diff --git a/crates/engine/src/commands/focus.rs b/crates/engine/src/commands/focus.rs
index 013672a38..356ce1a07 100644
--- a/crates/engine/src/commands/focus.rs
+++ b/crates/engine/src/commands/focus.rs
@@ -78,6 +78,12 @@ fn set_to_layer(s: &mut Session, p: &Value) -> Result<Value> {
     let c = "camera.setFocusToLayer";
     let (cid, cam, target) = refs(s, p, c, true)?;
     let d = focus_depth(s, cid, cam, target.ok_or_else(|| bad(c, "no layer"))?).ok_or_else(|| bad(c, "can't evaluate the layers"))?;
+    // Only a finite depth can be stored: JSON has no infinity or NaN, so the project could no
+    // longer be saved. Extreme but finite positions can still produce one, and `d <= 0.0` is
+    // false for NaN.
+    if !d.is_finite() {
+        return Err(bad(c, "can't measure the distance to the layer (the camera or layer position is out of range)"));
+    }
     if d <= 0.0 {
         return Err(bad(c, "the layer is behind the camera"));
     }
diff --git a/crates/engine/src/tests_tail.rs b/crates/engine/src/tests_tail.rs
index 2710365eb..90cfd1bfc 100644
--- a/crates/engine/src/tests_tail.rs
+++ b/crates/engine/src/tests_tail.rs
@@ -421,6 +421,70 @@ fn camera_focus_commands_undo_and_serde() {
     assert!(s.execute("camera.linkFocusToPoi", json!({})).is_ok());
 }
 
+/// Set Focus Distance to Layer: degenerate targets (behind the camera, exactly at it) are clean
+/// errors, and a depth-of-field frame renders right after the command.
+#[test]
+fn camera_set_focus_to_layer_degenerate_targets_and_dof_frame() {
+    let mut s = comp(400, 300);
+    let t = s.execute("layer.newSolid", json!({"color": "#ffffff", "width": 50, "height": 50})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.setSwitch", json!({"layers": [t], "switch": "threeD", "value": true})).unwrap();
+    let cam = s.execute("layer.newCamera", json!({})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": cam, "path": "transform/position", "value": [200, 150, -500]})).unwrap();
+    s.execute("prop.set", json!({"layer": cam, "path": "cameraOptions/dof", "value": true})).unwrap();
+    s.execute("layer.select", json!({"layers": [cam, t]})).unwrap();
+    // Behind the camera (which now sits at z = −500 looking towards +z).
+    s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [200, 150, -1000]})).unwrap();
+    let e = s.execute("camera.setFocusToLayer", json!({})).unwrap_err().to_string();
+    assert!(e.contains("behind the camera"), "{e}");
+    // Exactly at the camera: depth 0, still a clean error.
+    s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [200, 150, -500]})).unwrap();
+    assert!(s.execute("camera.setFocusToLayer", json!({})).is_err());
+    // In front: the command works, and the depth-of-field frame renders with finite pixels.
+    s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [200, 150, 400]})).unwrap();
+    let d = s.execute("camera.setFocusToLayer", json!({})).unwrap()["focusDistance"].as_f64().unwrap();
+    assert!((d - 900.0).abs() < 1e-6, "{d}");
+    // An out-of-focus 3D layer, which must visibly blur, and a 0%-scaled one, whose pixels cover
+    // ~0 screen pixels and so turn an ordinary defocus into a radius of ~1e9 buffer pixels.
+    s.execute("prop.set", json!({"layer": cam, "path": "cameraOptions/aperture", "value": 120})).unwrap();
+    let blur = s.execute("layer.newSolid", json!({"color": "#00ff00", "width": 60, "height": 60})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.setSwitch", json!({"layers": [blur], "switch": "threeD", "value": true})).unwrap();
+    s.execute("layer.setTransform", json!({"layer": blur, "prop": "position", "value": [200, 150, 1200]})).unwrap();
+    let invis = s.execute("layer.newSolid", json!({"color": "#ff0000", "width": 40, "height": 40})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.setSwitch", json!({"layers": [invis], "switch": "threeD", "value": true})).unwrap();
+    s.execute("layer.setTransform", json!({"layer": invis, "prop": "position", "value": [200, 150, 1600]})).unwrap();
+    s.execute("layer.setTransform", json!({"layer": invis, "prop": "scale", "value": [0.0, 0.0, 0.0]})).unwrap();
+    let cid = s.active_comp_id().unwrap();
+    let img = s.render(cid, effectcraft_time::Tick::ZERO, Default::default());
+    assert!(img.data.iter().all(|p| p.iter().all(|c| c.is_finite())), "non-finite pixels after setFocusToLayer");
+    // The DoF frame actually blurred (not a no-op blur): the same frame with DoF off differs.
