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Thread: Fresnell lens

  1. #1

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    Fresnell lens

    A few weeks ago i had a sad accident with my old anf faithfull Toyo, that served me well for over 15 years. It topled down from a small hill and landed sideways on a stone. Tripod and lens were unharmed, camera total loss: dented and bend house, front standard had broken off and the viewing screen had shattered into pieces...
    Luckely for me i had a good insurance on the camera and for the money i got back i decided to buy a ShenHao HZX45 II-A. I have been working with this new ca,eraa couple of times now and it handles so much easier then the old Toyo. Especially I am very pleased with the viewing screen: so much easier to focus. It realy snaps in, where the old Toyo always seemed to be a bit blurry. You had to focus very carefully to put the plane of focus where you wanted it.

    As to further improve the ease of focussing with the ShenHao i bought myself an additional fresnell lens. As this fresnell lens came without a manual it leaves me with the question on how to put in the camera: should the smooth side be towards the viewing screen or towards the lens panel side of the camera? Both options seem to be possible.

    I hope the fresnell lens will improve the brightness of the viewing screen when using wide angles, as is stated generally. But are there also disadvantages to using it, except for the few grams it will add to the weight of the camera? And if so: why hasn't every camera such a fresnell lens as a standard?

  2. #2
    AgX
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    In general:
    The orientation does not matter. As long as the fresnel lens is positioned back of the groundglas, at the photographer's side.
    For protecting the lens surface mounting the plain side of the fresnel lens towards the photographer is advisable.


    EDIT:
    should the smooth side be towards the viewing screen or towards the lens panel side of the camera? Both options seem to be possible.
    That would mean you you are considering installing the fresnel in front of the lerns.
    In general: No.
    Unless the camera is designed this way.


    In case there are rebates or such at a fresnel, the proprietory mounting should be used as different mounting could change position of the ground surface of the ground glass too.


    Basically the focal lenght of the fresnel lens must be chosen with the focal lenght or rather the exit angle of the taking lens in mind. But to my knowledge this ist not done in LF photography.
    Last edited by AgX; 04-17-2013 at 10:45 AM. Click to view previous post history.

  3. #3

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    Remove ground glass, by unscrewing two metal holders. Install Fresnel lens first, with grounded side looking toward you, put ground glass on the top of the Fresnel exactly same way as it was before, screw back metal holders. The Shen-Hao has a special spot for the Fresnel lens. You will see how the Fresnel will fit in its place after the ground glass removed.

  4. #4

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    Quote Originally Posted by Rudolf Karachun View Post
    Remove ground glass, by unscrewing two metal holders. Install Fresnel lens first, with grounded side looking toward you, put ground glass on the top of the Fresnel exactly same way as it was before, screw back metal holders. The Shen-Hao has a special spot for the Fresnel lens. You will see how the Fresnel will fit in its place after the ground glass removed.
    NO NO NO!

    If you follow these directions the ground glass will be out of register with the film plane. When adding a fresnel to a back that didn't come with one, the fresnel must go between the ground glass and the photographer.

  5. #5
    bobwysiwyg's Avatar
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    Quote Originally Posted by Dan Fromm View Post
    NO NO NO!

    If you follow these directions the ground glass will be out of register with the film plane. When adding a fresnel to a back that didn't come with one, the fresnel must go between the ground glass and the photographer.
    Now I'm confused. Per the ViewCameraStore in reference to the Shen Hao Fresnel they sell for the 4x5..

    "Easy to install.

    The screen drops in under the ground glass."

    WYSIWYG - At least that's my goal.

    Portfolio-http://apug.org/forums/portfolios.php?u=25518

  6. #6
    AgX
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    A lens placed in front of the ground glass will move the focal plane.
    In case this is taken care of with reference to the position of the film plane, thus in the construction of the camera, that should work.

  7. #7
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    Quote Originally Posted by AgX View Post
    A lens placed in front of the ground glass will move the focal plane.
    In case this is taken care of with reference to the position of the film plane, thus in the construction of the camera, that should work.
    Could you elaborate? I'm having a dense day. It would seem you can't have it both ways. If placed between the GG and the lens it moves the GG back some no matter what??
    WYSIWYG - At least that's my goal.

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  8. #8

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    You can't have it both ways. Either the focus panel/system was designed to have the fresnel in front of the GG or not.

  9. #9
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    Brian, pretty much what I thought. This suggests the ViewCameraStore instructions are incorrect? and the Fresnel should be mounted between the GG and the photographer's eye?
    WYSIWYG - At least that's my goal.

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  10. #10

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    I'd stop right now and dial the phone (if ViewCamera Store has a phone number) if I were you. What you read on ViewCamera store can be read etiehr way. If the focus panel was designed with a recess for fresnel under the GG then it seems like Rudolf could be right. If not, then Dan could be right.

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