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  1. #11

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    f/stop = lens-focal-length/aperture-hole-diameter.
    So with the 80 mm Planar at f/8, the aperture hole diameter is 10 mm.
    Because of the teleconverter, the effective focal length will increase with the factor of the teleconverter; 1.4 x 80 mm = 112 mm

  2. #12

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    Thank you spijker, but I still have some questions: does the location of the hole in relationship to the lens (in this case in front) affect the diameter? should I consider drilling the holes for my lens without the 2x teleconverter and then apply the factor? does the 34mm extension ring affect this values whatsoever?

  3. #13

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    Extension tube do not affect your aperture calculations. They simply affect magnification, length of tube/focal length of lens = magnification. 50 mm tube/50 mm lens = 1.0 magnification. Even with shooting through a hole in your lens cap, you're only going to get a small circle in a field of black. If the aperture diaphragm isn't in the optical center of the lens you're always going to get vignetting.


    -Xander

  4. #14

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    Quote Originally Posted by Fast14riot View Post
    Extension tube do not affect your aperture calculations.
    But extension tubes may affect your exposure calculations.

    With LF cameras, as you move the lens farther and farther from the film plane, there's a point at which a "bellows factor" must be applied to your exposure calculations. This is to compensate for the loss of light intensity due to the increased distance the light must travel to reach the film.

    The same principle holds with extension tubes on a 35mm camera.

  5. #15

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    aca91, do yourself a favor and make a hole in a piece of paper or thin cardboard before you waste lens cap. My regular 3-hole puncher for paper binders does a 7 mm hole, so that would be f/11 for a 80 mm lens. With the 2x teleconverter it would be f/22 since now you have a 160 mm lens. Hold the paper with the hold in front of your lens where the lens cap would be. Through the viewfinder of the Nikon you'll see that the "picture" is heavily vignetted. If you like that, then go for it and modify a lens cap.

  6. #16

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    SKEPTICAL!! Luckily, I did myself "the favor" and I'm now sharing the result. The first picture was taken with the lens wide open, while the second one had a cheap piece of cardboard with a hole of approximately 4.5mm diameter. The third picture is just the setup taken with an ipad. I think this fast experiment delivers very good results, any suggestions? Imagine that if this works with lens caps, they could be painted white and avoid almost any reflections, even the ones from the lens, in jewellery photography or other kinds of products.
    Attached Thumbnails Attached Thumbnails Macro (1 of 3).jpg   Macro (2 of 3).jpg   Macro (3 of 3).jpg  

  7. #17

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    Well, I'll have to say that I'm quite surprised by the results. As your pictures show, the vignetting seems to be non-existent despite the fact that the "aperture" is not in the optical center of the lens. Unless you removed the vignetting in Lightroom. Good for you! But a D800 .. on APUG .. naughty boy! (I don't care)

  8. #18

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    You have my word that I didn't touch them on lightroom, as for the D800 I agree it's out of place, but this is about optics that could be used with any Nikon body . Now, back to the topic, with this kind of magnification, what would you do? Maybe drill an equivalent to an f/32 to get an f/64 with the teleconverter, or an f/45 to get an f/90?

  9. #19

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    The aperture doesn't have to be Centered optically.
    Perar currently has at least one lens with the apertures in front of the optics. If you use a convertible lens on a view camera the aperture can be either in front of or behind the optics.
    The results may not be optimum but still it does work.
    Heavily sedated for your protection.

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