+    s.execute("prop.set", json!({"layer": cam, "path": "cameraOptions/dof", "value": false})).unwrap();
+    let plain = s.render(cid, effectcraft_time::Tick::ZERO, Default::default());
+    assert_ne!(img.data, plain.data, "the out-of-focus layer should have blurred");
+}
+
+/// Set Focus Distance to Layer fails cleanly on a depth that isn't finite. Every stored number
+/// here is finite, but their difference overflows f64 to infinity; JSON has no infinity, so
+/// storing it would leave a project that can't be saved.
+#[test]
+fn camera_set_focus_to_layer_rejects_non_finite_depth() {
+    let mut s = comp(400, 300);
+    let t = s.execute("layer.newSolid", json!({"color": "#ffffff", "width": 50, "height": 50})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.setSwitch", json!({"layers": [t], "switch": "threeD", "value": true})).unwrap();
+    s.execute("layer.setTransform", json!({"layer": t, "prop": "position", "value": [200.0, 150.0, 1e308]})).unwrap();
+    let cam = s.execute("layer.newCamera", json!({})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("layer.setTransform", json!({"layer": cam, "prop": "position", "value": [200.0, 150.0, -1e308]})).unwrap();
+    s.execute("layer.select", json!({"layers": [cam, t]})).unwrap();
+    let before = s.execute("prop.get", json!({"layer": cam, "path": "cameraOptions/focusDistance"})).unwrap()["value"].as_f64().unwrap();
+    let e = s.execute("camera.setFocusToLayer", json!({})).unwrap_err().to_string();
+    assert!(e.contains("out of range"), "{e}");
+    let after = s.execute("prop.get", json!({"layer": cam, "path": "cameraOptions/focusDistance"})).unwrap()["value"].as_f64().unwrap();
+    assert!((after - before).abs() < 1e-9, "a non-finite focus distance was written: {after}");
+    // The project still round-trips through serde (a stored infinity would come back as null).
+    let back = roundtrip(&s);
+    let f = back.comp(s.active_comp_id().unwrap()).unwrap().layer(LayerId(cam)).unwrap().props.prop("cameraOptions/focusDistance").unwrap().value.as_f64();
+    assert!((f - before).abs() < 1e-9, "serde focus distance: {f}");
+}
+
 /// An id sent as a string (`"98"`, as MCP clients often do) resolves as an id when no name matches.
 #[test]
 fn numeric_string_resolves_as_id() {
diff --git a/crates/gpu/src/bokeh.rs b/crates/gpu/src/bokeh.rs
index ac07448c9..9150fa6b4 100644
--- a/crates/gpu/src/bokeh.rs
+++ b/crates/gpu/src/bokeh.rs
@@ -10,8 +10,9 @@ use crate::context::{Enc, GpuImage, Params};
 
 /// Blur `src` (an unpadded plane buffer) as `d` says. Returns the padded, blurred image.
 pub(crate) fn apply(e: &mut Enc, src: &GpuImage, d: &PlaneDof) -> Option<GpuImage> {
-    let (w, h) = (src.width + 2 * d.pad, src.height + 2 * d.pad);
-    if !e.g.fits(w + 1, h) || d.radius.len() != w as usize * h as usize || d.levels.is_empty() {
+    // Saturating, so an oversized padding is refused by `fits` below instead of wrapping around.
+    let (w, h) = (src.width.saturating_add(d.pad.saturating_mul(2)), src.height.saturating_add(d.pad.saturating_mul(2)));
+    if !e.g.fits(w.saturating_add(1), h) || d.radius.len() != w as usize * h as usize || d.levels.is_empty() {
         return None;
     }
     let padded = e.image(w, h);
diff --git a/crates/raster/src/lib.rs b/crates/raster/src/lib.rs
index f17602829..c01b3d3c2 100644
--- a/crates/raster/src/lib.rs
+++ b/crates/raster/src/lib.rs
@@ -138,9 +138,11 @@ impl Image {
         }
         o
     }
-    /// Copy with `pad` transparent pixels on every side.
