.4 Cosmicar, but perhaps a little more filing may be necessary.

    As soon as I receive my Hawk C adapter, I will make the modification. I have the little C Pentax 25mm 1.4, I'm hoping the Cosmicar lens may a little sharper. Here's a picture of my Grandaughter using the Pentax.

    Pentax TV C lens 25mm f/1.4 at 1.4 - Grandaughter

    Cheers,
    Don

    Quote Originally Posted by pellicle View Post
    Hi

    I did a hack on a Computar lens to get it to fit an adaptor.

    http://cjeastwd.blogspot.com/2009/06...fit-mount.html





    :-)
    Last edited by slosync; 12th June 2009 at 06:50.

  4. #4
    Senior Member pellicle's Avatar
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    Re: hacking a lens to fit a C mount

    Hi

    Quote Originally Posted by gmoe View Post
    Wow that's just what I was asking folks here about in
    thanks, a bit of positive feedback goes miles :-)

    terms of how to get lenses to fit better in the c-mount adapter. Is there anything you need to be aware about when you grind that edge? I have a Dremel with a grinder you think that will do it to smooth it out.
    actually a Dremel (well controled) would be prefect .. I found myself wishing for mine (which is back in Australia). I understand there is quite an amount on there to shave off, but I just took it carefully and slowly trying it from time to time.

    I also turned the lens around and screwed it in from the back to see how much I should be expecting to come through too.

    HTH

  5. #5
    Senior Member kweide's Avatar
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    Re: hacking a lens to fit a C mount

    One pass on a turning lathe......just some seconds work...
    Less than 5 Minutes with a Dremel
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  6. #6
    Senior Member pellicle's Avatar
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    Re: hacking a lens to fit a C mount

    Hi

    some examples from today:





    The lens seems to have quite some curvature of filed as the distance around the edges happened to be in focus when the foreground center was.

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    Super Duper
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    Re: hacking a lens to fit a C mount

    thank you! I've ordered one of Hawk's adapters ... eh? you can't take it with you ... ;-) ... as it looks like I can hack the Cosmicar 12.5mm similarly. Might as well have some fun with it.

  8. #8
    Super Duper
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    Re: hacking a lens to fit a C mount

    Hack away, gentlemen.


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    Re: hacking a lens to fit a C mount

    Quote Originally Posted by monza View Post
    Hack away, gentlemen.

    Is the rightmost lens in this set the Cosmicar 12.5/1.4? If so, that's a good guide to what I need to do for Hawk's adapter. :-)

  10. #10
    Super Duper
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    Re: hacking a lens to fit a C mount

    Yes.

  11. #11
    Senior Member pellicle's Avatar
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    Re: hacking a lens to fit a C mount

    Hi monza

    these look like they've been turned down to suite the RJ mount ... no?

  12. #12
    Super Duper
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    Re: hacking a lens to fit a C mount

    Actually they were machined to fit the Hawk but should work on any c-mount adapter. I added shims (in the form of metallic tape) to fine tune infinity...

  13. #13
    Senior Member pellicle's Avatar
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    Re: hacking a lens to fit a C mount

    Hi

    what's the stumpy one second from the right?

  14. #14
    Super Duper
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    Re: hacking a lens to fit a C mount

    Carl Zeiss DDR Tevidon 25/1.4

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    Senior Member m3photo's Avatar
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    Taken with a Carl Zeiss DDR Tevidon 25/1.4

    G1 - 16:9 format 1/25th f5.6 800 ISO hand-held (elbows firmly on the table).

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    Re: Taken with a Carl Zeiss DDR Tevidon 25/1.4

    Quote Originally Posted by m3photo View Post
    G1 - 16:9 format 1/25th f5.6 800 ISO hand-held (elbows firmly on the table).
    Very nice. Surely a lot more compact than the Summilux 25mm f/1.4 I've been using ... :-)

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    Re: hacking a lens to fit a C mount

    Had some entertaining difficulties making the Cosmicar 12.5mm fit, but it's working fine now.


    Panasonic G1 + Cosmicar 12.5mm f/1.4
    ISO 100 @ f/4 @ 1/320 sec
    flickr page: http://www.flickr.com/photos/gdgphoto/3658294863/

    enjoy

  18. #18
    Ranger 9
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    Re: hacking a lens to fit a C mount

    Godfrey - looks good, although there seems to be a surprising lack of DOF for f/4... the bubbles in the espresso are sharp, but the spoon and truffles look to be OOF a bit.

