# A ring of blades that never quite closes into a circle > A follow spot's iris is a ring of straight-edged blades, so it closes to a many-sided shape rather than a true circle, and only reads as round because its own edge is soft. August 19, 2026 · https://justog.club/stories/followspot-iris-circle Overlapping curved blades, closing down around a centre until the opening left is about a third open. Below the aperture, a cone widens softly toward the hem, brightest where it starts and fading out before it gets there. The opening isn't a circle. Nothing about it needs to be. ## What is an iris, and how does it actually close? An iris is a ring of thin curved blades set inside a lantern, overlapping like the plates of a fan, that slide together around a shared pivot to shrink or open the aperture the beam passes through. Moving the control shifts every blade the same amount at once, so the opening shrinks evenly from all sides rather than closing from one edge — the mechanism that lets an operator take a beam from a full body down to a tight head shot without the light appearing to slide off-centre. ## Why does a ring of straight-edged blades read as round? Because it doesn't have to be round. It only has to look round to an eye that isn't measuring it. A small number of overlapping curved blades produces a many-sided shape, not a true circle, and a perfectly sharp-edged version of that shape would show its corners. What hides them is the blur at the aperture's own edge, which every real beam has, since the blades aren't optically flat against the light source. Softness is doing the rounding that geometry doesn't quite manage. ## Why does a follow spot keep a soft edge rather than a hard one? Because a hard-edged circle tracking a moving person reads as being caught in something, not lit by something. A little softness at the perimeter turns a spot of light into an implied space around the performer rather than a ring drawn on top of them — the beam stops looking like it's isolating a target and starts looking like it's simply where the attention is. The blade geometry and the way it reads to an audience happen to want exactly the same thing. ## What makes a good version of this design? Letting the aperture stay visibly imperfect — a few blades slightly uneven, the shape just short of true, edges soft rather than crisp — rather than drawing the tidy perfect circle a first attempt usually reaches for. A too-regular iris looks like a camera lens, which is a different object doing a different job. The slight irregularity, plus a cone that fades rather than stops, is what reads as a beam of stage light rather than a generic aperture graphic. ## Who owns the shape of an iris, or a beam of light? Nobody. A ring of overlapping blades and a cone of light describe how the equipment and the physics behave, not a design anyone holds. A specific lantern model, its casing and its badge belong to the manufacturer that made it, licensable the ordinary way if a real make is the point. An unbranded iris, drawn from how the mechanism actually works, needs nobody's permission. ## Does this design only make sense for stage lighting? The mechanism turns up anywhere a variable circular opening is needed — a camera lens aperture is built the same way, as is a telescope's field stop. What's specific to a follow spot is the cone beneath it, doing real work in haze or dust, [the medium that turns a beam into an object you can watch cross a room](/stories/haze-beam-in-air). Without that cone, an iris on its own reads as a mechanism; with it, it reads unmistakably as theatre lighting. In the same lantern, closer to the lamp, sits [a steel disc doing the opposite job — cutting a pattern rather than closing to an aperture](/stories/gobo-pattern-disc). ## Does it print well? Yes, provided the soft edges stay soft — one of the few designs here where a hint of gradient earns its place, right at the aperture's rim and down the length of the cone. Keep the blade lines themselves crisp and few in number; it's the light, not the mechanism, that should look soft. Near-black ground, cream for the blades, warm white for the brightest part of the beam — two tones of pale against dark carries both the hard mechanism and the soft light it shapes. ## How do I get one made? Describe your beam at [JustOG](/) — how far closed the iris should read, and how far the cone should travel down the shirt. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped. Designs other people have published are in the [shop](/shop). A ring of blades closed to a third, and a cone of light with nothing solid in its way.