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Thread: You know what we need?

  1. #1
    Senior Member RichA's Avatar
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    You know what we need?

    A machining service to deal with these lenses. The shot below was taken with a Cosmicar (Pentax) 12.5mm f1.4 1" CCTV lens on a Panasonic G1. That is as far as I can get with that lens from an object right now. The Cosmicars are exceptionally good. Not inferior to the Schneiders and the Angenieux lenses in any way, and you can still buy them at affordable prices. But, the 12.5mm has a very slightly too wide back that won't fit into the recess of the 4/3rds to c-mount adapter. So, about 1mm needs to be taken off for it to fit. We're talking about 10 minutes for a machinist and a small lathe. A service like that, even one to make a new rear retaining cap to replace the original for these kinds of lenses would be good, and the costs would be low, maybe $40-$50 for basic jobs like that.


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    Senior Member kds315's Avatar
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    Re: You know what we need?

    ...but unfortunately you seem to forget that the poor machinist might not be willing to take the risk of mounting the lens to his lathe, since it might damage it...had that discussion already...

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    Re: You know what we need?

    Quote Originally Posted by kds315 View Post
    ...but unfortunately you seem to forget that the poor machinist might not be willing to take the risk of mounting the lens to his lathe, since it might damage it...had that discussion already...
    The brass base comes off the Cosmicar 12.5mm f/1.4 with three grub screws in a half a moment. Very easy to chuck in a lathe and turn. Only problem is that to fit it to the C-mount adapter, it needs to be relieved about a third of the way up the grub screw threads so you might need to run a tap through them to refit the base to the lens, but it's not hard at all to work with. There's plenty of meat for the grub screws to be re-fitted and hold the lens body securely.

    I'm no machinist, but I did mine in about 10 minutes on a borrowed lathe.

  4. #4
    Senior Member RichA's Avatar
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    Smile Re: You know what we need?

    Quote Originally Posted by kds315 View Post
    ...but unfortunately you seem to forget that the poor machinist might not be willing to take the risk of mounting the lens to his lathe, since it might damage it...had that discussion already...
    Any machinist who would chuck the whole lens has a screw loose.

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    Re: You know what we need?

    You know what we need?

    Just a small (cheap) key file and ~30mins of filing for each flange. It is important to note that even rough finishes will not affect the planarity of the flange (where it meets the adapter) since only the sides are trimmed and the cosmetics will not not show when the lens is mounted on an adapter.

    Some of us do not need a machinist for jobs like this.

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    Re: You know what we need?

    This service did exist at one time on this forum. I had a Comiscar 12.5/1.4 and Tevidon 25/1.4 modded back then.

    But I agree with Vivek. I modded two of my c-mounts so I could obtain infinity focus. Wasn't the prettiest mod, but the results were fine.

  7. #7
    Senior Member RichA's Avatar
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    Re: You know what we need?

    Quote Originally Posted by wjlapier View Post
    This service did exist at one time on this forum. I had a Comiscar 12.5/1.4 and Tevidon 25/1.4 modded back then.

    But I agree with Vivek. I modded two of my c-mounts so I could obtain infinity focus. Wasn't the prettiest mod, but the results were fine.
    I'm still debating doing it with the Cosmicar 12.5mm. I've seen lathed mods and they actually show a clean ring of material removed, not a bevel, but an actual squared off reduction in rear barrel diameter sufficient to clear the adapter shoulder. I hope there is enough material to simply file a bevel.

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    Re: You know what we need?

    Quote Originally Posted by RichA View Post
    I'm still debating doing it with the Cosmicar 12.5mm. I've seen lathed mods and they actually show a clean ring of material removed, not a bevel, but an actual squared off reduction in rear barrel diameter sufficient to clear the adapter shoulder. I hope there is enough material to simply file a bevel.
    I wonder if someone who has tried the Vivek approach could post a picture of the result? I have a Cosmicar and I am very tempted to do this myself, with a file.

    Keith

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    Re: You know what we need?

    This is a Fujinon-TV 25/1.4 (example- gives an idea):





    An important lesson learnt from this:

    The file slips while filing. So mask all the areas that aren't going to be filed.

