From c3a299d6645aa05508a6050e98b4729138b1e129 Mon Sep 17 00:00:00 2001
From: michealroberts <michael@observerly.com>
Date: Thu, 10 Oct 2024 09:01:58 +0100
Subject: [PATCH] feat: add getFocalRation() utility to optics module in
 @observerly/astrometry

feat: add getFocalRation() utility to optics module in @observerly/astrometry
---
 src/optics.ts | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/optics.ts b/src/optics.ts
index 703412d..bc13f21 100644
--- a/src/optics.ts
+++ b/src/optics.ts
@@ -6,6 +6,29 @@
 
 /*****************************************************************************************************************/
 
-export {}
+type FocalRatio = `f/${number}`
+
+/*****************************************************************************************************************/
+
+/**
+ *
+ * getFocalRatio()
+ *
+ * @param apertureWidth - the aperture of the optics
+ * @param focalLength - the focal length of the optics
+ * @returns the focal ratio as a string formatted in the standard focal ratio, e.g., f/x.
+ */
+export function getFocalRatio(apertureWidth: number, focalLength: number): FocalRatio {
+  // Check that the aperterure is a sensible number, e.g., > 0:
+  if (apertureWidth < 0) {
+    throw new Error(`Invalid focal ratio as aperture is negative`)
+  }
+
+  if (focalLength < 0) {
+    throw new Error(`Invalid focal ratio as focal length is negative`)
+  }
+
+  return `f/${focalLength / apertureWidth}`
+}
 
 /*****************************************************************************************************************/