+    /// Copy with `pad` transparent pixels on every side. Sizes saturate rather than wrap around,
+    /// but a saturated size can't be allocated: callers bound `pad`.
     pub fn padded(&self, pad: u32) -> Image {
-        let mut out = Image::new(self.width + 2 * pad, self.height + 2 * pad);
+        let (w, h) = (self.width.saturating_add(pad.saturating_mul(2)), self.height.saturating_add(pad.saturating_mul(2)));
+        let mut out = Image::new(w, h);
         let ow = out.width as usize;
         for y in 0..self.height as usize {
             let src = &self.data[y * self.width as usize..(y + 1) * self.width as usize];
diff --git a/crates/render/src/three_d/camera.rs b/crates/render/src/three_d/camera.rs
index 5e1f983b2..bfdc4fb7b 100644
--- a/crates/render/src/three_d/camera.rs
+++ b/crates/render/src/three_d/camera.rs
@@ -37,7 +37,8 @@ pub struct Dof {
 impl Dof {
     /// Circle-of-confusion diameter (comp pixels) for a point at camera depth `z`.
     pub fn coc(&self, z: f64) -> f64 {
-        if z <= NEAR || self.focus <= 0.0 {
+        // No defocus can be measured against a non-finite focus or depth, so it counts as in focus.
+        if !z.is_finite() || z <= NEAR || !self.focus.is_finite() || self.focus <= 0.0 {
             return 0.0;
         }
         self.aperture * (z - self.focus).abs() / z * self.blur_level
@@ -313,22 +314,27 @@ pub fn layer_camera(ctx: &EvalCtx, cam: &Layer) -> CameraState {
     let (eye, fwd, down) = layer_frame(ctx, cam);
     let opts = cam.props.sub("cameraOptions");
     let zoom = opts.map(|g| ctx.f(cam, g, "zoom", 1000.0)).unwrap_or(1000.0).max(1e-3);
-    let dof = opts.filter(|g| ctx.b(cam, g, "dof")).map(|g| Dof {
-        focus: ctx.f(cam, g, "focusDistance", zoom),
-        aperture: ctx.f(cam, g, "aperture", default_aperture(w)).max(0.0),
-        blur_level: ctx.f(cam, g, "blurLevel", 100.0).max(0.0) / 100.0,
-        iris: super::bokeh::Iris {
-            sides: super::bokeh::Iris::sides_of_shape(ctx.e(cam, g, "irisShape")),
-            rotation: ctx.f(cam, g, "irisRotation", 0.0),
-            roundness: ctx.f(cam, g, "irisRoundness", 0.0) / 100.0,
-            aspect: ctx.f(cam, g, "irisAspectRatio", 1.0).max(0.01),
-            fringe: ctx.f(cam, g, "irisDiffractionFringe", 0.0).max(0.0) / 100.0,
-        },
-        highlight: super::bokeh::Highlight {
-            gain: ctx.f(cam, g, "highlightGain", 0.0).clamp(0.0, 100.0) / 100.0,
-            threshold: ctx.f(cam, g, "highlightThreshold", 255.0).clamp(0.0, 255.0) / 255.0,
-            saturation: ctx.f(cam, g, "highlightSaturation", 0.0).clamp(0.0, 100.0) / 100.0,
-        },
+    let dof = opts.filter(|g| ctx.b(cam, g, "dof")).map(|g| {
+        // A non-finite Focus Distance would make every blur radius non-finite; use the value the
+        // property defaults to (the zoom plane) instead.