    I was able to inform Y.B. Hudson of this and he may have a cleaner looking end product.

  10. #10
    thearne3
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    Re: You know what we need?

    Here is another example. Pictured lenses are Computar 25mm and 12.5mm. I used a fine three sided file for about 30 minutes on each. Close to a clean notch. Careful not to go any farther toward center than necessary - I have an extra 12.5mm for parts because I filed off too much and the base broke off! Also, as Vivek noted: mask the areas not being filed - both for cosmetic reasons and to avoid fine filings in the moving parts of the lens. I use black electrical tape.

    Best,
    Tom


  11. #11
    Member slosync's Avatar
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    Filed Cosmicar

    Here is a Cosmicar I filed at home. Note how far up the flange you have to go to have it fit into the adapter... I tried to keep the file at approximately a 45 degree angle while filing. If you note Tom's picture above you can see you don't have to go past the set screws if you have it machined.

    Cheers,
    Don


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    Re: You know what we need?

    Thanks everyone for these pictures, I'm starting tomorrow!

    Keith

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    Senior Member RichA's Avatar
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    Re: You know what we need?

    Quote Originally Posted by thearne3 View Post
    Here is another example. Pictured lenses are Computar 25mm and 12.5mm. I used a fine three sided file for about 30 minutes on each. Close to a clean notch. Careful not to go any farther toward center than necessary - I have an extra 12.5mm for parts because I filed off too much and the base broke off! Also, as Vivek noted: mask the areas not being filed - both for cosmetic reasons and to avoid fine filings in the moving parts of the lens. I use black electrical tape.

    Best,
    Tom

    If I could file like that, I'd be a human lathe!

  14. #14
    Senior Member RichA's Avatar
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    Re: You know what we need?

    BTW, the Fuji 25mm f1.4 in the picture was easy because it had a retaining ring that I could remove (not a base with integrated c-mount like the Cosmicars). I replaced it with the sliced off top of a black film container. I wish they were all that easy.

  15. #15
    Senior Member ecsh's Avatar
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    Re: You know what we need?

    If someone has a seriously screwed up lens they want me to try and get better, i use both a lathe and mill at home. PM me if your interested, as i would like to see what can be done to make this look better than some of the examples above, LOL.
    Joe

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    Member LizaWitz's Avatar
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    Re: You know what we need?

    Wouldn't it be better to make the well of the C-mount adapter a bit wider, rather than to modify every lens?

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    Re: You know what we need?

    Quote Originally Posted by ecsh View Post
    If someone has a seriously screwed up lens they want me to try and get better, i use both a lathe and mill at home. PM me if your interested, as i would like to see what can be done to make this look better than some of the examples above, LOL.
    Joe
    Sample from that Fujinon-TV 25/1.4 (f/1.4)



    Try making something that.

    Quote Originally Posted by RichA View Post
    BTW, the Fuji 25mm f1.4 in the picture was easy because it had a retaining ring that I could remove (not a base with integrated c-mount like the Cosmicars). I replaced it with the sliced off top of a black film container. I wish they were all that easy.

    I found that out later. Anyway, the Fujinon is harder because it is a tough aluminium alloy as opposed to the soft Cosmicar/Computar brass flanges.

  18. #18
    thearne3
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    Re: You know what we need?

    Quote Originally Posted by LizaWitz View Post
    Wouldn't it be better to make the well of the C-mount adapter a bit wider, rather than to modify every lens?
    Liza,

    I can only speak for the RJ Camera adapter - doesn't appear to have enough material. But perhaps you were referring to a change in the manufacturing spec? ...that would be the best option! I can see no reason why the Far East sources could no modify the adapter to accommodate the wider shoulder of many lenses. I wonder if we could develop a consensus spec and 'campaign' (email the various sources) for it? Hard to imagine this has not already been done...

    Best,
    Tom

  19. #19
    carsonc
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    Re: You know what we need?

    share my experience too

  20. #20
    Senior Member Y.B.Hudson III's Avatar
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    Re: You know what we need?

    how did I miss this thread?



    fuji 25mm...
    Last edited by Y.B.Hudson III; 27th February 2010 at 01:01. Reason: spelling

  21. #21
    Member JimBuchanan's Avatar
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    Re: You know what we need?

