I examined the use of a single lens system for the available range of focal lengths, for the required magnification and found that a focal length of at most 100 mm would be required to sufficiently cover the object distance range. This would greatly compromise with the f-number and hence lead to a lot more spherical aberrations.

Therefore, a two lens system would be more useful to implement. Using an eyepiece of 1” puts an additional constraint on the system such that the separation between the lenses must now at least equal or be greater than half the image distance from the first lens to ensure that no light from the light cone is lost. This is clarified in the schematic. The image from the first lens in absence of the second lens would form at point A, subtending an angle θ. In order to ensure that no part this light cone emerging from the first lens is lost, the second lens must be placed at a distance atleast v/2 from the first lens.

A combination of 125mm focal length 2” diameter objective with a 250 mm 1” eyepiece covers the required range of object distances (650mm to 1500 mm). Increasing the focal length of the eye piece increases the minimum object distance accessible to 700 mm. 

A glance at the accessible u, v points shows that all magnifications are not possible at a given object distance. To image the entire surface of the test mass, a distance of at least 1.25m is required from the objective, while a beam spot of 1'' diameter can be imaged easily at upto 1200 mm from the objective . This holds true even for the 150-250 mm biconvex 2" lens combination proposed earlier. 

If this sounds reasonable, we could proceed with ordering the lenses.

[Paco, Anchal]

- Started zoom stream; thanks to whoever installed it!
- Spent some time trying to understand how anything we did last thursday lead to the sensing matrix change, but still cannot figure it out. 
- Tracking back on our actions, at ~10:30 we ran burt Restore with the 08:19/.*snap and in lack of a better suspect, we blame it on that action for now.

# ARM locking??
- Reading (not running) the scripts/XARM/lockXarm.py script and try to understand the workflow. It is pretty confusing that the result was to lock Yarm last time.
- It looks like this script was a copy of lockYarm.py, and was never updated (there's a chance we ran it for the first time last thursday)
- *Is there a script to lock the Arms?* Or should we write one? To write one, we first attempt a manual procedure;
    1. No need to change RFPD InMTRX
    2. All filters inputs / outputs are enabled 
    3. Outputs from XARM and YARM in the Output matrix are already going to ETMX and ETMY
      - Maybe we can have the ARM lock engage by changing the MC directly?
    4. Change C1:SUS-MC2_POS_OFFSET from -38 to -0, and enable C1:SUS-MC2_POS_OFFSET_ON
    5. Manually scan MC2_POS_OFFSET to 250 (nothing happens), then -250, then back to -38 (WFS1 PIT and YAW changed a little, but then returned to their nominal values)
      - Or maybe we need to provide the right gain...
    6. Disabled C1:SUS-MC2_POS_OFFSET_ON (back to nominal state)
    7. Look into manually changing C1:LSC-XARM_GAIN;
      From the command line using python:
      >> import epics
      >> ch_name = 'C1:LSC-XARM_GAIN'
      >> epics.caput(ch_name, 0.155) # nominal = 0.150
      - Could be unrelated, but we noted a slow spike on C1:PSL-FSS_PCDRIVE (definitely from before we changed anything)
      - Still nothing is happening
    8. Changed the gain to 0.175, then back to 0.150, no effect... then 0.2, 0.3 ...
      - Stop and check SUS_Watchdogs (should not have changed?) and everything remains nominal
      - Revert all changes symmetrically.
      - Could we have missed enabling FM1?
      - Briefly lost MC lock, but it came back on its own (probably unrelated)

- Wrap it up for the day. In summary; no harm done to our knowledge.

For the arm locking, the "Restore Xarm (XARM POX)" script from the "IFO_CONFIGURE" MEDM screen should get you there (I just checked it and it works fine). It is worth getting a hang of the PDH signal chain (read what the script is doing and map it to the signal chain) so you get a feel for where there may be offsets, saturations, what the trigger logic is etc. The LSC overview screen is supposed to be pretty intuitive (if you think it can be improved, I'd love to hear it but please don't change it without documenting) and there are also the webviews of the simulink models (these are RO so feel free to click around, for the LSC the c1lsc model is the relevant one).

[Paco, Anchal]

- Today we spent the morning shift debugging SUS input matrix diagonalization. MC stayed locked for most of the 4 hours we were here, and we didn't really touch any controls.

[Paco, Anchal]

• Found IMC locked upon arrival.
• Since "allegra" was set up as an additional workstation, we tried using it but discovered the monitor ist kaput. For the sake of debugging, we tested VGA and DVI inputs and even the monitor lying around (also labeled "allegra") with no luck. So <ssh> it is for now.

IMC Input sensing matrix

• Rana joined us and asked us to use Rossa for now so that we can sit socially distantly.
• Attaching some intermediate results on our analysis as pdf and zip file containing all the codes we used.
• We used channels C1:SUS-MC1_USSEN_OUTPUT  (16 Hz channels) and so on which might not be the correct way to do it as Rana pointed out today, we should have used channels like C1:SUS-MC1_SENSOR_UL etc.
• During the input matrix calculation, we used the method of TF estimate (as mentioned in 4886) to calculate the sensor matrix and inverted it and normalized all rows with the maximum absolute value element (we tried few other ways of normalization with no better results either).
• We found the peak frequencies by fitting lorentzian to the sensor data rotated by the current input matrix in the system. We also tried doing this directly on the sensor data (UL for POS, UR for PIT, LR for YAW and SD for SIDE as this seemed to be the case in the old matlab codes) but with no different results.
• The fitted peak frequencies, Q and amplitude values are in fittedPeakFreqs.yml in the attached zip.