+        let focus = ctx.f(cam, g, "focusDistance", zoom);
+        Dof {
+            focus: if focus.is_finite() { focus } else { zoom },
+            aperture: ctx.f(cam, g, "aperture", default_aperture(w)).max(0.0),
+            blur_level: ctx.f(cam, g, "blurLevel", 100.0).max(0.0) / 100.0,
+            iris: super::bokeh::Iris {
+                sides: super::bokeh::Iris::sides_of_shape(ctx.e(cam, g, "irisShape")),
+                rotation: ctx.f(cam, g, "irisRotation", 0.0),
+                roundness: ctx.f(cam, g, "irisRoundness", 0.0) / 100.0,
+                aspect: ctx.f(cam, g, "irisAspectRatio", 1.0).max(0.01),
+                fringe: ctx.f(cam, g, "irisDiffractionFringe", 0.0).max(0.0) / 100.0,
+            },
+            highlight: super::bokeh::Highlight {
+                gain: ctx.f(cam, g, "highlightGain", 0.0).clamp(0.0, 100.0) / 100.0,
+                threshold: ctx.f(cam, g, "highlightThreshold", 255.0).clamp(0.0, 255.0) / 255.0,
+                saturation: ctx.f(cam, g, "highlightSaturation", 0.0).clamp(0.0, 100.0) / 100.0,
+            },
+        }
     });
     CameraState { view: basis_view(eye, fwd, down), eye, zoom, ortho: false, dof }
 }
diff --git a/crates/render/src/three_d/compose.rs b/crates/render/src/three_d/compose.rs
index 6cf87e70e..416eada08 100644
--- a/crates/render/src/three_d/compose.rs
+++ b/crates/render/src/three_d/compose.rs
@@ -18,7 +18,7 @@ use std::sync::Arc;
 use effectcraft_color::{BlendMode, blend_pixel};
 use effectcraft_effects::Buf;
 use effectcraft_geom::{Mat3, Mat4, Vec3, vec3};
-use effectcraft_project::{Layer, LightKind, MatteKind};
+use effectcraft_project::{Layer, LightKind, MatteKind, limits};
 use effectcraft_raster::{Image, Px, hash_noise};
 use effectcraft_time::Tick;
 use rayon::prelude::*;
@@ -290,12 +290,43 @@ fn prepare_with<'a>(
 }
 
 /// Blur radius (buffer pixels) of every buffer pixel of a plane at `world` (layer → world), from
-/// its camera depth: the circle of confusion over the on-screen size of one layer pixel there.
-fn dof_radii(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, buf: &Buf) -> Vec<f32> {
-    dof_radii_at(cam, dof, world, (buf.img.width as usize, buf.img.height as usize), buf.offset, buf.scale)
+/// its camera depth: the circle of confusion over the on-screen size of one layer pixel there, at
+/// most `cap` ([`dof_radius_cap`]).
+fn dof_radii(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, buf: &Buf, cap: f64) -> Vec<f32> {
+    dof_radii_at(cam, dof, world, (buf.img.width as usize, buf.img.height as usize), buf.offset, buf.scale, cap)
 }
 
-fn dof_radii_at(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, (w, h): (usize, usize), offset: [f64; 2], scale: f64) -> Vec<f32> {
+/// Pixels a padded blur buffer may have: the ~16 million layer buffers are held to
+/// ([`crate::Renderer::raster_scale`]), so a blur never needs more memory than a large layer;
+/// twice the buffer when that is larger, so a big buffer can still be blurred.
+const DOF_PAD_BUDGET: f64 = 16.0e6;
+
+/// Comp pixels per buffer pixel below which a plane isn't blurred. Such a plane covers almost no
+/// screen area (a 0%-scaled layer, one at an extreme distance), while its radius in buffer
+/// pixels grows without bound as it shrinks: blurring it would cost the most for the least.
+const DOF_MIN_SCREEN_SCALE: f64 = 1e-3;
+
+/// The largest blur radius (buffer pixels) of a `w`×`h` buffer: the one whose padded copy just
+/// fits [`DOF_PAD_BUDGET`]. The circle of confusion has no bound of its own (a focus distance far
+/// beyond the scene, a near-zero layer scale), so memory sets the limit; ordinary bokeh stays far
+/// below it and is never clamped.
+pub(super) fn dof_radius_cap(dof: &super::camera::Dof, w: u32, h: u32) -> f64 {
+    let (w, h) = (w as f64, h as f64);
+    let budget = DOF_PAD_BUDGET.max(2.0 * w * h);
+    // (w + 2p)·(h + 2p) = budget, solved for the padding p.
+    let pad = (((w - h) * (w - h) + 4.0 * budget).sqrt() - (w + h)) / 4.0;
+    ((pad - 2.0) / iris_stretch(dof)).max(0.0)
+}
+
+pub(super) fn dof_radii_at(
+    cam: &CameraState,
+    dof: &super::camera::Dof,
+    world: Mat4,
+    (w, h): (usize, usize),
+    offset: [f64; 2],
+    scale: f64,
+    cap: f64,
+) -> Vec<f32> {
     let s = scale.max(1e-9);
     let sx = world.apply_vec(vec3(1.0, 0.0, 0.0)).length().max(1e-9);
     let at = |x: f64, y: f64| cam.depth(world.apply(vec3((x - offset[0]) / s, (y - offset[1]) / s, 0.0)));
@@ -309,31 +340,48 @@ fn dof_radii_at(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, (w, h)
             if z <= super::camera::NEAR {
                 continue;
             }
-            // coc · ½ / (zoom / z · sx) · scale
-            *o = (dof.coc(z) * 0.5 * z / (cam.zoom * sx) * s) as f32;
+            // coc · ½ / (zoom / z · sx) · scale. Infinity clamps to the cap like any large radius,
+            // so the blur keeps growing with defocus; only NaN, which has no defocus, stays sharp.