    Could someone enlighten me as to where to find these type lenses? Do the cine lenses offer image quality over the typical, say CV M lenses, for video or stills? And which format will cover the m4/3 frame? I've heard the "C" lenses have too small image circle.

    I would like to take an example or 2 of the most popular ones and lathe fit it to a common adapter to see whats involved.

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    Re: You know what we need?

    Quote Originally Posted by JimBuchanan View Post
    Could someone enlighten me as to where to find these type lenses? Do the cine lenses offer image quality over the typical, say CV M lenses, for video or stills? And which format will cover the m4/3 frame? I've heard the "C" lenses have too small image circle.
    These are lenses primarily used in industrial applications for machine vision, or for CCTV. There are quite a few manufacturers and suppliers out there for these. For the most part you want 1" lenses. Here's a link to some C-mount lens coverage: C-mount compatibility

    Quote Originally Posted by JimBuchanan View Post
    I would like to take an example or 2 of the most popular ones and lathe fit it to a common adapter to see whats involved.
    The issue with that is each lens is pretty much different in terms of their mount. I have a Cosmicar 12.5 and a Computar 12.5, and they have different machining requirements. On the other hand, there are a number of different C-mount adapters available for m4/3, each with their own clearances and machining requirements. I'm using a Kipon adapter, which is lower profile thus allowing me to machine less off the lens mount. Other adapters require more machining.

    Short answer: there's a LOT of different combinations of lens mounts and available adapters, so it'll have to be a custom job for each lens.

    I'm looking to buy a small hobby lathe to try and machine my mounts (and for other hobby stuff), but it'll be a while before I actually make the purchase to try it (gave up buying photo gear for Lent...).

  23. #23
    Member JimBuchanan's Avatar
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    Re: You know what we need?

    Thank You, for the C-mount reference.

    I'm still trying to understand what the deal is on cine lenses with m4/3 with the high prices and all. Does a cine lens take better video than a still photography lens?

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    Re: You know what we need?

    Quote Originally Posted by JimBuchanan View Post
    Thank You, for the C-mount reference.

    I'm still trying to understand what the deal is on cine lenses with m4/3 with the high prices and all. Does a cine lens take better video than a still photography lens?
    The meaning of 'better' in photography and video is definitely in the eye of the beholder. To be sure, older lenses (cine or otherwise) have their own special character, which gives pictures or video a different look than today's ultra-sharp lenses. That drives the pricing, as does the collectible and rare nature of some of these lenses, many of which are more than 50 years old.

  25. #25
    maxmorrison
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    Re: You know what we need?

    Just get a Cosmicar 12.5 f1.4. Tomorrow filing time ^_*
    Hopefully I will post photo about the whole process and the modded lens.

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    Re: You know what we need?

    Quote Originally Posted by maxmorrison View Post
    Just get a Cosmicar 12.5 f1.4. Tomorrow filing time ^_*
    Hopefully I will post photo about the whole process and the modded lens.

    Look forward to seeing that - I'm half way through, it just needs a lot of patience

    Keith

  27. #27
    maxmorrison
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    Re: You know what we need?

    Quote Originally Posted by woodmancy View Post
    Look forward to seeing that - I'm half way through, it just needs a lot of patience

    Keith
    Yes a LOT of patience...
    Took one hour to file hard and another hour trying to fine tune the job.
    But is worth the pain, I finally got the infinity focus

    Here some pics, have a good Sunday (here is Snowing...)

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    Re: You know what we need?

    Quote Originally Posted by maxmorrison View Post
    Yes a LOT of patience...
    Took one hour to file hard and another hour trying to fine tune the job.
    But is worth the pain, I finally got the infinity focus

    Here some pics, have a good Sunday (here is Snowing...)
    Well done, Max

    Keith

  29. #29
    maxmorrison
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    Re: You know what we need?

    First try with the Cosmicar 12.5


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