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Thread: Imagon again

  1. #1

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    Imagon again

    Hi to all,


    I have a 360mm Imagon in a Compound 5 shutter lying around for quite some time and now want to start using it.

    I guess I have read every possible thread concerning the use of Imagon lenses, but I must have missed something essential, or I am completely lost in outer space.

    The lens has the 3 original disks :

    H 5,8 – H 7,7
    H 7,7 – H 9.5
    H 9,5 – H 11.5

    I am aware that we are talking here about H-stops, not F-stops. (whatever the H stands for)

    1) My question, in terms of light measurement, what F-stops do the H-stops correspond to ?


    2) In order to use the Imagon lens without any of the three disks, but using the diaphragm of the Compound shutter, it would be useful to calibrate the F-stops settings.

    The maximum opening of the shutter being 64mm, according to the F/D rule, this would give us a maximum aperture of 5,6.

    Am I right in applying the same rule to determine the respective F-stop ?


    3) Let’s now come back to the 3 original disks :

    H 5,8 (center disk and small disks open) – H 7,7 (only center disk open, opening 38 mm)
    H 7,7 (center disk and small disks open) – H 9,5 (only center disk open, opening 31,5 mm)
    H 9,5 (center disk and small disks open) – H 11.5 (only center disk open, opening 26 mm)

    If I apply the same F/D rule to the 3 disks with only the center disk open, I would obtain the following F-stops :

    360mm / 38mm = F-stop 9,47
    360mm / 31.5mm = F-stop 11,43
    360mm / 36mm = F-stop 13.85

    The F-stop numbers have strange similarities again with the H-numbers.

    Is this reasoning correct, or am I wrong ?

    4) Does someone out there have for sale the book from Alfons Scholz on the Imagon lens ?


    That’s it. Hope you could follow my reasoning.

    Thank’s in advance for your help.


    Thierry

  2. #2

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    Re: Imagon again

    Hi Thierry

    The H stands for the german word "Helligkeit" wich means brightness!
    ANd it further explains: "Thus as a setting of H 5.8 the picture should be exposed as with a lens stopped down to f 5.8 Don't worry about this description; in exposure therms, H- values operate exactly like traditional f stops."
    And you always should fokus with the aperture diapragms wich you are use for the shoot, but for fokusing you should always close the smaller holes!
    And after fokusing you can open it again if you like it!
    Thads all to it!
    Hope it helps, Armin Seeholzer

  3. #3

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    Re: Imagon again

    Armin, I have always focused using the actual disk I intended on shooting with, but I focused at whatever setting of the small holes that I was going to use for the image. Was that wrong? It is easier to focus with the smaller holes closed, but it also increases the apparent DOF and I assumed that was similar to focusing a lens at f16 then shooting at F8 which obviously is incorrect.

  4. #4
    Ted Harris's Avatar
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    Re: Imagon again

    According to Bob Salomon, and my experience, focusing at the taking aperture works best.

  5. #5

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    Re: Imagon again

    The maximum opening of the shutter being 64mm, according to the F/D rule, this would give us a maximum aperture of 5,6.

    Am I right in applying the same rule to determine the respective F-stop ?


    Yes, but the slight discrepancy your are observing between your calculation and what is engraved for the minimum H-stop with peripheral apertures closed might be explained by
    - the fact that the actual focal lenght could differ from 360mm by a few percent,
    - the fact that the Compound iris is probably not located where the special Imagon variable iris is located.

    I have a shutterless Imagon, and one can say that this is a rare example where the iris diameter that you can measure on the iris is exactly the same to be used for the F/D computation.
    The technical reason is that the F/D number has to be computed with the diameter of the entrance pupil i.e. the image of the iris as viewed from the entrance side. In the shutterless Imagon, the entrance pupil is the iris itself...
    My understanding for the shutterred Imagon is that the special iris is still in frornt, but that the shutter iris is behind the lesn elements. Am-I right ?

    But as mentioned, simply use the H-stop values as engraved, this should work.
    The fact that Rodenstock mentions something different than F-stops is probably explained by the fact that the H-numbers cannot be used to compute regular Depth If Field values.

  6. #6

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    Re: Imagon again

    Quote Originally Posted by Emmanuel BIGLER View Post
    .....My understanding for the shutterred Imagon is that the special iris is still in frornt, but that the shutter iris is behind the lesn elements. Am-I right ?.......
    From the back to the front in my shuttered Imagon 300 is the Lens, the shutter iris, and finally the special iris. So both shutter iris and special iris are in front of the lens, but separated by several mm.

  7. #7

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    Re: Imagon again

    Hi
    I just stated what Rodenstock has written in there explanation how to use the Imagon!

    No rumors just what they stated and also worked fine for me!
    You can focus with the small holes open but it is much more difficult, Rodenstock even stated thad it will give a tiny bit of focus shift but they say also the Imagon has enough DOF for compensating it!
    Hope it helps, Armin Seeholzer

  8. #8

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    Re: Imagon again

    Hi to all,

    Thank's a lot for your input and help.

    It's good to know you're out there when advice is needed.

    Thank's again and best regards.

    Thierry

  9. #9

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    Re: Imagon again

    /Users/leenadel/Desktop/lee024.jpg

  10. #10
    loujon
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    Re: Imagon again

    Quote Originally Posted by lee nadel View Post
    /Users/leenadel/Desktop/lee024.jpg
    Huh?

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