+            let r = dof.coc(z) * 0.5 * z / (cam.zoom * sx) * s;
+            *o = if r.is_nan() || cam.zoom * sx / (z * s) < DOF_MIN_SCREEN_SCALE { 0.0 } else { r.min(cap) as f32 };
         }
     });
     out
 }
 
+/// How much the iris' aspect ratio stretches a blur radius along its longer axis.
+fn iris_stretch(dof: &super::camera::Dof) -> f64 {
+    let a = dof.iris.aspect.clamp(0.01, 100.0).sqrt();
+    a.max(1.0 / a)
+}
+
 /// The padding [`dof_blur`] gives a buffer whose largest blur radius is `rmax`.
 fn dof_pad(dof: &super::camera::Dof, rmax: f64) -> u32 {
-    let a = dof.iris.aspect.clamp(0.01, 100.0).sqrt().max(1.0 / dof.iris.aspect.clamp(0.01, 100.0).sqrt());
-    (rmax * a).ceil() as u32 + 2
+    ((rmax * iris_stretch(dof)).ceil() as u32).saturating_add(2)
+}
+
+/// The size of `img` padded by `pad` on every side, or `None` past [`limits::MAX_SIZE`] on a side:
+/// [`DOF_PAD_BUDGET`] bounds the area, so a long thin buffer could still outgrow a side.
+fn padded_size(img: &Image, pad: u32) -> Option<(u32, u32)> {
+    let grow = |n: u32| n.saturating_add(pad.saturating_mul(2));
+    let (w, h) = (grow(img.width), grow(img.height));
+    (w <= limits::MAX_SIZE && h <= limits::MAX_SIZE).then_some((w, h))
 }
 
 /// [`dof_blur`] planned for an accelerator: the padding, radius map and levels, and the padded
 /// buffer's layer-space bounds. `None` when nothing blurs.
 fn dof_plan(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, buf: &Buf) -> Option<(PlaneDof, [f64; 4])> {
-    let radii = dof_radii(cam, dof, world, buf);
+    let cap = dof_radius_cap(dof, buf.img.width, buf.img.height);
+    let radii = dof_radii(cam, dof, world, buf, cap);
     let rmax = radii.iter().copied().fold(0.0f32, f32::max) as f64;
     if rmax <= 0.3 {
         return None;
     }
     let pad = dof_pad(dof, rmax);
-    let (w, h) = (buf.img.width as usize + 2 * pad as usize, buf.img.height as usize + 2 * pad as usize);
+    let (wp, hp) = padded_size(&buf.img, pad)?;
+    let (w, h) = (wp as usize, hp as usize);
     let offset = [buf.offset[0] + pad as f64, buf.offset[1] + pad as f64];
-    let radius = dof_radii_at(cam, dof, world, (w, h), offset, buf.scale);
+    let radius = dof_radii_at(cam, dof, world, (w, h), offset, buf.scale, cap);
     let levels = super::bokeh::blur_levels(&radius)?;
     let s = buf.scale.max(1e-9);
     let bounds = [-offset[0] / s, -offset[1] / s, (w as f64 - offset[0]) / s, (h as f64 - offset[1]) / s];
@@ -342,16 +390,20 @@ fn dof_plan(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, buf: &Buf)
 
 /// Depth of field for one plane: highlights boosted, then a bokeh-shaped blur by depth.
