fix: Allow negative EFLs by removing sign hack

crates/cherry-rs/src/examples/wf_epi_excitation.rs

@@ -21,6 +21,7 @@ use crate::{
 
 pub fn sequential_model(
     n_air: Rc<dyn RefractiveIndexSpec>,
+    n_oil: Rc<dyn RefractiveIndexSpec>,
     wavelengths: &[f64],
 ) -> SequentialModel {
     let gap_0 = GapSpec {
@@ -33,11 +34,11 @@ pub fn sequential_model(
     };
     let gap_2 = GapSpec {
         thickness: 50.0,
-        refractive_index: n_air.clone(),
+        refractive_index: n_air,
     };
     let gap_3 = GapSpec {
         thickness: 1.0,
-        refractive_index: n_air,
+        refractive_index: n_oil,
     };
     let gaps = vec![gap_0, gap_1, gap_2, gap_3];
 
@@ -50,7 +51,7 @@ pub fn sequential_model(
         rotation_offset: Rotation3D::None,
     };
     let surf_2 = SurfaceSpec::Conic {
-        semi_diameter: 23.2,
+        semi_diameter: 36.0,
         radius_of_curvature: Float::INFINITY,
         conic_constant: 0.0,
         surf_kind: BoundaryKind::Reflecting,
@@ -63,7 +64,7 @@ pub fn sequential_model(
         rotation_offset: Rotation3D::None,
     };
     let surf_3 = SurfaceSpec::ThinLens {
-        semi_diameter: 4.75,
+        semi_diameter: 4.25,
         focal_length: 3.3333,
         rotation: Rotation3D::None,
         decenter: Vec3::new(0.0, 0.0, 0.0),

crates/cherry-rs/src/views/paraxial.rs

@@ -836,17 +836,14 @@ impl ParaxialSubView {
         let y_1 = parallel_ray.rays_at_surface(1)[0].height;
         let u_final = parallel_ray.rays_at_surface(parallel_ray.num_surfaces() - 2)[0].angle;
 
-        // There should be a negative sign here for lens only systems, but we take abs
-        // later so it's not needed
-        let efl = y_1 / u_final;
+        let efl = -y_1 / u_final;
 
         // Handle edge case for negatively infinite EFL
         if efl.is_infinite() {
             return Float::INFINITY;
         }
 
-        // abs() handles edge case of apparent negative EFLs in reflecting systems
-        efl.abs()
+        efl
     }
 
     #[allow(clippy::too_many_arguments)]
@@ -918,7 +915,7 @@ impl ParaxialSubView {
 
         Ok(Pupil {
             location,
-            semi_diameter,
+            semi_diameter: semi_diameter.abs(), // semi-diameter is always positive
         })
     }
 

crates/cherry-rs/tests/wf_epi_excitation.rs

@@ -4,19 +4,71 @@ use cherry_rs::examples::wf_epi_excitation::sequential_model;
 use cherry_rs::{FieldSpec, ParaxialView, n};
 
 const WAVELENGTHS: [f64; 1] = [0.5876];
-const FIELD_SPECS: [FieldSpec; 1] = [FieldSpec::PointSource { x: 0.0, y: 0.0 }];
-
-// Hand calculation: the stop (second thin lens) is 150 mm (100 mm + 50 mm,
-// the fold mirror has no power) downstream of the first thin lens
-// (f = 40 mm). Treating the stop as a real object and solving the thin lens
-// equation 1/s' = 1/f - 1/s with s = 150 mm gives s' = 600/11 = 54.5455 mm,
-// with the resulting image (the entrance pupil) on the object-space side of
-// the first thin lens.
+const FIELD_SPECS: [FieldSpec; 1] = [FieldSpec::PointSource { x: 0.0, y: 1.5 }];
+
+// Paraxial property values
+const APERTURE_STOP: usize = 3;
+const BACK_FOCAL_DISTANCE: f64 = 5.1562;
+const BACK_PRINCIPAL_PLANE: f64 = 7.0312;
+const EFFECTIVE_FOCAL_LENGTH: f64 = -1.8750;
 const ENTRANCE_PUPIL_LOCATION: f64 = -54.5455;
+const ENTRANCE_PUPIL_SIZE: f64 = 1.5454;
+
+#[test]
+fn wf_epi_excitation_paraxial_aperture_stop() {
+    let model = sequential_model(n!(1.0), n!(1.5), &WAVELENGTHS);
+    let view =
+        ParaxialView::new(&model, &FIELD_SPECS, false).expect("Could not create paraxial view");
+
+    for sub_view in view.iter() {
+        let result = sub_view.aperture_stop();
+
+        assert_eq!(APERTURE_STOP, *result)
+    }
+}
+
+#[test]
+fn wf_epi_excitation_paraxial_back_principal_plane() {
+    let model = sequential_model(n!(1.0), n!(1.5), &WAVELENGTHS);
+    let view =
+        ParaxialView::new(&model, &FIELD_SPECS, false).expect("Could not create paraxial view");
+
+    for sub_view in view.iter() {
+        let result = sub_view.back_principal_plane();
+
+        assert_abs_diff_eq!(BACK_PRINCIPAL_PLANE, *result, epsilon = 1e-4)
+    }
+}
+
+#[test]
+fn wf_epi_excitation_paraxial_back_focal_distance() {
+    let model = sequential_model(n!(1.0), n!(1.5), &WAVELENGTHS);
+    let view =
+        ParaxialView::new(&model, &FIELD_SPECS, false).expect("Could not create paraxial view");
+
+    for sub_view in view.iter() {
+        let result = sub_view.back_focal_distance();
+
+        assert_abs_diff_eq!(BACK_FOCAL_DISTANCE, *result, epsilon = 1e-4)
+    }
+}
+
+#[test]
+fn wf_epi_excitation_paraxial_effective_focal_length() {
+    let model = sequential_model(n!(1.0), n!(1.5), &WAVELENGTHS);
+    let view =
+        ParaxialView::new(&model, &FIELD_SPECS, false).expect("Could not create paraxial view");
+
+    for sub_view in view.iter() {
+        let result = sub_view.effective_focal_length();
+
+        assert_abs_diff_eq!(EFFECTIVE_FOCAL_LENGTH, *result, epsilon = 1e-4)
+    }
+}
 
 #[test]
 fn wf_epi_excitation_entrance_pupil_location() {
-    let model = sequential_model(n!(1.0), &WAVELENGTHS);
+    let model = sequential_model(n!(1.0), n!(1.5), &WAVELENGTHS);
     let view =
         ParaxialView::new(&model, &FIELD_SPECS, false).expect("Could not create paraxial view");
 
@@ -27,5 +79,10 @@ fn wf_epi_excitation_entrance_pupil_location() {
             ENTRANCE_PUPIL_LOCATION,
             epsilon = 1e-3
         );
+        assert_abs_diff_eq!(
+            entrance_pupil.semi_diameter,
+            ENTRANCE_PUPIL_SIZE,
+            epsilon = 1e-3
+        );
     }
 }