diff --git a/docs/source/examples/3d.rst b/docs/source/examples/3d.rst
index 9c25ab6642..90d7ef4cba 100644
--- a/docs/source/examples/3d.rst
+++ b/docs/source/examples/3d.rst
@@ -1,5 +1,18 @@
+
 3D Scenes
 =================================
+.. manim:: FixedInFrameMObjectTest
+    :save_last_frame:
+    class FixedInFrameMObjectTest(ThreeDScene):
+        def construct(self):
+            axes = ThreeDAxes()
+            self.set_camera_orientation(phi=75 * DEGREES, theta=-45 * DEGREES)
+            text3d = Text("This is a 3D text")
+            self.add_fixed_in_frame_mobjects(text3d)
+            text3d.to_corner(UL)
+            self.add(axes)
+            self.wait()
+
 
 .. manim:: ThreeDSphere
     :save_last_frame:
diff --git a/manim/camera/camera.py b/manim/camera/camera.py
index 84bbdc50e3..9835f4a411 100644
--- a/manim/camera/camera.py
+++ b/manim/camera/camera.py
@@ -3,7 +3,7 @@
 
 __all__ = ["Camera", "BackgroundColoredVMobjectDisplayer"]
 
-
+from functools import reduce
 import itertools as it
 import operator as op
 import time
@@ -1039,7 +1039,7 @@ def adjusted_thickness(self, thickness):
 
         """
         # TODO: This seems...unsystematic
-        big_sum = op.add(config["default_pixel_height"], config["default_pixel_width"])
+        big_sum = op.add(config["pixel_height"], config["pixel_width"])
         this_sum = op.add(self.pixel_height, self.pixel_width)
         factor = fdiv(big_sum, this_sum)
         return 1 + (thickness - 1) / factor
diff --git a/manim/camera/three_d_camera.py b/manim/camera/three_d_camera.py
index 55271aeeb3..0385369881 100644
--- a/manim/camera/three_d_camera.py
+++ b/manim/camera/three_d_camera.py
@@ -18,6 +18,7 @@
 from ..utils.simple_functions import clip_in_place
 from ..utils.space_ops import rotation_about_z
 from ..utils.space_ops import rotation_matrix
+from ..utils.family import extract_mobject_family_members
 
 
 class ThreeDCamera(Camera):
@@ -367,7 +368,7 @@ def add_fixed_in_frame_mobjects(self, *mobjects):
         **mobjects : Mobject
             The mobject to fix in frame.
         """
-        for mobject in self.extract_mobject_family_members(mobjects):
+        for mobject in extract_mobject_family_members(mobjects):
             self.fixed_in_frame_mobjects.add(mobject)
 
     def remove_fixed_orientation_mobjects(self, *mobjects):
diff --git a/manim/scene/three_d_scene.py b/manim/scene/three_d_scene.py
index 5065899f5d..f35ee0a477 100644
--- a/manim/scene/three_d_scene.py
+++ b/manim/scene/three_d_scene.py
@@ -165,7 +165,7 @@ def move_camera(
                 anims.append(ApplyMethod(tracker.set_value, value, **kwargs))
         if frame_center is not None:
             anims.append(
-                ApplyMethod(self.renderer.camera.frame_center.move_to, frame_center)
+                ApplyMethod(self.renderer.camera._frame_center.move_to, frame_center)
             )
 
         self.play(*anims + added_anims)
diff --git a/tests/control_data/graphical_units_data/threed/CameraMoveTest.npz b/tests/control_data/graphical_units_data/threed/CameraMoveTest.npz
index 7c4dcd1979..4d7054c930 100644
Binary files a/tests/control_data/graphical_units_data/threed/CameraMoveTest.npz and b/tests/control_data/graphical_units_data/threed/CameraMoveTest.npz differ
diff --git a/tests/control_data/graphical_units_data/threed/FixedInFrameMObjectTest.npz b/tests/control_data/graphical_units_data/threed/FixedInFrameMObjectTest.npz
new file mode 100644
index 0000000000..c14f3c6101
Binary files /dev/null and b/tests/control_data/graphical_units_data/threed/FixedInFrameMObjectTest.npz differ
diff --git a/tests/test_graphical_units/test_threed.py b/tests/test_graphical_units/test_threed.py
index ce7cc8ae3f..8068a7323a 100644
--- a/tests/test_graphical_units/test_threed.py
+++ b/tests/test_graphical_units/test_threed.py
@@ -24,7 +24,7 @@ class CameraMoveTest(ThreeDScene):
     def construct(self):
         cube = Cube()
         self.play(Animation(cube))
-        self.move_camera(phi=PI / 4, theta=PI / 4)
+        self.move_camera(phi=PI / 4, theta=PI / 4, frame_center=[0, 0, -1])
 
 
 class AmbientCameraMoveTest(ThreeDScene):
@@ -34,6 +34,17 @@ def construct(self):
         self.play(Animation(cube))
 
 
+class FixedInFrameMObjectTest(ThreeDScene):
+    def construct(self):
+        axes = ThreeDAxes()
+        self.set_camera_orientation(phi=75 * DEGREES, theta=-45 * DEGREES)
+        circ = Circle()
+        self.add_fixed_in_frame_mobjects(circ)
+        circ.to_corner(UL)
+        self.add(axes)
+        self.wait()
+
+
 MODULE_NAME = "threed"