diff --git a/prose/blocks/detection.py b/prose/blocks/detection.py
index 6e3b2255..00cd6fd4 100644
--- a/prose/blocks/detection.py
+++ b/prose/blocks/detection.py
@@ -19,7 +19,7 @@ def __init__(
         sort: bool = True,
         min_separation: float = None,
         min_area: float = 0,
-        minor_length: float = 0,
+        eccentricity_bound: float = 0,
         name: str = None,
     ):
         """Base class for sources detection.
@@ -38,8 +38,8 @@ def __init__(
             minimum separation in pixels from one source to the other. Between two sources, greater ADU is kept, by default None
         min_area : float, optional
             minimum area in pixels of the sources to detect, by default 0
-        minor_length : float, optional
-            minimum length of semi-major axis of sources to detect, by default 0
+        eccentricity_bound : int, optional
+            maximum eccentricity of sources to detect, by default 1
         name : str, optional
             name of the block, by default None
         """
@@ -49,7 +49,7 @@ def __init__(
         self.min_separation = min_separation
         self.threshold = threshold
         self.min_area = min_area
-        self.minor_length = minor_length
+        self.eccentricity_bound = eccentricity_bound
 
     def clean(self, sources):
         peaks = np.array([s.peak for s in sources])
@@ -68,7 +68,7 @@ def clean(self, sources):
                 for i, s in enumerate(final_sources):
                     if final_sources[i].keep:
                         distances = np.linalg.norm(
-                            s.coords - final_sources.coords, axis=1
+                            s.coords - [final_source.coords for final_source in final_sources], axis=1
                         )
                         distances[i] == np.nan
                         idxs = np.flatnonzero(distances < self.min_separation)
@@ -114,7 +114,7 @@ def regions(self, image: Image, threshold=None):
         regions = [
             r
             for r in regions
-            if r.area >= self.min_area and r.axis_major_length >= self.minor_length
+            if r.area >= self.min_area and r.eccentricity <= self.eccentricity_bound
         ]
 
         return regions
@@ -133,7 +133,7 @@ def __init__(
         min_separation=None,
         name=None,
         min_area=0,
-        minor_length=0,
+        eccentricity_bound=1,
     ):
         """Detect all sources.
 
@@ -153,8 +153,8 @@ def __init__(
             minimum separation in pixels from one source to the other. Between two sources, greater ADU is kept, by default None
         min_area : str, optional
             minimum area in pixels of the sources to detect, by default 0
-        minor_length : str, optional
-            minimum length of semi-major axis of sources to detect, by default 0
+        eccentricity_bound : int, optional
+            maximum eccentricity of sources to detect, by default 1
         name : str, optional
             name of the block, by default None
         """
@@ -165,7 +165,7 @@ def __init__(
             min_separation=min_separation,
             name=name,
             min_area=min_area,
-            minor_length=minor_length,
+            eccentricity_bound=eccentricity_bound,
         )
 
     def run(self, image):
@@ -175,7 +175,7 @@ def run(self, image):
 
 
 class PointSourceDetection(_SourceDetection):
-    def __init__(self, unit_euler=False, min_area=3, minor_length=2, **kwargs):
+    def __init__(self, unit_euler=False, min_area=3, eccentricity_bound=2, **kwargs):
         """Detect point sources (as :py:class:`~prose.core.source.PointSource`).
 
         |read| :code:`Image.data`
@@ -188,8 +188,8 @@ def __init__(self, unit_euler=False, min_area=3, minor_length=2, **kwargs):
             whether to consider sources with euler number == 1, by default False
         min_area : str, optional
             minimum area in pixels of the sources to detect, by default 0
-        minor_length : str, optional
-            minimum length of semi-major axis of sources to detect, by default 0
+        eccentricity_bound : int, optional
+            maximum eccentricity of sources to detect, by default 1
         threshold : float, optional
             detection threshold for sources, by default 4
         n : int, optional
@@ -202,10 +202,10 @@ def __init__(self, unit_euler=False, min_area=3, minor_length=2, **kwargs):
             name of the block, by default None
         """
 
-        super().__init__(min_area=min_area, minor_length=minor_length, **kwargs)
+        super().__init__(min_area=min_area, eccentricity_bound=eccentricity_bound, **kwargs)
         self.unit_euler = unit_euler
         self.min_area = min_area
-        self.minor_length = minor_length
+        self.eccentricity_bound = eccentricity_bound
 
     def run(self, image):
         regions = self.regions(image)
@@ -220,13 +220,13 @@ def run(self, image):
 
 
 class TraceDetection(_SourceDetection):
-    def __init__(self, minor_length=5, **kwargs):
+    def __init__(self, eccentricity_bound=5, **kwargs):
         """Detect trace sources  (as :py:class:`~prose.core.source.TraceSource`)
 
