A Unity Editor utility for cameras with extremely low FOV.

LowFovCameraUtilityEditor.cs

using UnityEngine;
using UnityEditor;
using Cinemachine;
using System.Collections.Generic;

// To make this work, create an empty MonoBehaviour called "LowFovCameraUtility".
// Then, attach that script to your Cinemachine virtual cameras.
// If you don't want to use Cinemachine virtual cameras this script should work too,
// you'll just need to modify the components and variable names.
[CustomEditor(typeof(LowFovCameraUtility))]
public class LowFovCameraUtilityEditor : Editor
{
    // This is the amount of depth/height the near/far plane will allow for when automatically set.
    public static float nearPlaneFudge = 30f;
    public static float farPlaneFudge = 30f;

    private CinemachineVirtualCamera camera;
    private SerializedObject serializedCinemachineVcam;
    private SerializedProperty cinemachineVcamNearClipProperty;
    private SerializedProperty cinemachineVcamFarClipProperty;

    private void OnEnable()
    {
        LowFovCameraUtility target = this.target as LowFovCameraUtility;
        camera = target.GetComponent<CinemachineVirtualCamera>();
        if (camera == null)
        {
            Debug.LogError("No camera attached", target);
        }

        serializedCinemachineVcam = new SerializedObject(camera);
        cinemachineVcamNearClipProperty = serializedCinemachineVcam.FindProperty("m_Lens").FindPropertyRelative("NearClipPlane");
        cinemachineVcamFarClipProperty = serializedCinemachineVcam.FindProperty("m_Lens").FindPropertyRelative("FarClipPlane");
    }

    private void OnSceneGUI()
    {
        if (target == null)
        {
            return;
        }

        if (camera == null)
        {
            Debug.LogError("No camera attached", target);
            return;
        }

        Vector3 handlePosition = camera.transform.position + camera.transform.forward * camera.m_Lens.NearClipPlane;
        Vector3 newPosition = handlePosition;
        Quaternion newRotation = camera.transform.rotation;

        switch (Tools.current)
        {
            case Tool.Move:
                newPosition = Handles.DoPositionHandle(handlePosition, Tools.handleRotation);
                if ((newPosition - handlePosition).sqrMagnitude > Mathf.Epsilon)
                {
                    Undo.RecordObject(camera.transform, "Low Fov Camera Utility Handle Move");
                    camera.transform.position += (newPosition - handlePosition);
                }
                break;
            case Tool.Rotate:
                newRotation = Handles.DoRotationHandle(camera.transform.rotation, handlePosition);
                if (Quaternion.Angle(newRotation, camera.transform.rotation) > Mathf.Epsilon)
                {
                    Undo.RecordObject(camera.transform, "Low Fov Camera Utility Handle Rotate");
                    camera.transform.rotation = newRotation;
                    camera.transform.position = handlePosition - newRotation * (Vector3.forward * Vector3.Distance(camera.transform.position, handlePosition));
                }
                break;
            default:
                break;
        }
    }

    public override void OnInspectorGUI()
    {
        serializedObject.Update();

        DrawDefaultInspector();

        if (GUILayout.Button("Auto-resize clip planes"))
        {
            SetCameraProps(target as LowFovCameraUtility);
            serializedCinemachineVcam.ApplyModifiedProperties();
        }

        serializedObject.ApplyModifiedProperties();
    }

    public void SetCameraProps(LowFovCameraUtility target)
    {
        float theta = Vector3.Angle(camera.transform.forward, Vector3.down);
        float y = camera.transform.position.y;

        float topPlaneDistanceToZero = (y + farPlaneFudge) / Mathf.Cos((theta + camera.m_Lens.FieldOfView / 2f) * Mathf.Deg2Rad);
        float farPlaneDistance = Mathf.Cos(camera.m_Lens.FieldOfView / 2f * Mathf.Deg2Rad) * topPlaneDistanceToZero;

        float bottomPlaneDistanceToZero = (y - nearPlaneFudge) / Mathf.Cos((theta - camera.m_Lens.FieldOfView / 2f) * Mathf.Deg2Rad);
        float nearPlaneDistance = Mathf.Cos(camera.m_Lens.FieldOfView / 2f * Mathf.Deg2Rad) * bottomPlaneDistanceToZero;

        cinemachineVcamNearClipProperty.floatValue = nearPlaneDistance;
        cinemachineVcamFarClipProperty.floatValue = farPlaneDistance;
    }
}