 fn dof_blur(cam: &CameraState, dof: &super::camera::Dof, world: Mat4, buf: Arc<Buf>) -> Arc<Buf> {
-    let radii = dof_radii(cam, dof, world, &buf);
+    let cap = dof_radius_cap(dof, buf.img.width, buf.img.height);
+    let radii = dof_radii(cam, dof, world, &buf, cap);
     let rmax = radii.iter().copied().fold(0.0f32, f32::max) as f64;
     if rmax <= 0.3 {
         return buf;
     }
     let pad = dof_pad(dof, rmax);
+    if padded_size(&buf.img, pad).is_none() {
+        return buf;
+    }
     let mut padded = buf.img.padded(pad);
     super::bokeh::boost_highlights(&mut padded, &dof.highlight);
     let pbuf = Buf { img: padded, offset: [buf.offset[0] + pad as f64, buf.offset[1] + pad as f64], scale: buf.scale };
-    let pr = dof_radii(cam, dof, world, &pbuf);
+    let pr = dof_radii(cam, dof, world, &pbuf, cap);
     // The (cached, shared) layer buffer stays untouched; the blurred copy is per frame.
     Arc::new(Buf { img: super::bokeh::progressive_blur(&pbuf.img, &dof.iris, &pr), offset: pbuf.offset, scale: pbuf.scale })
 }
diff --git a/crates/render/src/three_d/tests.rs b/crates/render/src/three_d/tests.rs
index 9f1dbb344..ecaaa4d9a 100644
--- a/crates/render/src/three_d/tests.rs
+++ b/crates/render/src/three_d/tests.rs
@@ -13,10 +13,15 @@ const W: u32 = 200;
 const H: u32 = 100;
 
 fn setup() -> (Project, ItemId, Comp) {
+    setup_sized(W, H)
+}
+
+/// [`setup`] with a `w`×`h` comp.
+fn setup_sized(w: u32, h: u32) -> (Project, ItemId, Comp) {
     let mut p = Project::default();
     // Exact float maths; 8/16 bpc quantisation has its own tests (tests_color).
     p.settings.bit_depth = effectcraft_project::BitDepth::Bpc32;
-    let comp = Comp::new(W, H, FrameRate::FPS_30, Tick::from_seconds_f64(2.0));
+    let comp = Comp::new(w, h, FrameRate::FPS_30, Tick::from_seconds_f64(2.0));
     let cid = p.add_item("Comp", Label::Sandstone, None, ItemKind::Comp(comp.clone().into()));
     (p, cid, comp)
 }
@@ -347,7 +352,7 @@ fn shadow_darkness_and_accepts_off() {
 // ---------------------------------------------------------------- cameras
 
 fn camera(p: &mut Project, comp: &Comp) -> Layer {
-    build::layer(p, comp, "Camera", LayerSource::Camera, (W, H), None)
+    build::layer(p, comp, "Camera", LayerSource::Camera, (comp.width, comp.height), None)
 }
 
 #[test]
@@ -423,9 +428,155 @@ fn depth_of_field_blurs_out_of_focus_layers() {
     assert!(b.get(66, 50)[3] > 0.01);
 }
 
+/// A non-finite Focus Distance doesn't reach the blur: the camera focuses on the property's
+/// default plane (`zoom`) instead.
+#[test]
+fn dof_falls_back_when_focus_distance_is_not_finite() {
+    for bad in [f64::NAN, f64::INFINITY, f64::NEG_INFINITY] {
+        let (mut p, cid, comp) = setup();
+        let mut cam = camera(&mut p, &comp);
+        set(&mut cam, "cameraOptions/dof", Value::Bool(true));
+        set(&mut cam, "cameraOptions/aperture", Value::Scalar(60.0));
+        set(&mut cam, "cameraOptions/focusDistance", Value::Scalar(bad));
+        let s = solid3(&mut p, &comp, [1.0, 1.0, 1.0], 60, 60, [100.0, 50.0, 0.0]);
+        push(&mut p, cid, cam);
+        push(&mut p, cid, s);
+        let cp = p.comp(cid).unwrap();
+        let ctx = crate::EvalCtx::new(&p, cid, cp, Tick::ZERO);
+        let cs = crate::three_d::camera::layer_camera(&ctx, &cp.layers[0]);
+        let f = cs.dof.unwrap().focus;
+        assert!((f - zoom()).abs() < 1e-9, "{bad}: evaluated to {f}, expected the fallback to zoom {}", zoom());
+        // The z = 0 plane is in focus: hard edge, finite pixels.
