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an_iris_by_any_other_name.jpg

Right, so, here’s a question for the nomenclaturally aware mechanical engineers in the audience. Last weekend, I was exposed to two equally awesome objects that include radially-opening apertures that I call “irises.” The first, to left, is Alan Rorie’s Aperture Lamp, which includes an adjustable opening to control the amount of light it emits. The second, to right, is Christopher Schaie’s brass peephole cover. Note the significant difference between these two mechanisms: Alan’s has thin leaves that overlap, Christopher’s has thicker leaves that do not overlap. Now here’s my question: Are there distinct names for these two mechanisms? And if so, what are they?

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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Comments

  1. ZNahum says:

    You could call it a shutter, because it is the same style of how a shutter works in a camera.

  2. migpics says:

    According to Wikipedia under shutter you have two different types. A leaf shutter and a diaphragm shutter.
    The first one is a diaphragm shutter which “… is a type of leaf shutter consisting of a number of thin blades which briefly uncover the camera aperture to make the exposure.”

    The leaf shutter is the one on the right or the second one which “is a type of camera shutter consisting of a mechanism with one or more pivoting metal leaves which normally does not allow light through the lens onto the film, but which when triggered opens the shutter by moving the leaves to uncover the lens for the required time to make an exposure, then shuts.”

    I don’t know if there is a distinction between overlapping or not.

  3. theophrastus says:

    Excellent question! and there’s very little, on the intertubes at least, about engineering for optimum iris blade/leaf/vane (which is it?) shape and number. There are probably wonderful unscanned texts (19th century?) which discourse endlessly about the curve of the track that actuates the blade; perhaps optimizing it for speed (some sort of brachistochrone??).

  4. Colecoman1982 says:

    “Are there distinct names for these two mechanisms?”

    Yes. According to the summary, they are referred to as “Aperture Lamp” and “brass peephole cover” respectively.

    (Sorry, I couldn’t resist.)

  5. Scott says:

    The mechanism on the left is called an ‘iris’ or ‘iris mechanism’.

    It’s been a few years, but at the end of “Empire Strikes Back”, the “door” on the Millennium Falcon through which Luke Skywalker is rescued from Cloud City features the mechanism on the right.

  6. Sam Ley says:

    The one with the overlapping leaves fits the most common description of “iris”, as it is used in modern cameras. Modern SLR lenses have somewhere between 5 and 9 blades in their irises (with some exceptions). The number of blades can change the shape and “quality” of the bokeh – the out-of-focus portion of an image – which has a dramatic, but hard to put your finger on, affect on the quality of a photograph.

    Because the exact shape of the iris has a big affect on the appearance of the out of focus area, the second “iris” shown, the brass one, would probably never be used in a real camera, because when it is partially closed, it would have a crazy shape that would cause a lot of diffraction.

    I don’t think either resembles a camera shutter either – shutters are supposed to ensure that each part of the sensor plane (or film) is exposed for the same amount of time – modern SLRs do this by having a “curtain” open from the bottom up, then close from the bottom up so that each part of the sensor is exposed for the same amount of time (even though it isn’t all exposed at the same time). A circular or iris shutter would always expose the center a lot more than the edges.

  7. Iceman086 says:

    The Iris Mechanism on the left was probably made in the same manor that iris’ in lighting instruments for the stage (fresnel’s) are made. Below is a quick video that I shot of one that I pulled from a light.

    When I took this Iris Mechanism apart I found that it had several parts to it that were all slightly different.

    The blades were a C shape with a peg at both ends. If the blade was standing on end liked a C, then the peg on the top was on the front of the blade and the peg on the bottom was on the back side.

    There were also 2 rings called that the pegs on the blades slotted into it. The first ring had a set of holes that were centered and placed evenly throughout the first ring.

    The second ring had oval shaped holes that were also spread out evenly.

    The leaves are placed into the holes in the first ring and then as they are placed into the ring begin to overlap one another. The cool thing here is that when the second ring is placed on onto the pegs that are on the back side of the blades it allows for the opening and closing of the Iris. So when the rings are twisted opposite of one another the Iris closes.

    The reason for the oval shape in the second ring is to allow the pegs in the blades to move forward and backward as well as to allow them to spin as the mechanism is used.

    I recently made a blanking die and created my own version of this on a smaller scale that is to be used in a set of steam punk goggles. I should have it done very soon.

    Hope this helps!

    1. Almost Scientific says:

      Hey Iceman086 –

      I’m Almost Scientific the designer and fabricator of the Aperture Lamp.

      The aperture in the lamp is very similar in design and was made from scratch.

      The hardest part of making it was fastening the two pins. They need to be flush on both sides so they can slide past each other. I could not use any methods involving heat as it would warp the 0.026″ brass that I cut the blades out of.

      In the end I used a rivet style attachment that I then brought back int plane.

      The other small snag is that the pin that rides in the cam (the slotted ring) is not in the middle of the blade, but slightly offset.

      Good luck with you goggles!

      Send me some photos or video when you’ve got the done!

      Ya’all can find out more about me and my work here:

      http://www.AlmostScientific.com

      and if you use Facebook you can find me here:

      http://www.facebook.com/home.php?#!/pages/Almost-Scientific/282522968385?ref=ts

  8. Jake Bailey says:

    I would call the one on the left an iris. It’s much more like the human iris, and it’s the same as the Stargate Iris.

    I have no idea what to call the one on the right though.

  9. pete says:

    Well, to be fair each one emits light when they are open. One is manufactured light and the other reflected light. Although the latter assumes a light source to produce light to reflect. A peephole would be fairly useless if you couldn’t see what was on the other side.

  10. oskay says:

    The distinction between a diaphragm and a shutter is that a shutter closes all the way– to block light –while a diaphragm does not. The mechanism on the left is common in optics, and has the well-established name “iris diaphragm.” The version on the right is less common, but is generally considered to be another type of iris diaphragm.

    http://commons.wikimedia.org/wiki/File:Diaphragm_iris_types.svg

    From the pictures alone, I’d guess that the one on the left closes partially, while the one on the right closes almost fully– so it could be considered a “window shutter,” but probably not a shutter in the optics sense.

  11. Simon says:

    For years I had what I called an Iris aperture on my key ring. It was brass and had black vanes on it and by I was always fascinated by the mechanism and how the little pins ran in the grooves to make the thing open and close. I remember taking ti apart and reassembling ti many time. Alas it fell off the keyring somewhere one day (at the metal dealers I think) and so it is no more. I’ve always thought about pulling apart an old camera lens to get a new one. I originally got it from some surplus lens assembly I think. And as other have mentioned they won’t close completely so they will never totally block all the light.

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