No-name CCTV lens

Discussion in 'Adapted Lenses' started by Cerebus2, Jan 11, 2011.

  1. Cerebus2

    Cerebus2 Mu-43 Rookie

    Oct 12, 2010
    Having seen a number of shots with various 25/1.4 C-mount CCTV lenses out there, I just had to get one for myself. I simply love the aesthetic from these things; he corner fall-off, swirly bokeh, and sharp center combine for something I really enjoy.

    I picked up a no-name eBay special with m43 adapter. I haven't checked infinity focus (cloudy nights in the sticks don't give you much to test with) but it seems to me that it focuses waaaay past infinity, and close focus is ~4'. Is this typical or should I spring for a better C-mount adapter?

    At any rate the lens is certainly useable and I'm looking forward to playing with it; I'm just curious.

    -- C
  2. Kosta

    Kosta Mu-43 Veteran

    Sep 29, 2010
    pics or ban!

    only kidding! enjoy the new lens, they are definitely fun and can give some really surreal looking pictures!
  3. Cerebus2

    Cerebus2 Mu-43 Rookie

    Oct 12, 2010
    So I checked infinity focus this AM, and it is indeed waaaaay out of whack. To get proper infinity, I have to unthread the lens about 3/4 of the way out of the mount (leaving a good couple of mm of thread). This naturally makes the lens a bit wobbly and difficult to use.

    So the $6.40 question is, is this the wrong adapter, ill-made adapter, or is the lens designed for a different flangeback?

    Anyone with any modding experience have any suggestions?
  4. RetroBoy

    RetroBoy Mu-43 Regular

    Just chiming in to say I have the same problem with my Cosmicar 25 f/1.8 TV lens.

    It will only focus between about 200mm to 350mm distance.

    I did some searching but haven't seen an answer yet.
    Looking at my 2 other C mount lenses, the exit pupil is around 15mm (5/8")in from the mount for those but for this 25mm lens the exit pupil is right in line with the mount.

    So I'm thinking it may need a different adapter that places it further away from the sensor. Hopefully someone who knows will be able to answer...
  5. Cerebus2

    Cerebus2 Mu-43 Rookie

    Oct 12, 2010
    So the problem is that the C-mount standard has a lot of slop. Apparently it's generally expected that each C-mount lens should be collimated for each camera.

    Normally collimation should only be slightly out, usually allowing focus past infinity by a reasonable amount. In my case the lens appeared to have been assembled oddly, or was collimated for a camera with a odd flange back (no, it's not a CS mount, I checked). The rear element housing was actually hitting the baffles inside the sensor box.

    Fortunately collimation is pretty simple on this lens. I used one of my SLRs to make a target, loosened the focus ring set screw, and moved the ring to the other side of the focus stop before reseating the set screw. Now my lens is only slightly out of collimation; I can still go past infinity, but only by a small amount. Close focus is also about where you'd expect it. It'll be easier to correct the remaining problems with a shim on the mount threads, but I can do that later.

    I'll post a pic when I get a chance to offload the card.

    -- C
  6. iliakoltsov

    iliakoltsov Mu-43 Regular

    Aug 7, 2010
    Cerebus you can adapt the lens to the adapter, indeed this is a C mount but from CCTV larger diameter had the same problem with the 35 1.7.