diff --git a/MICADO/MASK_slit_15000x20_offset.dat b/MICADO/MASK_slit_15000x20_offset.dat
new file mode 100644
index 00000000..d1ec03b6
--- /dev/null
+++ b/MICADO/MASK_slit_15000x20_offset.dat
@@ -0,0 +1,21 @@
+# description : Slit mask for the offset long slit (15 arcsec x 20 mas)
+# author : Kieran Leschinski, Oliver Czoske
+# source : ELT-TRE-MCD-56300-0014_3.0
+# date_created  : 2026-02-03
+# date_modified : 2026-02-03
+# status : FDR design
+# type : aperture:slit_geometry
+# x_unit : arcsec
+# y_unit : arcsec
+# changes :
+# - 2019-07-10 (KL) Created the file
+# - 2020-03-24 (KL) Changed geometry to 15000x50mas
+# - 2023-07-13 (OC) Changed geometry to 15000x20mas
+# - 2023-07-24 (OC) Position in x corrected
+# - 2026-02-03 (OC) Initialised from MASK_slit_15000x20.dat
+#
+x       y
+-5.0    1.190
+10.0    1.190
+10.0    1.210
+-5.0    1.210
diff --git a/MICADO/MASK_slit_3000x16_offset.dat b/MICADO/MASK_slit_3000x16_offset.dat
new file mode 100644
index 00000000..252042d0
--- /dev/null
+++ b/MICADO/MASK_slit_3000x16_offset.dat
@@ -0,0 +1,20 @@
+# description : Slit mask for the offset short, narrow slit (3 arcsec x 16 mas)
+# author : Kieran Leschinski, Oliver Czoske
+# source : ELT-TRE-MCD-56300-0014_3.0
+# date_created  : 2026-02-03
+# date_modified : 2026-02-03
+# status : FDR design
+# type : aperture:slit_geometry
+# x_unit : arcsec
+# y_unit : arcsec
+# changes :
+# - 2019-07-10 (KL) Created the file
+# - 2020-03-24 (KL) Changed geometry to 3000x20mas
+# - 2023-07-13 (OC) Changed geometry to 3000x16mas
+# - 2026-02-03 (OC) Initialised from MASK_slit_3000x16.dat
+#
+x       y
+-1.5    1.192
+1.5     1.192
+1.5     1.208
+-1.5    1.208
diff --git a/MICADO/MASK_slit_3000x48_offset.dat b/MICADO/MASK_slit_3000x48_offset.dat
new file mode 100644
index 00000000..450b4b98
--- /dev/null
+++ b/MICADO/MASK_slit_3000x48_offset.dat
@@ -0,0 +1,20 @@
+# description : Slit mask for the offset short, wide slit  (3 arcsec x 48 mas)
+# author : Kieran Leschinski, Oliver Czoske
+# source : ELT-TRE-MCD-56300-0014_3.0
+# date_created  : 2026-02-03
+# date_modified : 2026-02-03
+# status : FDR design
+# type : aperture:slit_geometry
+# x_unit : arcsec
+# y_unit : arcsec
+# changes :
+# - 2019-07-10 (KL) Created the file
+# - 2020-03-24 (KL) Changed geometry to 3000x50mas
+# - 2023-07-13 (OC) Changed geometry to 3000x48mas
+# - 2026-02-03 (OC) Initialised from MASK_slit_3000x48.dat
+#
+x       y
+-1.5    1.176
+1.5     1.176
+1.5     1.224
+-1.5    1.224
diff --git a/MICADO/MICADO.yaml b/MICADO/MICADO.yaml
index 64e93c48..f5501492 100644
--- a/MICADO/MICADO.yaml
+++ b/MICADO/MICADO.yaml
@@ -31,6 +31,22 @@ effects:
         pixel_scale : "!INST.pixel_scale"
         filename : "INST_MICADO_wavefront_error_budget.dat"
 
+
+- name: slit_wheel
+  description: collection of field masks and slits
+  class: SlitWheel
+  kwargs:
+    slit_names:
+      - 3000x16
+      - 3000x16_offset
+      - 3000x48
+      - 3000x48_offset
+      - 15000x20
+      - 15000x20_offset
+    filename_format: MASK_slit_{}.dat
+    current_slit: "!OBS.slit"
+    include: "!OBS.slit"
+
 -   name: filter_wheel_1
     description: upper filter wheel
     class: FilterWheel
diff --git a/MICADO/MICADO_H4RG.yaml b/MICADO/MICADO_H4RG.yaml
index 0e3767ea..9e3fc291 100644
--- a/MICADO/MICADO_H4RG.yaml
+++ b/MICADO/MICADO_H4RG.yaml
@@ -52,7 +52,7 @@ effects:
     class: DarkCurrent
     # [e-/s] level of dark current for each detector
     kwargs:
-        value: 0.1
+        value: 0.01   # ELT-TRE-MCD-56300-0173_1-4
 