         Parameters
         ----------
-        minor_length : str, optional
-            minimum length of semi-major axis of sources to detect, by default 0
+        eccentricity_bound : int, optional
+            maximum eccentricity of sources to detect, by default 1
         min_area : str, optional
             minimum area in pixels of the sources to detect, by default 0
         threshold : float, optional
@@ -240,7 +240,7 @@ def __init__(self, minor_length=5, **kwargs):
         name : str, optional
             name of the block, by default None
         """
-        super().__init__(minor_length=minor_length, **kwargs)
+        super().__init__(eccentricity_bound=eccentricity_bound, **kwargs)
 
     def run(self, image):
         regions = self.regions(image)
@@ -251,7 +251,7 @@ def run(self, image):
 # backward compatibility
 class SegmentedPeaks(PointSourceDetection):
     def __init__(
-        self, unit_euler=False, min_area=3, minor_length=2, n_stars=None, **kwargs
+        self, unit_euler=False, min_area=3, eccentricity_bound=2, n_stars=None, **kwargs
     ):
         """Detect point sources (backward compatibility)
 
@@ -259,11 +259,11 @@ def __init__(
         """
 
         super().__init__(
-            n=n_stars, min_area=min_area, minor_length=minor_length, **kwargs
+            n=n_stars, min_area=min_area, eccentricity_bound=eccentricity_bound, **kwargs
         )
         self.unit_euler = unit_euler
         self.min_area = min_area
-        self.minor_length = minor_length
+        self.eccentricity_bound = eccentricity_bound
 
 
 # TODO: document
@@ -336,7 +336,7 @@ def __init__(
     def detect(self, image):
         _, median, std = sigma_clipped_stats(image.data, sigma=self.sigma_clip)
         finder = DAOStarFinder(fwhm=self.fwhm, threshold=self.lower_snr * std)
-        sources = finder(image.data - median)
+        sources = finder(image.data - median, mask=image.mask)
 
         coordinates = np.transpose(
             np.array([sources["xcentroid"].data, sources["ycentroid"].data])
diff --git a/prose/blocks/geometry.py b/prose/blocks/geometry.py
index 5ca44956..d87e9a4b 100644
--- a/prose/blocks/geometry.py
+++ b/prose/blocks/geometry.py
@@ -258,7 +258,7 @@ def __init__(self, reference_image: Image, n=10, discard=True, **kwargs):
         self._parallel_friendly = True
 
     def run(self, image):
-        if len(image.sources.coords) >= 5:
+        if len(image.sources.coords) >= 3: # changed from 5 to 3, as some SPIRIT images have very few sources
             if len(image.sources.coords) <= 2:
                 shift = self.ref_coords[0] - image.sources.coords[0]
             else:
diff --git a/prose/blocks/photometry.py b/prose/blocks/photometry.py
index eb1079ba..0418cb66 100644
--- a/prose/blocks/photometry.py
+++ b/prose/blocks/photometry.py
@@ -40,7 +40,7 @@ def run(self, image: Image):
 
         apertures = [image.sources.apertures(r) for r in radii]
         aperture_fluxes = np.array(
-            [aperture_photometry(image.data, a)["aperture_sum"].data for a in apertures]
+            [aperture_photometry(image.data, a, mask=image.mask)["aperture_sum"].data for a in apertures]
         ).T
 
         image.aperture = {"fluxes": aperture_fluxes, "radii": radii}
diff --git a/prose/blocks/utils.py b/prose/blocks/utils.py
index 137ee2ed..966423cb 100644
--- a/prose/blocks/utils.py
+++ b/prose/blocks/utils.py
@@ -622,6 +622,8 @@ def __init__(self, n=5, name=None):
 
     def run(self, image: Image):
         sigma = image.fwhm
+        self.metadata = image.metadata
+        self.header = image.header
         if len(self._images) < self.n:
             self._images.append(image)
             self._sigmas.append(sigma)
@@ -633,3 +635,5 @@ def run(self, image: Image):
 
     def terminate(self):
         self.stack = Image(easy_median([im.data for im in self._images]))
+        self.stack.metadata = self.metadata
+        self.stack.header = self.header
diff --git a/prose/core/image.py b/prose/core/image.py
index 4d0e07a8..e9191fcd 100644
--- a/prose/core/image.py
+++ b/prose/core/image.py
@@ -57,6 +57,9 @@ class Image:
 
     header: Optional[Header] = None
     """FITS header associated with the image (optional)"""
+    
+    mask: Optional[np.ndarray] = None
+    """Mask (commonly used for bad pixels) that is written in the CleanBadPixels block"""
 
     _wcs = None
 
diff --git a/prose/fluxes.py b/prose/fluxes.py
index 71827614..6bc2e373 100644
--- a/prose/fluxes.py
+++ b/prose/fluxes.py
@@ -113,7 +113,7 @@ def auto_diff_1d(fluxes, i=None):
 
         def best_weights(j):
             _w = w.copy()
-            _w[idxs[j::]] = 0.0
+            _w[idxs[j:]] = 0.0
             _w[i] = 0.0
             return _w
 
@@ -296,7 +296,7 @@ def diff(self, comps: np.ndarray = None):
         differential :code:`Fluxes`
         """
         if comps is not None:
-            weights = np.zeros(self.fluxes[0:2])
+            weights = np.zeros((self.fluxes.shape[0], self.fluxes.shape[1]))
             weights[:, comps] = 1
         else:
             weights = None