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Thread: Changing Linhof "Ground glass"

  1. #1

    Changing Linhof "Ground glass"

    Hello everyone,

    Two weeks a go, I bought a new ground glass "Beattie" for my linhof camera(nothing wrong with the old one just would like to upgread) I found that the original Linhof ground glass has only one sheet. It means one side is used as a matte surface to project the picture...OK?

    Now this a problem....

    "The Beattie" groung glass for Linhof comes with two sheets. First is mulitcode glass and 2rd is Arclic sheet which is one side is matte and fresnel screen another. I just put it following the instruction. I found something. My infinity focus was changed ( My Linhof has a lock infinity focus)... and now, I'm feel not so sure with foucsing

    They have a differance between one sheet ground glass and two sheets ground galss. The matte surface was changed the level ( up or down or diagonal). I really would like to draw to show my problem. It will be better than discrib by word.......

    "How can we sure when we focus on the ground glass that appeared the same focus (distant) with the film sheet (in film sheet holder)?..

    "What happen if ground glass is not in position?"

    I believe is just a litte bit problem with typical focus, but for infinity , It will be a main problem (non focusing)

    If any one know this problem please email to me. I can give you sketch of my problem ,so on , maybe we can talk by phone.

    Please.... Thank you . Ten

  2. #2

    Join Date
    Jan 2001
    Posts
    4,010

    Changing Linhof "Ground glass"

    Put the matt surface of your new screen in the same location as the matt surface of your old screen, relative to the lens. Be careful not to lose the tiny shims around the edges of the frame which holds the screen.
    Wilhelm (Sarasota)

  3. #3

    Changing Linhof "Ground glass"

    I assume you have a 45 Linhof.

    When you remove the old gg you will see that the frosted side lies on top of the 4 shims in the corners. You place the new gg on top of the shims (without making any changes to their position) with the frosted side down. You then replace the two hold-down strips for the gg. You then use the fresnel screen clips that should be on the center screw of the hold down strips to hold the fresnel screen in place. The fresnel should be positioned so the smooth side is towards your eye.

    If your camera does not have the Linhof fresnel clips and you are in the US you can buy them from Linhof service at 973 808-9010. They can also answer any more questions regarding changing your gg.

  4. #4

    Changing Linhof "Ground glass"

    Varkan: Never put the Fresnel on the side of the ground glass that looks to the lens. It will shift the focus. Follow Bob's advice, that should solve the problem.

  5. #5
    Mike Lewis
    Join Date
    Nov 2003
    Location
    Florida Panhandle
    Posts
    74

    Changing Linhof "Ground glass"

    Bob's answer startled me. Apparently the groundglass setup on my Tech V is incorrect. Here is what I have: A groundglass with grid, smooth side to the back of the camera, then beneath it (i.e., between the ground glass and the lens) a fresnel with its smooth side facing the lens. However, this fresnel is slightly smaller than the ground glass, so it fits inside the four shims that Bob mentioned. The groundglass itself rests upon the shims so I guess its 'ground' surface is in the correct position. I have the two fresnel clips but I think they are too far apart to hold the smaller fresnel that I have, if I were to move it from beneath the groundglass. Please comment.

    Thanks.
    Mike Lewis

  6. #6

    Changing Linhof "Ground glass"

    When your camera has the older style frsnel installed under the gg you will need to have the shims checked and positioned to re-set them for use with the fresnel on top. Yiu have the gg/fresnel set-up that was used on the III and IV models.

  7. #7

    Changing Linhof "Ground glass"

    Bob Salomon HP Marketing Corp and others,

    I'm using a Technika IV with fresnel/gg. The negatives are in poor focus. The fresnel/gg arrangement is as mentioned with (beginning at the lens) fresnel(smooth side), fresnel (patterned side), gg (etched side), gg (smooth side).

    Distance from the 147mm (I.D.) circular rim on the back's lens side to fresnel is 9.62mm, rim to cut film holder interior is 11.20mm, rim to Polaroid 545i interior is 11.64mm, rim to old-style Readyload holder interior is 11.11mm, rim to new style (black interior for single sheet Readyload) is 11.26mm. Fresnel thickness measures 1.91mm Processed ESTAR film base is 0.15mm Polaroid film thickness measures 0.05mm

    While the ~1.5mm to ~2mm offset between fresnel (lens side) and film plane places the gg at about the film surface distances I don't understand why the negatives aren't in focus. The negs are consistently off by about the same. All the glass is recent vintage multi-coated.

    Any ideas? I first thought the etched gg surface should be first with the fresnel last until I read your message. The 8.5mm x 99mm x 0.45mm gray paper shims I have are between the clips of about the same size and the threaded base. Am I missing some sizeable shims? Let me know what you think and thanks for your time.

  8. #8

    Changing Linhof "Ground glass"

    Steve Tharnstrom

    Linhof Service in the US is 973 808-9626. Ask them or the service center in your country. Be sure to let them know you have a IV.

  9. #9

    Changing Linhof "Ground glass"

    Steve, A camera can be designed to use almost any configuration of ground glass and fresnel, but the focus most be adjusted. Mis-installing a fresnel lens seems to be a common mistake. No definitive answer can be given to your problem without examining the camera in person: there are at least three possibilties. 1) The focus was originally adjusted for a plain ground glass, than someone installed the fresnel in front of the ground glass without changing the thickness of the shims and therefore switching the order of fresnel and ground glass should fix the problem. 2) The person who put the Fresnel lens in front of the ground glass adjusted the shims, but incorrectly. In this case switching the order of the fresnel and ground glass won't fix the problem. 3) You have some other difficulty in focusing.

    My opinion is that design choice of placing the ground glass first, with the ground side facing the lens, is by far the best -- this allows you to install or remove a fresnel lens (on the side of the ground glass away form the lens) as you wish without changing the focus.

    The image forms on the ground side of the ground glass. If you place any material in front of that surface, such as a Fresnel lens, you change the effective optical distance from the lens to the ground surface of the ground glass. The optical thickness of the Fresnel lens is different from its measured thickness because it has a higher index of refraction than light. So if you want to position the ground glass by measurement, and have a Fresnel lens in front, you have to include the difference between actual and optical thickness of the Fresnel in your calculations.

    If you want to set the focus by measurement, it would probably be more accurate to measure from a refererence surface on the back rather than from the lens. Probably few photographers have measuring equipment and skill accurate to set the focus this way. Plus, if you have the Fresnel in front of the ground glass you have to calculate the effective thickness based on its refractive index. You might do best having your camera adjusted by a professional camera repair person.

  10. #10

    Join Date
    Feb 2004
    Location
    Scottsdale, AZ
    Posts
    486

    Changing Linhof "Ground glass"

    Funny that this discussion happened today! I just got a Technika III (purchased from eBay) and I noticed that the Fresnel Lens sits towards the lens and NOT as with my Sinar behind the gg facing the viewer. I was just wondering why this would be the case. If I read Bob's posting correctly then the T IIIs and IVs had indeed such a strange setup!? I'll take the camera out tomorrow to see if the focusing is correct or not - the camera has definitely seen a lot of use, so I must assume that the person who had it before me was not having problems with the focus. Oh well - we'll see - thanks.

    Juergen
    Juergen

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