Couple small fixes to LRS support

webbpsf/match_data.py

@@ -74,8 +74,9 @@ def setup_sim_to_match_file(filename_or_HDUList, verbose=True, plot=False, choic
             inst.image_mask = 'LYOT2300'
         elif header['FILTER'] == 'P750L':
             inst.pupil_mask = 'P750L'
-            if header['APERNAME'] == 'MIRIM_SLIT':
-                inst.image_mask = 'LRS slit'
+
+        if header['APERNAME'] == 'MIRIM_SLIT':
+            inst.image_mask = 'LRS slit'
 
     # TODO add other per-instrument keyword checks
 

webbpsf/tests/test_miri.py

@@ -196,6 +196,21 @@ def test_mode_switch():
     assert miri.aperturename == 'MIRIFU_CHANNEL2A'
     assert imager_pixelscale < miri.pixelscale < 2*imager_pixelscale
 
+
+    # Test also we can switch to LRS, and then back to a regular imaging aperture
+    # this tests another edge case for aperture and pixel scale switches
+    miri.set_position_from_aperture_name('MIRIM_SLIT')
+    assert 'IFU' not in miri.aperturename
+    assert miri.detector =='MIRIM'
+    assert miri.aperturename == 'MIRIM_SLIT'
+    assert miri.pixelscale == imager_pixelscale
+    miri.set_position_from_aperture_name('MIRIM_FULL')
+    assert 'IFU' not in miri.aperturename
+    assert miri.detector =='MIRIM'
+    assert miri.aperturename == 'MIRIM_FULL'
+    assert miri.pixelscale == imager_pixelscale
+
+
 def test_IFU_wavelengths():
     """ Test computing the wqvelength sampling for a sim IFU cube """
     miri = webbpsf_core.MIRI()

webbpsf/webbpsf_core.py

@@ -1004,6 +1004,7 @@ def aperturename(self, value):
                 # The point is to check if the pixel scale is set to a custom or default value,
                 # and if it's custom then don't override that.
                 # Note, check self._aperturename first to account for the edge case when this is called from __init__ before _aperturename is set
+                # and also check first that it's not a SLIT type aperture, for which the usual _get_pixelscale_from_apername won't work.
                 # and also check neither current nor requested aperture are of type SLIT since that doesn't have a pixelscale to get.
                 has_custom_pixelscale = (
                     self._aperturename