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Ballpoint pen tip seen through my bellows

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  • #16
    Re: Ballpoint pen tip seen through my bellows

    Originally posted by PeterD View Post
    Thanks for your post John and also for pointing me back to the olympus site. Looking at the origin of this post (From OlyFlyer), It still leaves me the question how efficient is the SSWF. I am assuming that that the balloint images were made using a SSWF fitted camera.

    Best regards

    PeterD
    I can only relate my own experience. Prior to getting an E-1 I used a Nikon D70, dust spots were visible in images even when displayed at 800x600 uncropped when the camera was less than 6 months old. I have yet to see dust spots on a shot taken using the E-1.

    The actual vibration of SSWF is only one part of the Olympus anti dust system, the distance that the membrane sits from the sensor also plays a part.

    Richard
    In theory there's no difference between theory and practice but in practice there is.

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    • #17
      Re: Ballpoint pen tip seen through my bellows

      Originally posted by theMusicMan View Post
      Please excuse my ignorance here, but wouldn't these alleges dust specs turn up on any and every image if the images are 100% framed...? If you use a bellows, isn't all that happens is that one gets to see a close-up highly magnified image of the subject matter - that then fits on the same sized sensor as if one had taken an image of a landscape view at 3 miles away?

      There are the same number of pixels on the image i.e. approx 3.5k x 2.5k, and as such wouldn't the alleged dirt/pollen specs still show up. The fact that a bellows is used shouldn't make a bit of difference as far as I can tell.

      I will of course bow to the better knowledge of experienced photographers, but please do convince me because as of now, I can't see a bellows making any difference. If there's dirt on the sensor, it would show on any image.
      You are absolutely right that using bellows to get a super macro image, or using a wide angle to get a super wide angle landscape image uses the same number of pixels. The problem is the aperture. You can never set the same aperture with any lens as the effective aperure using the bellows. When using bellows or any other extension, like tele converters or macro converters or simple extension tubes the actual effective aperture is increased, that is one reason why converters cause light loss and demand increase of shutter speed. Using the bellows in my case, the extension was 245mm to get the 16:1 magnification. I had the lens set to f/22 and used a 35 mm lens at infinity. Now, the effective aperture can quite easily be calculated using the formula below.

      Ef = Effective f-value (that is what you get after adding extension tubes or bellows)
      If = Indicated f-value (that is shown on your lens or display, the one that is set on the lens)
      F = Focal length of the lens
      Ex = Extension (total length of the extension tube or bellows)


      The formula is: Ef = If x (F + Ex)/F

      In my example, with a 35 mm lens and a 245mm extension tube you get ~16:1 magnification and if the lens is set to f/22.0 than:

      Ef = 22 x (35 + 245) / 35
      The result of the above is 176 (!)

      As the aperture opening becomes smaller and smaller, more and more details can be seen nearer and nearer the CCD. Using any lens normally, the effective aperture is the same as the selected aprture. I assume if you would be able to select f/176 on any other lens, that you'd see the problem with that lens as well, but as it is, f/22 being the minimum, we can not see it as clearly as with bellows. Also, as the magnification and the extension is more and more reduced, less and less can be seen. The dirt is there on the same CCD, but can not bee seen as clearly, since it is too much out of focus, as you can see in my sky image example, taken just one day apart.

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      • #18
        Re: Ballpoint pen tip seen through my bellows

        Woah OlyFlyer - that's some superb explanation, thanks for this. I can say with 100% certainty, that I have absolutely learned something new today - thanks...
        John

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        • #19
          Re: Ballpoint pen tip seen through my bellows

          Originally posted by R MacE View Post
          The actual vibration of SSWF is only one part of the Olympus anti dust system, the distance that the membrane sits from the sensor also plays a part.

          Richard
          Hi Richard,

          I was going to say that. That is exactly what the second reason why it is not clearly visible in normal images. The E-system has a very thin transparant membrane in front of the sensor. It is that membrane which gets shake, not the CCD. As there is room between the membrane and the CCD, if the specs get stuck on the membrane, those are a bit out from the CCD creating an OOF effect, which is very good for normal photography. Without the membrane, we'd probably had to clean our CCD much more often.

          Now, it can be the case that my SSWF just stopped functioning, I don't know it yet. But, it definitely is a good and efficient thing in my opinion.

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          • #20
            Re: Ballpoint pen tip seen through my bellows

            Originally posted by theMusicMan View Post
            Woah OlyFlyer - that's some superb explanation, thanks for this. I can say with 100% certainty, that I have absolutely learned something new today - thanks...
            I appreciate you saying that. It really warms my heart. Thanks.

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            • #21
              Re: Ballpoint pen tip seen through my bellows

              Hi Olyflyer, like Musicman I'd also like to say thanks for your explanation of the effect using bellows has on effective aperture.
              In theory there's no difference between theory and practice but in practice there is.

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              • #22
                Re: Ballpoint pen tip seen through my bellows

                Originally posted by R MacE View Post
                Hi Olyflyer, like Musicman I'd also like to say thanks for your explanation of the effect using bellows has on effective aperture.
                Of course, I appreciate you saying that as well, but actually I stole the text. The original source is this one:

                http://olyflyer.blogspot.com/2007/06...erture-in.html

                Anyway, I hope if I am wrong, somebody will correct me.

                Comment


                • #23
                  Re: Ballpoint pen tip seen through my bellows

                  How about this for an explanation of the visible dust spots?

                  I've spent an hour with 'Inkscape' to produce what I think may produce the obvious dust spots. I'm not really up to speed with Inkscape, so forgive the rough diagrams.

                  The top diagram shows the light path through a large aperture, producing a large but diffuse and faint image on the sensor. In most cases I guess the image it produces is too faint to notice, but perhaps if the region is located, the dropper tool in PS may show a slight difference from the surrounding region.

                  The bottom diagram shows the light path through a small aperture. As can be seen the rays are getting near parallel, such as to produce a smaller but darker and sharper image than above.



                  Shoot me down if you think different!
                  ;^)

                  Jim Ford

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                  • #24
                    Re: Ballpoint pen tip seen through my bellows

                    I won't shoot you because what you say is true. This is what is happening, and at that effective aperture of 176, it is not strange at all that it is more disturbing than in normal images. Now that I know where the spots are, I can locate them also in my sky images, but without the super macro, I would not even see them.

                    Thank you for the drawing.

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