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  1. #1
    Willie Jan's Avatar
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    3:1 and beyond macro photography with 4x5

    In a previous post I had some problems with focusing my 4x5 cambo when using 2:1 and beyound. The image was not sharp (wrong focus).

    I now have a solution for this.

    I made a piece of glass which fits in my 4x5 when the back is removed.

    The thickness of the glass is made at 4.8mm (2 pieces of glass filled up at the sides until 4.8).
    I measured the distance from a 4x5 fidelity cassette with a micrometer to film of 5mm, With film it is around 4.8mm. So my glass is now at the position where the film is located.

    I now put on the normal back and focused the image (3:1).
    I removed the back, added the plain glass and refocused with a 10x peak loupe at the air image which is very bright {I do not know the right english name} (NL: luchtbeeld). WOOOOOW! The distance between the focus back and this is 8mm more to the front.

    I do have to print the neg, but it looks sharp to me.

    Is there anyone who did notice the same?
    I never had this problem when using 1:1.
    Looks like focusing is becoming very specific beyond the 1:1 and that there is some mathematical error that is getting quadratic larger beyond this 1:1.

    I do use a normal cambo back where the ground glass is a original cambo and it is positioned in the right way. Only at these micro enlargements I get these problems.

  2. #2
    Bosaiya's Avatar
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    The film plane should be at the same distance as the ground glass, shouldn't it? I don't have these problems you describe when going to 12:1 and beyond on 4x5".

    I have found that loading the film holder into the back while it is still attached to the camera can cause a shift in focus because of the bump. As a solution I simply remove the entire back, load the holder, and gently return the back.

  3. #3

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    It would suggest that the focussing screen is way off in the Cambo.
    Are you sure that it is not backwards?

    It isn't something caused by magnification, of course, but that will make it more obvious perhaps.

  4. #4
    Willie Jan's Avatar
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    until now i did not have any problems with focusing.
    The only thing that changed is the amount of magnification and the time.

    I did a test yesterday with ortho film so that i could develop it fast and saw indeed that it was sharper(better focused?) when looking at the airimage in stead of the groundglass. I am now wondering it the time (2-3 minutes) also could have an impact since the whole image is not sharp. When different focused, there should be somewhere a sharp point. But in stead the whole image looks unsharp. I always close the windows and stand still during exposure.

  5. #5
    Bosaiya's Avatar
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    There are only so many possibilities. You're going to have to eliminate variables until you find the right one(s). Time won't change anything unless something changes during that time. I have seen a lot of strange things happen while waiting for long exposures, but so far none of them have been supernatural.

    I'd start by testing with a different camera.

  6. #6
    Willie Jan's Avatar
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    Did some extra tests and it looks like there is something wrong with the lens.

    My 150 5.6 rodenstock sironar-n looks better (crispier/sharper/more detailed) at the ground glass than this 120 apo macro.

    I am sending it to rodenstock.
    They replied very quick on my mail.



 

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