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Thread: is there workaround for lenses that don't cover full sensor?

  1. #1
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    is there workaround for lenses that don't cover full sensor?

    Hi all,

    I just want to say thanks everyone in advance for all your expertise on the G1. This is my first post and I look forward to meeting and sharing knowledge with this great community.

    My interest is with the new GH1 and I'm excited about the possibility of using older c-mounted lenses for documentary film work. One of the challenges is finding lenses that will fit the entire sensor.

    For lenses that do not cover the whole sensor, for example using tv zoom lenses for 2/3 cameras, that only cover part of the sensor, would it be possible to add a closeup lens to remove some of the vignetting?

    Or is there a cropping feature on the G1 that may be also on the GH1 so that the image can go past the vignetting?

    Thanks in advance!

    -Gmoe

  2. #2
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    Re: is there workaround for lenses that don't cover full sensor?

    I don't see how a closeup lens would remove vignetting caused by inadequate coverage. You could stretch the coverage by extending the lens (via extension tubes, for example) which would increase the projection distance and allow the rays to expand farther before they strike the imager. But then you'd be limited to the macro range.

    A number of G1 users have posted here that many lenses that vignette noticeably when shooting in the 4:3 or 3:2 formats are less problematic when shooting in the 16:9 format. 16:9 uses the full width of the sensor but reduces the height, so the darkened corners are cropped off. The GH1 has a differently-proportioned sensor, so it remains to be seen how well this trick will work with it.

  3. #3
    milapse
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    Re: is there workaround for lenses that don't cover full sensor?

    Don't forget the G1/GH1 have a 2x zoom feature that works perfectly with smaller image circle lenses. From samples I've seen @2x in the video mode it looks quite good (insignificant loss in quality).

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    Re: is there workaround for lenses that don't cover full sensor?

    Thanks guys!

    Ranger 9

    You could stretch the coverage by extending the lens (via extension tubes, for example) which would increase the projection distance and allow the rays to expand farther before they strike the imager. But then you'd be limited to the macro range.
    How about a 5mm extension tube for a c-mount lens just to get a tad of the vignetting out of the way since I'll be shooting mainly in 16x9. Maybe something like this? They also have 10mm or 15mm. Never used an extension tube before which should I choose?

    http://www.bhphotovideo.com/bnh/cont...G&A=details&Q=


    milapse

    Quote Originally Posted by milapse View Post
    Don't forget the G1/GH1 have a 2x zoom feature that works perfectly with smaller image circle lenses. From samples I've seen @2x in the video mode it looks quite good (insignificant loss in quality).
    That's great news then milapse, so the extension tube could be my backup. With the 2x zoom feature is that both in 4:3, 3:2 and 16:9 mode? If the quality on the 2x zoom feature does not drop then that may be a nice workaround.

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    Re: is there workaround for lenses that don't cover full sensor?

    Quote Originally Posted by milapse View Post
    Don't forget the G1/GH1 have a 2x zoom feature that works perfectly with smaller image circle lenses. From samples I've seen @2x in the video mode it looks quite good (insignificant loss in quality).
    Milapse - how do you access that feature. I've tried and can't do it.

    Keith

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    Re: is there workaround for lenses that don't cover full sensor?

    You can't use that feature with picture size set to Large. You need to change it to Medium or Small. Then continue to the third page of the REC section where you changed the picture size and the first choice on top is EZ in a rectangle EX. OPT ZOOM--choose On. When you go back to picture size and choose Large you'll see that the feature isn't available, but it is with Medium or Small. Not sure how that is affected by shooting RAW, or in Auto Mode.

    I did try it with my Cosmicar 12.5/1.4 and the vignette did disappear, but the lens smears something horrible, so I put it on the shelf--too bad because this is one of the few superwides that is close to covering the sensor. Other lenses I tested were the Kodak 15/2.5, Schneider 10/1.9, and Kern 25/1.4 and it didn't remove the vignette completely of the first two, but did for the Kern, but the Kern was close to covering the sensor.

    Quote Originally Posted by woodmancy View Post
    Milapse - how do you access that feature. I've tried and can't do it.

    Keith

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    Re: is there workaround for lenses that don't cover full sensor?

    Quote Originally Posted by wjlapier View Post
    You can't use that feature with picture size set to Large. You need to change it to Medium or Small. Then continue to the third page of the REC section where you changed the picture size and the first choice on top is EZ in a rectangle EX. OPT ZOOM--choose On. When you go back to picture size and choose Large you'll see that the feature isn't available, but it is with Medium or Small. Not sure how that is affected by shooting RAW, or in Auto Mode.
    Wjlapier - thanks for this, I'll stick to cropping out the vignette, I think. I shoot raw all of the time at maximum size. The 16:9 aspect ration does help though.

    Keith

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