diff --git a/src/ophyd_async/epics/areadetector/aravis.py b/src/ophyd_async/epics/areadetector/aravis.py
index a2edbed8b0..b6d2ab79f8 100644
--- a/src/ophyd_async/epics/areadetector/aravis.py
+++ b/src/ophyd_async/epics/areadetector/aravis.py
@@ -1,6 +1,7 @@
 from typing import get_args
 
 from bluesky.protocols import HasHints, Hints
+
 from ophyd_async.core import (
     DirectoryProvider,
     StandardDetector,
@@ -52,7 +53,7 @@ def __init__(
         )
 
     async def _prepare(self, value: TriggerInfo) -> None:
-        await self.drv._fetch_deadtime()
+        await self.drv.fetch_deadtime()
         await super()._prepare(value)
 
     def get_external_trigger_gpio(self):
diff --git a/src/ophyd_async/epics/areadetector/drivers/aravis_driver.py b/src/ophyd_async/epics/areadetector/drivers/aravis_driver.py
index 9b3a9fa6de..d083bf49f6 100644
--- a/src/ophyd_async/epics/areadetector/drivers/aravis_driver.py
+++ b/src/ophyd_async/epics/areadetector/drivers/aravis_driver.py
@@ -33,12 +33,14 @@ class ADAravisTriggerSource(str, Enum):
     line_4 = "Line4"
 
 
-def _reverse_lookup(model_deadtimes: Dict[float, Tuple[str, ...]]) -> Callable[[str], float]:
+def _reverse_lookup(
+    model_deadtimes: Dict[float, Tuple[str, ...]],
+) -> Callable[[str], float]:
     def inner(pixel_format: str) -> float:
         for deadtime, pixel_formats in model_deadtimes.items():
             if pixel_format in pixel_formats:
                 return deadtime
-        return nan
+        None
 
     return inner
 
@@ -150,8 +152,15 @@ def __init__(self, prefix: str, name: str = "") -> None:
         self.dead_time: Optional[float] = None
         super().__init__(prefix, name=name)
 
-    async def _fetch_deadtime(self) -> float:
+    async def fetch_deadtime(self) -> float:
         # All known in-use version B/C have same deadtime as non-B/C
         model: str = (await self.model.get_value()).removesuffix("B").removesuffix("C")
         pixel_format: str = await self.pixel_format.get_value()
-        self.dead_time = _deadtimes.get(model, lambda _: nan)(pixel_format)
+        if model not in _deadtimes:
+            raise ValueError(f"Aravis model {model} deadtimes not known")
+        deadtime = _deadtimes[model](pixel_format)
+        if deadtime is None:
+            raise ValueError(
+                f"Aravis model {model} deadtime not known for pixel_format {pixel_format}"
+            )
+        self.dead_time = deadtime
diff --git a/src/ophyd_async/panda/__init__.py b/src/ophyd_async/panda/__init__.py
index 4007412f87..ede0115bf8 100644
--- a/src/ophyd_async/panda/__init__.py
+++ b/src/ophyd_async/panda/__init__.py
@@ -1,7 +1,6 @@
 from .panda import PandA, PcapBlock, PulseBlock, SeqBlock, SeqTable, TimeUnits
 from .panda_controller import PandaPcapController
 from .table import (
-    SeqTable,
     SeqTableRow,
     SeqTrigger,
     seq_table_from_arrays,
diff --git a/tests/epics/areadetector/test_aravis.py b/tests/epics/areadetector/test_aravis.py
index aded79ac21..3d1d8b1c42 100644
--- a/tests/epics/areadetector/test_aravis.py
+++ b/tests/epics/areadetector/test_aravis.py
@@ -77,12 +77,33 @@ async def test_deadtime_read_from_file(
     set_sim_value(adaravis.drv.model, model)
     set_sim_value(adaravis.drv.pixel_format, pixel_format)
 
-    await adaravis.drv._fetch_deadtime()
+    await adaravis.drv.fetch_deadtime()
     # deadtime invariant with exposure time
     assert adaravis.controller.get_deadtime(0) == deadtime
     assert adaravis.controller.get_deadtime(500) == deadtime
 
 
+@pytest.mark.parametrize(
+    "model,pixel_format",
+    [("UnknownCamera", None), ("Mako G-040", "UnknownFormat")],
+)
+async def test_unknown_deadtime_read_from_file(
+    model: str,
+    pixel_format: str,
+    adaravis: ADAravisDetector,
+):
+    set_sim_value(adaravis.drv.model, model)
+    set_sim_value(adaravis.drv.pixel_format, pixel_format)
+    expected_error = (
+        f"Aravis model {model} deadtimes not known"
+        if pixel_format is None
+        else f"Aravis model {model} deadtime not known for pixel_format {pixel_format}"
+    )
+
+    with pytest.raises(ValueError, match=expected_error):
+        await adaravis.drv.fetch_deadtime()
+
+
 async def test_trigger_source_set_to_gpio_line(adaravis: ADAravisDetector):
     async def trigger_and_complete():
         await adaravis.controller.arm(num=1, trigger=DetectorTrigger.edge_trigger)