    Also, the vignetting along the edges of your shot looks quite straight-edged; I've got the 12.5/1.9 Cosmicar (the older, skinnier one) and its edge-falloff pattern is noticeably round.

    -- Is the f/1.4 version "squarer"?

    -- Or did you vignette the edges in post to blend in with the natural falloff in the corners? If so -- good trick! I'll have to try that myself.

  19. #19
    patbon23
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    Re: hacking a lens to fit a C mount

    I am Italian and not speak English very well,
    how can I solve the problem of focus to infinity with a tevidon 25mm?
    thanks

  20. #20
    Senior Member m3photo's Avatar
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    Re: Focus to infinity with a tevidon 25mm

    Quote Originally Posted by patbon23 View Post
    I am Italian and not speak English very well,
    how can I solve the problem of focus to infinity with a tevidon 25mm?
    thanks
    Hello,
    On this page go to message number 8 - in the picture you will see 4 lenses, yours is the smallest one. If you don't have a lathe, print the picture and take it with you together with the lens and the adapter to a machine shop and explain that you need this part grinding down so it fits better in the adapter - this is why you aren't able to get infinity focus with the lens as it is.

    I don't speak Italian, maybe you can understand some Spanish:

    Hola,
    En esta página sube hasta el mensaje número 8 - en la foto verás 4 objetivos, el tuyo es el más pequeño. Si no tienes torno, imprime la foto y llévatela junto con el objetivo y el adaptador a un tornero y explícale que necesitas rebajar esta parte para que encaje mejor en el adaptador - esta es la razón por la cual no consigues enfocar al infinito con el objetivo como está.

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    Re: hacking a lens to fit a C mount

    Quote Originally Posted by Ranger 9 View Post
    Godfrey - looks good, although there seems to be a surprising lack of DOF for f/4... the bubbles in the espresso are sharp, but the spoon and truffles look to be OOF a bit.

    Also, the vignetting along the edges of your shot looks quite straight-edged; I've got the 12.5/1.9 Cosmicar (the older, skinnier one) and its edge-falloff pattern is noticeably round.

    -- Is the f/1.4 version "squarer"?

    -- Or did you vignette the edges in post to blend in with the natural falloff in the corners? If so -- good trick! I'll have to try that myself.
    Thanks for looking and commenting!

    DOFmaster calculates that a 12.5mm lens on FourThirds format, focused to 9 inches and set to f/4, will render a total DoF of 1.5 inches. That seems about right, looking at this photo! ;-)

    Yes, I add vignetting on these square compositions to blend in the hard corner vignettes a little more smoothly. I think it gives them a unique feel. The natural falloff to the edges of the lens coverage is another interesting adjustment this lens can make: at f/1.4, it has a natural center to edge falloff of about 1.5EV, at f/5.6 the falloff has disappeared, so there is a lot of different qualities to work with when I'm shooting and rendering.

  22. #22
    daggerlee
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    Re: hacking a lens to fit a C mount

    Thanks for the great work pellicle!

    I'm about to order a C-mount adapter from hawkpeng, but which one should I get? The "C5 type TV Bolex C Mount" or the "Bolex W1 C"? Apparently the second one can be used with Pen F and Robot lenses, with care. Both listings use the same pictures, but the second one is more expensive. Thanks!

  23. #23
    Super Duper
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    Re: hacking a lens to fit a C mount

    They are identical except the second one has set screws so it can work the Hawk's Pen F flange, an original Pen F Extension tube flange, or Hawk's Robot flange.

  24. #24
    daggerlee
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    Re: hacking a lens to fit a C mount

    Thanks for the info monza, have ordered one of the basic ones. Thought about getting the one that can work with Pen F flange but am hoping that someone will soon put out a dedicated Pen F to M43...

  25. #25
    Super Duper
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    Re: hacking a lens to fit a C mount

    The Hawk adapter in combination with the Pen F flange, is essentially a dedicated adapter. Jinfinance also has a dedicated adapter.

  26. #26
    patbon23
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    Re: Focus to infinity with a tevidon 25mm

    Quote Originally Posted by m3photo View Post
    Hello,
    On this page go to message number 8 - in the picture you will see 4 lenses, yours is the smallest one. If you don't have a lathe, print the picture and take it with you together with the lens and the adapter to a machine shop and explain that you need this part grinding down so it fits better in the adapter - this is why you aren't able to get infinity focus with the lens as it is.

