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Lens Modifying
  • producerproducer

    I've read and watched all the available info about modifying the lens Pentax/Cosmicar/Rainbow 8-48mm f1.0.

    I just received Canon TV C-Mount Lens 8-48mm f1.0 which looks like Rainbow model:

    http://www.pentaxforums.com/forums/pentax-q/210138-adapting-rainbow-h6x8-ii-8-48mm-f1-0-cctv.html

    But the guides of modifying show difference between Rainbow and Canon at the thread construction inside.

    Please anyone who has CANON 8-48mm f1.0 for help about the right modifying!!!

    Big thanks in advance!

  • 50 Replies sorted by
  • balazerbalazer

    The screw has threads and is hollow. The shaft is solid and smooth.

  • patvigpatvig

    Thanks. But I have a diffulty to understand "shaft" (I'm French, novbvody is perfect!). When I look at the scews, one has metal aspect, the other one is black, thinner and shorter. This one is on the left when I put the camera body near me and the lens opposite regarding me. It is also a bit nearer of the camera lens. So, wich is shat?

  • balazerbalazer

    The screw locks the back focus. The shaft adjusts the back focus. Loosen the screw and then tighten it so it's just barely holding the back focus.

    Zoom to the maximum focal length and focus on something. Zoom to the minimum focal length and adjust the back focus until the item is in focus. Zoom to the max and adjust the focus again. Zoom to the minimum and adjust the back focus again. Repeat a third or fourth time if you want. At that point the back focus is adjusted. Tighten the locking screw.

    On this lens the back focus can't be set in a way that makes the lens parfocal for all focal lengths and focus distances. You need to pick the ones that matter to you and adjust the back focus for that situation.

  • patvigpatvig

    Can anyone explain how to adjust the focus with the 2 screws that appear in the focus adjust window?

  • nomadnomad

    Sure. Something like this:

    Tevidon_Abdrehen.png
    2090 x 1206 - 558K
  • fatpigfatpig

    I guess a lathe is the only way? since the back must stay exactly flat.

  • nomadnomad

    It will have to sink into the mount, so you may need to machine the rear of the lens down.

  • fatpigfatpig

    has anyone tried this adapter for a c-mount lens with a large diameter? http://www.ebay.de/itm/M42-C-Mount-Movie-Lens-to-Micro-4-3-M43-Mount-Adapter-Dual-Purpose-M42-C-M43-/371363295257?pt=LH_DefaultDomain_0&hash=item5676fa3019 my 12.5mm f1.4 Cosina is 41mm in diameter and this adapter could just do the trick.

    EDIT: If I hold the lens flush against the BMPCC, it still wont focus to infinity. I guess some modification is necessary. Any advice?

  • radikalfilmradikalfilm

    @producer, others: Please link to the 1mm thin flange Cmount/m43 adapter, I've tried a couple and they didn't work. Thank you,

  • nomadnomad

    Yep, same here. I have two Canon TV primes that resolve HD quite nicely if stopped down a bit.

  • fosterchenfosterchen

    Second that, @balazer.

  • balazerbalazer

    It's pointless using CCTV glass if you are using HD sensors.

    Not true at all. It depends on the individual lens. I have old TV lenses that are well above HD standards.

  • kazuokazuo

    It's pointless using CCTV glass if you are using HD sensors. These are lenses built for SD/analogue, and can't resolve at HD resolution. Inevitably, you will end up with v soft images, unless thats the look you want.

  • producerproducer

    Honestly, you don't need this lens at all. I modified it easily and 2 weeks later I sold it.

  • riclandricland

    What's the verdict?

    Should I buy this lens or my Gh2, and if I do, how do I go about modifying it? Also -- where do I buy it?

  • balazerbalazer

    The hood is plastic and it unscrews.

  • producerproducer

    After many other engagements finally I modified my Canon TV 8-48mm 1.0 lens successfully and attached it to GH2 with thinner adapter.

    But still there are vignettes on the angles of the image and I discovered that the reason is the hood of the lens which changes the vignetting when rotates during focusing.

    Is there a way to remove the hood, is it detachable at all? I tried by my hands without success.

  • producerproducer

    Is there any difference between Canon TV Zoom Lens 8-48mm and Computar TV Zoom Lens 8-48mm, except f1.2?

    http://liken.cc/UploadFiles/2012119143252466.jpg

  • producerproducer

    Well, the promised snapshots - ETC OFF and ETC ON. Video Mode. Lens held by hand!

    Again: the back black 6-screw part of the lens almost touches the GH2's flange, or just less than a milimeter distance for best focusing.

    00025.MTS_20130329_112935.181.jpg
    1024 x 576 - 34K
    00024.MTS_20130329_112834.997.jpg
    1024 x 576 - 73K
  • producerproducer

    Ok, tomorrow I will do that. The actual image circle without ETC doesn't even "touches" the upper and lower borders of the LCD screen.

  • balazerbalazer

    To check your lens's coverage, take a photo with ETC turned off and compare it to this. (GH2 4:3 large, 4608 x 3456; 8 mm f/2.8)

    But mostly I wouldn't worry about it at this stage. It's very hard to judge most aspects of a lens's performance before it's properly mounted and adjusted.

    Rainbow-H6x8-II-coverage.jpg
    4608 x 3456 - 279K
  • producerproducer

    Yes, it's 24p 1080, Creative Mode as well. Very, very weird!!!

  • balazerbalazer

    Make sure you have the mode dial set to Creative Movie, and you've selected a 1080 video mode in the menu (HBR, 24p, VMM, or 1080i). ETC mode has different effects depending on what photo or video mode you're in.

  • producerproducer

    Yes, there must be a distance up to 1mm, but the general problem is the vignetting which disappears after zooming-in almost half. Weird...

  • balazerbalazer

    Putting the lens flat against the GH2's flange is probably making them too close to each other, preventing proper focus and making the image circle a little too small. They should be about 1 mm apart - the thickness of the C-mount adapter. Until you have the right C-mount adapter, experiment by holding the lens different distances from the GH2 until you get focus.

    And make sure your ETC mode is working. Try turning ETC off. The difference should be obvious: with ETC mode off and the lens zoomed out, this lens projects a circle that covers only about a quarter of the GH2's sensor, with lots of black all around.

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