+        let img = render(&p, cid);
+        assert!(img.get(71, 50)[3] > 0.99 && img.get(69, 50)[3] < 0.01, "{bad}: the edge should be hard");
+        assert!(img.data.iter().all(|px| px.iter().all(|c| c.is_finite())), "{bad}: non-finite pixels");
+    }
+}
+
+/// The Classic 3D blur stays bounded for degenerate inputs: a 0%-scaled 3D layer off the focal
+/// plane (e.g. the first frame of a scale-in) or a huge but finite Focus Distance asks for a
+/// radius of billions of buffer pixels, whose padded buffer can't be allocated.
+#[test]
+fn dof_blur_radius_is_bounded_for_degenerate_inputs() {
+    let scene = |focus: f64, scale: f64| {
+        let (mut p, cid, comp) = setup();
+        let mut cam = camera(&mut p, &comp);
+        set(&mut cam, "cameraOptions/dof", Value::Bool(true));
+        set(&mut cam, "cameraOptions/aperture", Value::Scalar(60.0));
+        set(&mut cam, "cameraOptions/focusDistance", Value::Scalar(focus));
+        let mut s = solid3(&mut p, &comp, [1.0, 1.0, 1.0], 60, 60, [100.0, 50.0, 0.0]);
+        set(&mut s, "transform/scale", Value::Vec3([scale, scale, 100.0]));
+        push(&mut p, cid, cam);
+        push(&mut p, cid, s);
+        render(&p, cid)
+    };
+    let finite = |img: &effectcraft_raster::Image| img.data.iter().all(|px| px.iter().all(|c| c.is_finite()));
+    // A 0%-scaled layer 10 px off the focal plane: an ordinary defocus times 1/sx (sx = 1e-9).
+    assert!(finite(&scene(zoom() + 10.0, 0.0)), "zero-scaled: non-finite pixels");
+    // Huge but finite Focus Distances (typed in, or a large expression result): the blur is as
+    // large as the buffer budget allows, never refused (which would render the layer sharp).
+    // 1e307 overflows the circle of confusion itself to infinity: still the largest blur.
+    for focus in [1.0e12, 1.0e307] {
+        let img = scene(focus, 100.0);
+        assert!(finite(&img), "focus {focus:e}: non-finite pixels");
+        assert!(img.get(100, 50)[3] < 0.5, "focus {focus:e}: the layer should be spread out, not sharp ({})", img.get(100, 50)[3]);
+    }
+}
+
+/// The blur radius map of a plane: a 0%-scaled plane is degenerate on screen and isn't blurred;
+/// any other radius stays within the buffer budget's cap.
+#[test]
+fn dof_radii_skip_degenerate_planes_and_respect_the_cap() {
+    let radii = |focus: f64, scale: f64| {
+        let (mut p, cid, comp) = setup();
+        let mut cam = camera(&mut p, &comp);
+        set(&mut cam, "cameraOptions/dof", Value::Bool(true));
+        set(&mut cam, "cameraOptions/aperture", Value::Scalar(60.0));
+        set(&mut cam, "cameraOptions/focusDistance", Value::Scalar(focus));
+        let mut s = solid3(&mut p, &comp, [1.0, 1.0, 1.0], 60, 60, [100.0, 50.0, 0.0]);
+        set(&mut s, "transform/scale", Value::Vec3([scale, scale, 100.0]));
+        push(&mut p, cid, cam);
+        push(&mut p, cid, s);
+        let cp = p.comp(cid).unwrap();
+        let ctx = crate::EvalCtx::new(&p, cid, cp, Tick::ZERO);
+        let cs = super::camera::layer_camera(&ctx, &cp.layers[0]);
+        let dof = cs.dof.unwrap();
+        let cap = super::compose::dof_radius_cap(&dof, 60, 60);
+        (super::compose::dof_radii_at(&cs, &dof, ctx.world_matrix(&cp.layers[1]), (60, 60), [0.0; 2], 1.0, cap), cap)
+    };
+    let (r, _) = radii(zoom() + 10.0, 0.0);
+    assert!(r.iter().all(|&r| r == 0.0), "a 0%-scaled plane is not blurred");
+    let (r, cap) = radii(1.0e12, 100.0);
+    assert!(cap > 1000.0, "a 60×60 buffer may blur by well over 1000 px: {cap}");
+    assert!(r.iter().all(|&r| r as f64 <= cap && r as f64 > cap - 1.0), "huge focus: every radius at the cap {cap}");
+}
+
+/// Two layers that look the same on screen (400×100 at 100%, 1600×400 at 25%) at the same depth
+/// blur by the same amount on screen: the radius bound must not depend on the layer's scale.