    I don't speak Italian, maybe you can understand some Spanish:

    Hola,
    En esta página sube hasta el mensaje número 8 - en la foto verás 4 objetivos, el tuyo es el más pequeño. Si no tienes torno, imprime la foto y llévatela junto con el objetivo y el adaptador a un tornero y explícale que necesitas rebajar esta parte para que encaje mejor en el adaptador - esta es la razón por la cual no consigues enfocar al infinito con el objetivo como está.
    this is my C-mount lens, has been hacked but I can't however to use it at infinity

  27. #27
    Senior Member m3photo's Avatar
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    Re: Focus to infinity with a tevidon 25mm

    Quote Originally Posted by patbon23 View Post
    this is my C-mount lens, has been hacked but I can't however to use it at infinity
    Mine does - on a HawkPeng C-Mount Adapter. Maybe you should try some more grinding?

  28. #28
    patbon23
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    Re: hacking a lens to fit a C mount

    take with pentax 12.5mm at F11

  29. #29
    Senior Member RichA's Avatar
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    Re: hacking a lens to fit a C mount

    Quote Originally Posted by pellicle View Post
    Hi

    I did a hack on a Computar lens to get it to fit an adaptor. I know at least Godfrey is interested to see what i did to the lens (it wasn't major)

    http://cjeastwd.blogspot.com/2009/06...fit-mount.html

    I guess that this image will say it all for him :-)



    now, off to take some pictures with it (rather than of it)

    :-)
    A lot of modern larger sensor format CCTV lenses do not fit. Older lenses for "TV" and 16mm movie cameras do tend to fit the RJ adapter, but the TV lenses often lack coverage because of the size of sensors back when. Of these lenses:
    -12.5mm f1.4 Cosmicar needs modification and does not quite cover the field.
    -25mm f1.4 Fujinon needs modificaction but covers the entire field of the G1, with vignetting that is gone by f11.
    -6mm f1.2 Computar fits and its image circle = 1/3 of camera field
    -18mm el cheapo Cosmicar fixed f1.6 aperture fits, but image circle doesn't cover the whole field.
    -little Pentax 110 24mm needs adapting but does cover the field in the G1.
    The 12.5mm and 25mm lenses are 1" CCTV lenses, the others cover smaller formats.

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    Re: hacking a lens to fit a C mount

    Quote Originally Posted by pellicle View Post
    Hi

    I did a hack on a Computar lens to get it to fit an adaptor. I know at least Godfrey is interested to see what i did to the lens (it wasn't major)

    http://cjeastwd.blogspot.com/2009/06...fit-mount.html

    I guess that this image will say it all for him :-)



    now, off to take some pictures with it (rather than of it)

    :-)
    Hi, I am impressed by your work. Since I am not quite familiar with metalwork, may you post some pictures of your setup? I have some basic tools such as driller and a desktop polisher. I would like to know what kind of accessories I should have to trim it. Your demonstration really give me a more clear idea.

    Many thanks

  31. #31
    Senior Member pellicle's Avatar
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    Re: hacking a lens to fit a C mount

    Hi

    Quote Originally Posted by pentacon6 View Post
    Hi, I am impressed by your work. Since I am not quite familiar with metalwork, may you post some pictures of your setup?
    Many thanks
    well, ok ... but I think you might be disappointed ... its just a table and my leatherman (which has a file on it). Totally nothing fancy.


    as to my workmanship, heck I'm a bit shy about that, by metalwork standards its like the advice given by the cabinet maker to the carpenter

    paint it and no one will notice

  32. #32
    patbon23
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    Re: hacking a lens to fit a C mount

    After two hours of work , my cosmicar 12.5mm works , as soon as possible I'll send the pictures

  33. #33
    patbon23
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    Re: hacking a lens to fit a C mount

    this is my "new" Cosmicar 12.5

    Photo take F5.6 focus infinity

  34. #34
    thearne3
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    Unhappy Re: hacking a lens to fit a C mount

    Hi,

    Just received my Computar 12.5mm f1.3 and before I start grinding, I have a question: should it rattle? When I shake it in the same axis as the light would pass through (lengthwise), there is a distinct sound of something moving inside. The sound is minimized when the aperture is wide open.

    I have never had any lens behave this way. Is this unique to this model or a fault? The cosmetics of the lens 'like new'.

    Any advice?

    Thanks,
    Tom

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