   - name: shot_noise
     description: apply poisson shot noise to images
@@ -67,6 +67,7 @@ effects:
   - name: border_reference_pixels
     description: Blanks the signal on N edge row and column pixels
     class: ReferencePixelBorder
+    include: False
     kwargs:
       border: [0, 0, 0, 0]
 
diff --git a/MICADO/MICADO_SPEC.yaml b/MICADO/MICADO_SPEC.yaml
index dad84b46..076bc829 100644
--- a/MICADO/MICADO_SPEC.yaml
+++ b/MICADO/MICADO_SPEC.yaml
@@ -10,17 +10,6 @@ properties :
     decouple_detector_from_sky_headers: True  # needed for slit spectroscopy
 
 effects :
--   name : spec_mode_optics
-    description : list of extra mirrors needed for the spectroscopy mode
-    class : SurfaceList
-    kwargs :
-        filename : LIST_MICADO_mirrors_spec.dat
-
-- name : spectroscopic_slit_aperture
-  class : ApertureMask
-  kwargs :
-    filename : "!OBS.slit_file"
-
 - name : grating_efficiency
   description : grating efficiency for spectral orders
   class : SpectralEfficiency
@@ -58,4 +47,4 @@ name : SPEC
 properties :
     obs_mode: "SPEC"
     fits_ins_mode: "SPE"
-    fits_ins_mask: ""
\ No newline at end of file
+    fits_ins_mask: "Small"
diff --git a/MICADO/default.yaml b/MICADO/default.yaml
index 665174d2..48923393 100644
--- a/MICADO/default.yaml
+++ b/MICADO/default.yaml
@@ -34,6 +34,7 @@ properties :
   declination : -30
   hour_angle : 0
   pupil_angle : 0
+  slit: false   # overridden in spectroscopic modes
   dit : 60
   ndit : 1
   catg : SCIENCE
@@ -115,12 +116,12 @@ mode_yamls :
   - MICADO_SPEC.yaml
   properties :
     trace_file : TRACE_MICADO.fits
-    slit_file : MASK_slit_15000x20.dat
+    slit : 15000x20
     filter_name_fw1 : Spec_HK
     filter_name_fw2 : open
     filter_name_pupil : open
     fits_ins_filt : Spec_HK
-    fits_ins_slit : "Long"
+    fits_ins_slit : Long
 
 - object : observation
   alias: OBS
@@ -131,12 +132,12 @@ mode_yamls :
   - MICADO_SPEC.yaml
   properties :
     trace_file : TRACE_MICADO.fits
-    slit_file : MASK_slit_3000x48.dat
+    slit : 3000x48
     filter_name_fw1 : Spec_HK
     filter_name_fw2 : open
     filter_name_pupil : open
     fits_ins_filt : Spec_HK
-    fits_ins_slit : "Wide"
+    fits_ins_slit : Wide
 
 - object : observation
   alias : OBS
@@ -147,12 +148,30 @@ mode_yamls :
   - MICADO_SPEC.yaml
   properties :
     trace_file : TRACE_MICADO.fits
-    slit_file : MASK_slit_3000x16.dat
+    slit: 3000x16
     filter_name_fw1 : Spec_IJ
     filter_name_fw2 : open
     filter_name_pupil : open
     fits_ins_filt : Spec_IJ
-    fits_ins_slit : "Short"
+    fits_ins_slit : Short
+
+- object: observation
+  alias: OBS
+  name: SPEC
+  description: "spectrograph: all slits"
+  status: experimental
+  yamls:
+  - MICADO_SPEC.yaml
+  properties:       # Todo: these parameters all need to be changeable
+    trace_file: TRACE_MICADO.fits
+    slit: 3000x16
+    filter_name_fw1: Spec_IJ
+    filter_name_fw2: open
+    filter_name_pupil: open
+    tech: SPEC
+    fits_ins_mode: SPE
+    fits_ins_filt: Spec_IJ
+    fits_ins_slit: Short
 
 ---
 ### default simulation parameters needed for a MICADO simulation
@@ -170,6 +189,9 @@ properties :
     wave_mid : 1.6
     wave_max : 2.5
 
+  sub_pixel:
+    flag: True
+
   computing :
     preload_field_of_views : True