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  1. #1
    Terrance Hounsell's Avatar
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    110mm Super Symmar XL VERSUS 0.450mm Pinhole

    I started working on a somewhat interesting project that involves taking duplicate images with both the 110mm Super Symmar XL (super sharp) and a 0.450mm pinhole and comparing them from an aesthetic point of view. For the most part I will be shooting the 110mm @ f/5.6 (wide open) as compared to the 0.450mm pinhole @ f/245. According to most pinhole calculators this pinhole should be optimum for the 110mm focal length.

    To accomplish this project I have a Copal #1 shutter with a screw in adapter that holds the pinhole close to the shutter blades so as to be close to the nodal point of most lenses. The shutter is mounted on a lens board so that I can take the odd numbered sides of my 4x5 film holders with the 110 and then without moving or changing anything on the camera (a 4x5 Wisner Expedition) I can swap lens boards and duplicate the image on the even numbered sides of the film holders using the pinhole.

    This past weekend I tried my first set of exposures. The subject was architectural (an old stone Masonic Temple). I processed the film last night and made an interesting discovery; aside from the expected differences in sharpness and depth of field there was a substantial difference in magification. I wasn't expecting this because the focal length didn't change and the pinhole was near the nodal point of the lens. The difference in magnification is roughly 20-25%. Can someone explain to me what is happening?

    For what it is worth I will also mention that I was using extreme front rise to correct parallax in the building. The pinhole actually vignetted about 3/4" into the frame perhaps the image was being cut off by the rear of the shutter. This probably has nothing to do with the magnification issue but I am throwing it in anyway.
    Experience is a wonderful thing. It enables you to recognize a mistake when you make it again.

  2. #2

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    Can you scan and post some images? Not claiming to have any ideas, but it would be interesting to see the differences.

    Have you checked the viewing angles for your pinhole? There is an online calculator at www.mrpinhole.com or one built into Pinhole Designer that you might want to try. I think Pinhole Designer may have a magnification calculator too.

  3. #3

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    the schneider projects a larger image circle (288 @ f22) than the pinhole (211) the angle of coverage for the lens is 105 and with the pinhole is 73 this should account for the differences your seeing.

    the lens chart can be found here:
    http://www.largeformatphotography.in...es/LF4x5in.xls

    and i used the mrpinhole.com calculator for the pinhole information.

    hope this helps.

    tom
    www.f295.org

  4. #4
    Helen B's Avatar
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    The flange focal distance of the 110 SSXL is 117.2 mm at infinity, so you should move the front panel backwards to compensate when using the pinhole. The rear nodal point of the lens is about 7 mm behind the flange - and that is where the pinhole should be. Strictly speaking, you should move the back forwards rather than the front backwards to keep the same perspective.

    The pinhole should be where the entrance pupil of the SSXL was (ie where the aperture appears to be, not where it is), and the distance from the pinhole to the film plane should be 7 mm less than the distance from the SSXL flange to the film.

    Best,
    Helen
    Last edited by Helen B; 09-27-2006 at 09:47 AM. Click to view previous post history.

  5. #5

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    Helen You are so very knowledgeable. You technical knowledge is only exceeded by the acuity of your vision and the beauty of your person.
    Claire (Ms Anne Thrope is in the darkroom)

  6. #6
    Jim Jones's Avatar
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    Before embarking on a serious pinhole project, I suggest doing some homework in optimum pinhole diameters. Calculating pinhole diameters is as much an art as science. The application of the pinhole should be considered, not merely the theoretical calculations. Many pinhole calculators give diameters that sacrifice central resolution in favor of off-axis sharpness. Using PinholeDesigner with a user constant of 1.5 (verified through testing) gives near optimum on-axis sharpness with a pinhole diameter of about .37mm in your camera. The on-axis resolution will be perhaps three line pairs per mm, or slightly better. Remember, resolution measurements of diffraction limited optics with a standard resolution target is somewhat unreliable. The resolution will fall off significantly towards the edge of the image. When using extreme front rise with a pinhole, the axis of the pinhole should be pointed somewhat towards the bottom of the film for optimum sharpness and illumination. Angular coverage of pinholes is a hotly debated subject. Some claim a 110mm pinhole has a usable image circle as large as 380mm. Corner sharpness and illumination suffer greatly with that coverage, although it works fairly well on curved film.

  7. #7
    Terrance Hounsell's Avatar
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    Thanks for all of your answers. I was aware of the position of the nodal point of the 110mm SSXL and had previously considered this to be relatively minor in the scheme of things. I can't see how it accounts for an approximately 25% change in image size on the film. At this point I am leaning towards operator error (me) and the possibility that the camera may somehow have changed focus when I was changing from lens to pinhole. The camera was in an extremely awkward position at the time and keeking my balance was difficult.

    I don't have time to contact print these negatives and scan them for you but to eliminate operator error I will process another pair of lens/pinhole negatives with a batch I am doing tonight. The subject is a receeding series of waterfalls and the movement is limited to a tiny amount of front tilt. I will check to see if there is any difference in image size when they are dry in the morning and report back.

    Thanks again
    Experience is a wonderful thing. It enables you to recognize a mistake when you make it again.

  8. #8
    Helen B's Avatar
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    Well, if you are referring to area, then having the pinhole 12 mm in front of the rear nodal point of the 110 SSXL (ie from ~7 mm behind the flange to ~5 mm in front) would give a 25% increase in image size.

    Best,
    Helen

  9. #9
    Terrance Hounsell's Avatar
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    Measured negatives/ moving pinhole

    I measured a fixed horizontal dimension (building lintel) in both architectural negatives: 29.5mm for 110mm SSXL as compared to 36mm for 0.450mm pinhole. This is a linear increase of 22% for the pinhole.

    I developed a second pair of negatives last night and measured a fixed vertical dimension (a rock face) in both landscape negatives: 40mm for 110mm SSXL as compared to 44mm for 0.450mm pinhole. This is a linear increase of 10% for the pinhole.

    The difference may be due to the fact that I was approx 100 feet from the building but only 10 feet from the rock in the water falls.

    In any event I am going to look at my Copal #1 shutter to see if I can screw the adapter into the rear threads (the diameter may not be the same). I haven't checked the dimensions yet but if this works it should get the pinhole nearer to the nodal point of the lens.

    As I would like to display the final images in pairs (lens vs pinhole) it would be nice if they were near enough exactly the same size so that the viewer could concentrate on the difference in other characteristics.
    Experience is a wonderful thing. It enables you to recognize a mistake when you make it again.

  10. #10
    Helen B's Avatar
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    Couldn't you mark a piece of paper or something with the required displacement, then hold or clip it to the bed as you moved the standard?

    Best,
    Helen

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