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Thread: A new line of Chinese pictorial lenses!

  1. #131

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    Re: A new line of Chinese pictorial lenses!

    Thank you,

    Now I have to investigate the problem of slight misfocus.

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    I focused on the eyes and I got the nose. It is a paper positive, not a contact.

    Quote Originally Posted by Mark Sawyer View Post
    Nearly all common round magnifying glasses are symmetrical convex lenses, so it doesn't matter which side faces the subject. Hope this helps!

  2. #132

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    Re: A new line of Chinese pictorial lenses!

    I've done more test and I definitively have a problem with the focus and I have no idea where it come from.

    So here is the scene (the ruler in in cm):

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    tiny airplanes from a kinder-egg.

    Here is the first picture with Nikkor-W 300mm at f:5.6 - 6 seconds
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    The focus is on the middle plane on the GG and on the paper.

    And here is the picture with the magnifying glass, wide open with the focus on the GG on the same middle plane. In the picture the plane in focus is in the front; 8 seconds exposure (a little bit to much)
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    I didn't change anything. I just focus on the GG, put the holder inside and took the picture.

    The camera is Agfa 8x10 but the paper is cut in 4 and kept with tape in the center of the holder, I don't want to waste good paper. This is direct positive (reversed). I tested this with two different holders and got the same result, the focus shift.

  3. #133
    Mark Sawyer's Avatar
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    Re: A new line of Chinese pictorial lenses!

    Off the top of my head, I'd say the magnifying glass is displaying chromatic aberration, where the blue light is focused closer than the rest of the visual spectrum. The paper you're using is blue-sensitive, and is capturing that blue light. The Nikkor-W is, of course, relatively apochromatic, so doesn't have that problem.
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  4. #134
    jp's Avatar
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    Re: A new line of Chinese pictorial lenses!

    Try putting the glass BEHIND the iris. Looks like it's at the front of your shutter/iris in the photo. Mark refers to the old problem documented of chemical/actinic focus. You could focus with a blue filter and/or get the iris working right so it can stop down and gain more DOF. Or just shoot some normal film to try it.

  5. #135

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    Re: A new line of Chinese pictorial lenses!

    I learned something new; chemical/actinic focus, thank you. Obviously this must be the problem.

    The shutter is a Compound 5, no iris but I can put the glass behind, the threads are identical.

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