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Thread: Fresnell lens

  1. #21

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    Thanks everyone for the reactions.

    Rudolf is right about how my ShenHao is constructed: the back has a provision for putting in a fresnell before the ground glass, without changing the register of the ground glass. The fresnel I bought seem to fit perfectly before the ground glas of the camera when checked with a caliper. What i wanted to ask is how I should position the fresnel: with the plain side towards the ground glass or towards the lens?

    My second question is what the disadvantage are of using a fresnel lens: some people seem to find it harder to focus the lens. Are there any other disadvantage sin using the fresnel i should aware of?

  2. #22

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    Thanks everyone for the reactions.

    Rudolf is right about how my ShenHao is constructed: the back has a provision for putting in a fresnell before the ground glass, without changing the register of the ground glass. The fresnel I bought seem to fit perfectly before the ground glas of the camera when checked with a caliper. What i wanted to ask is how I should position the fresnel: with the plain side towards the ground glass or towards the lens?

    My second question is what the disadvantage are of using a fresnel lens: some people seem to find it harder to focus the lens. Are there any other disadvantage sin using the fresnel i should aware of?

  3. #23

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    Fresnel concentric surface shall face the ground glass. Fresnel will help you to see things more brighter. I dont see any disadvantages in using it. May be some other do, but not me.

  4. #24
    shutterfinger's Avatar
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    Grooved side of the fresnel should face the ground glass.
    A fresnel eliminates hot spots and opens up the shadows making the overall scene lower contrast than it really is.
    The rings of the fresnel can make seeing the fine detail of a scene harder to see when using a loupe on the ground glass depending on how fine the rings are on the fresnel and how well you can "see".

    I had a Meridian 45B. I bought a reading fresnel from Office Max. I cut the fresnel down to fit the ground glass opening of the camera. Upon removing the ground glass I discovered the fresnel would fit between the frame and bosses for the ground glass without moving the ground glass position. After modifying the edges and assembling I checked the focus with a loupe from infinity to a few feet and no shift in focus.

  5. #25
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    I installed a fresnel in my old Shen Hao HZX-45AT-II. It was a Canham Fresnel/GG combo, purchased IIRC from The View Camera Store. I put the fresnel in front of the ground glass, and never had a problem with focus being off.

  6. #26
    LJH
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    Both of my Shen Hao's have a recess on the front side for a Fresnel so as to keep the GG in its original location.

  7. #27

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    By the way, dear friends. This is a nice and short article with pictures, about the Fresnel lens, how it is made and work.

    http://en.wikipedia.org/wiki/Fresnel_lens

    Please read it and try to explain me how it works, when the lens installed after the ground glass (mean between the ground glass and photographer) and with grooved surface of the Fresnel facing the ground glass.

    In my opinion it is understandable how the Fresnel works when installed before the ground glass (mean between lens and ground glass) and with grooved surface facing the ground glass. It just sending a parallel ray of light thru the ground glass. We all know that the ground glass by itself a diffuser. So with the Fresnel before, it seems like less light will be diffused by the ground glass, and image what photographer see on the surface of the ground glass will be much brighter then without the Fresnel.

    But what the Fresnel really do when located after the ground glass with grooved surface facing the ground glass?
    Thank you.

  8. #28
    AgX
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    The fresnel as any lens is of NO effect on the dispersion of the ground glass. This a fixed characteristic of the groundglass.
    A lens hower is of influence on the overall exit angle of the complete groundglass.

    The brightness of a groundglass can't be influenced by any lens. A lens though will influence the brightness-spread when viewed under a given viewing angle with respect to the groundglass.
    Last edited by AgX; 04-18-2013 at 12:15 PM. Click to view previous post history.

  9. #29

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    I was trying to understand something, but sorry, didnt.

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