+#[test]
+fn dof_blur_is_independent_of_layer_scale() {
+    let ramp = |w: u32, h: u32, scale: f64| {
+        let (mut p, cid, comp) = setup_sized(800, 400);
+        let zoom = 800.0 * 50.0 / 36.0;
+        let mut cam = camera(&mut p, &comp);
+        set(&mut cam, "cameraOptions/dof", Value::Bool(true));
+        set(&mut cam, "cameraOptions/aperture", Value::Scalar(200.0));
+        // coc = aperture·|z − f| / z: a 40 px comp radius on the z = 0 plane (depth = zoom).
+        set(&mut cam, "cameraOptions/focusDistance", Value::Scalar(zoom + 2.0 * 40.0 * zoom / 200.0));
+        let mut s = solid3(&mut p, &comp, [1.0, 1.0, 1.0], w, h, [400.0, 200.0, 0.0]);
+        set(&mut s, "transform/scale", Value::Vec3([scale, scale, 100.0]));
+        push(&mut p, cid, cam);
+        push(&mut p, cid, s);
+        let img = render(&p, cid);
+        soft_count(&img, (0..400).map(|x| (x, 200)))
+    };
+    let (full, quarter) = (ramp(400, 100, 100.0), ramp(1600, 400, 25.0));
+    assert!(full > 60, "the out-of-focus edge should be soft: {full}");
+    assert!(full.abs_diff(quarter) <= 2, "same on-screen layer, same depth: {full} px at 100% vs {quarter} px at 25%");
+}
+
+/// The same frame at Full and Half resolution shows the same blur (in comp pixels). The radius
+/// (~100 px) is large so that any bound that depends on the resolution would show.
+#[test]
+fn dof_blur_matches_across_render_resolutions() {
+    let (mut p, cid, comp) = setup_sized(800, 400);
+    let zoom = 800.0 * 50.0 / 36.0;
+    let mut cam = camera(&mut p, &comp);
+    set(&mut cam, "cameraOptions/dof", Value::Bool(true));
+    set(&mut cam, "cameraOptions/aperture", Value::Scalar(200.0));
+    set(&mut cam, "cameraOptions/focusDistance", Value::Scalar(2.0 * zoom));
+    let s = solid3(&mut p, &comp, [1.0, 1.0, 1.0], 400, 100, [400.0, 200.0, 0.0]);
+    push(&mut p, cid, cam);
+    push(&mut p, cid, s);
+    let ramp = |scale: f64| {
+        let img = render_frame(&p, cid, Tick::ZERO, scale);
+        let (w, h) = (img.width as i64, img.height as i64);
+        soft_count(&img, (0..w / 2).map(|x| (x, h / 2))) as f64 / scale
+    };
+    let (full, half) = (ramp(1.0), ramp(0.5));
+    assert!(full > 150.0, "a ~100 px radius must not be clamped: {full} comp px");
+    assert!((full - half).abs() <= 4.0, "Full {full} vs Half {half} comp px");
+}
+
+/// `Dof::coc` treats a non-finite focus or depth as in focus.
+#[test]
+fn dof_coc_is_zero_for_non_finite_inputs() {
+    let d = |focus: f64| super::camera::Dof { focus, aperture: 50.0, blur_level: 1.0, iris: Default::default(), highlight: Default::default() };
+    for bad in [f64::NAN, f64::INFINITY, f64::NEG_INFINITY] {
+        assert_eq!(d(bad).coc(500.0), 0.0, "focus {bad}");
+        assert_eq!(d(400.0).coc(bad), 0.0, "depth {bad}");
+    }
+    assert!(d(400.0).coc(500.0) > 0.0);
+}
+
+/// Pixels among `pts` whose alpha is strictly between 0.05 and 0.95.
+fn soft_count(img: &effectcraft_raster::Image, pts: impl Iterator<Item = (i64, i64)>) -> usize {
+    pts.filter(|&(x, y)| (0.05..0.95).contains(&img.get(x, y)[3])).count()
+}
+
 /// Pixels in column `x` whose alpha is strictly between 0.05 and 0.95.
 fn soft_px(img: &effectcraft_raster::Image, x: i64) -> usize {
-    (0..img.height as i64).filter(|&y| (0.05..0.95).contains(&img.get(x, y)[3])).count()
+    soft_count(img, (0..img.height as i64).map(|y| (x, y)))
 }
 
 #[test]