While attempting to develop a somewhat accurate noise budget for the 40m, I reasoned that while the shape of the transfer function for the ISS is important, the degree to which we can 'tune' it to a particular experiment/application is limited.

• Since we're using a DC-coupled servo, the TF magnitude will go like f^k with k < 0 for low frequency.
• The UGF will be somewhere around 10 kHz to 1 MHz (most likely right around 100 kHz) as beyond 1 MHz, the gain of our servo is limited by the GBWP of the op-amps.
• We need around 3 or 4 orders of magnitude of gain in the 1-100 Hz range based on this, with gain > 10 for f < 10 kHz

Beyond that, we're sort of limited by the desired high and low frequency behavior as well as the general principle that more electronics = more noise so we probably don't want more than 3 or 4 filter stages, if that. Additionally, the ISS can be over-engineered so that it suppresses the laser noise to levels well below other fundamental noise sources over the important regime ~10 - 10^3 Hz without particular regard to a noise budget.

The design I propose is very similar to a previous design, with a few adjustments. It consists of 3 filter stages that easily be modified to increase gain for higher frequencies if it is known/determined that the laser being stabilized has a lot of high frequency noise.

Stage 1: Basic LP Filter + Establish UGF (each stage 'turning on' will not change the UGF),  Stage 2: Integrator with zero @ 10 kHz,  Stage 3: Optional extra gain if necessary

With the full TF given by,

As usual we consider the noise caused by the servo itself. Noise analysis in LISO is done with a 1 V input excitation.

This servo should function sufficiently for the 40m.

Tonight I looked at the signal from a geophone and accelerometer side by side, in order to see if they show the same ground motion and if the sensitivity factor I am using to convert from V to m/s is right. This is plotted below, along with the current estimates for accelerometer and geophone noise:

From this it is pretty clear that at least one of the sensitivity factors (V/m/s) I am using is wrong (the noise levels are much lower than the ground motion, so they can't account for the difference). I suspect it is the geophone one, because Wilcoxon provided these sensitivities for each individual accelerometer, but I was just using the number I found in online specs for the geophones.

The reason the online value is wrong is probably because of the value of the shunt resistor, a resistor that just goes across the top of the geophone (its purpose is to provide damping, by Lenz's Law). The specs assume a value of 380 Ohm, but I measured the one in the STACIS to be about 1.85 kOhm.

Assuming the accelerometer signal is correct, I multiplied the geophone signal by different factors to try to get an idea of what the true calibration factor is, and found that a value of 0.25 (m/s)/V gives decent agreement at higher frequencies (below 10 Hz the sensitivity drops off, according to the online specs). This is shown below:

Above, the geophone noise was recalculated with the new sensitivity and assuming that both geophones in the noise measurement had the same sensitivity. I took the transfer function of two geophones side by side to see if their gains were dramatically different; this plot is shown below. The coherence is only good for a small band, but looking at that band the gain is approximately unity, implying very roughly that the sensitivity of each is approximately the same. The lack of coherence is strange, and I'm not sure what the cause is. Even using the shaker near the geophones only improved the coherence slightly.

This week I've looked into finding an accurate sensitivity for the geophones in the STACIS. I found that when placing a geophone and accelerometer side by side, and using the sensitivity values I had from spec sheets, the readings were very different (see eLog 7054: http://nodus.ligo.caltech.edu:8080/40m/7054).

I cut the shunt resistor off one of the STACIS geos and found it to be 4000 Ohm, which is one of the standard values for this geophone model. When it is connected to the geophone the net resistance is 2000 Ohm (I took a more careful measurement, I took the geophone out). Then the internal coil resistance should be 4000 Ohm, if they are connected in parallel. However, the geophone spec sheet does not have a sensitivity value for this exact scenario, so I'll have to find a different way to determine the calibration (maybe by putting it next to a seismometer with a known sensitivity). So I know for sure that the sensitivity value I was originally using is wrong, because it assumed an internal coil resistance of 380 Ohm, but I have to check if the value I found by forcing the geophones to agree with the accelerometers (eLog 7054 --> 0.25 (m/s)/V) is correct.

I've also been looking again at the open loop gains of the STACIS (see eLog 7058: http://nodus.ligo.caltech.edu:8080/40m/7058). Attached is what TMC, which makes the STACIS, says it should look like (with a 4000 lb load on the STACIS). Today I am taking the open loop gains into higher frequencies to get a better comparison, but the plots look quite similar to what I have so far. So if it is an unstable open loop gain, then it's at least not new.

The attached file is a python notebook that you can use to get data. Minimal syntax.

Minute trend data seems not available using the NDS2 server. Its super slow using dataviewer from the control room.

Did some digging into the NDS2 config on megatron. It hasn't been updated in 2 years.

All of the stuff is run by the user 'nds2mgr'. The CronTab for this user was running all the channel name updates and server restarts at 3 AM each day; I've moved it to 5:05 AM. I don't know the password for this user, so I just did 'sudo su nds2mgr' to become him.

On megatron, in /home/nds2mgr/nds2-megatron/ there is a list of channels and configs. The file for the minute trend (C-M-ChanList.txt), hasn't been updated since Nov-2015. ???

We tried to acquire data from the seismometers and the mode cleaner using the Matlab function

datalist = NDS2_GetData({'C1:PEM-SEIS_GUR1_X_IN1_DQ'}, 996258376 , 10, CONFIG.nds.C)

and encountered the following error

Warning: daq_request_data failed
 
??? Error using ==> NDS2_GetData
Fatal Error getting channel data.

The same error was obtained with the following other channels

C1:PEM-SEIS_GUR2_X_IN1_DQ

C1:PEM-SEIS_STS_1_X_IN1_DQ

But we are able to get data from channel

C1:LSC-MC_OUT_DQ

for the same gps time.

We checked with Dataviewer that the data are saved (we viewed data of last 24h) for every channel.

I'm working on getting the input beam centered on the Yarm optics.  To do this, I measured the spot positions, move the tip tilts, realign the cavity, then measure the new spot positions.  While doing this, I am also moving the BS and Xarm optics to keep the Xarm aligned, so that I don't have to do hard beam-finding later.

Here is the plot of spot measurements today.  The last measurement was taken with no moving, or realigning, just several hours later after speaking with our Indian visitors.  I'm closer than I was, but there is more work to do.

[Reuben, Radhika]

Checked out the AUX PDH locking system at the XARM. Started by locking the AUX laser using the uPDH servo box and adjusting the test masses to maximize transmission (~0.6 achieved). There were some issues where the fundamental mode would be briefly visible and then lose lock. Higher order modes were also seen which could be removed by adjusting test masses. We also noticed the laser spot moving around a lot, as if the test masses were swaying. Finally after repeated tries we managed to lock and hold the laser to the cavity long enough to measure the open loop transfer function using the Moku:Go frequency response analyzer tool. Got an idea of the finicky and temperamental nature of the locking process.

Taking the transfer function data from the Moku:Go and using a Python script, found the UGF to be around 25.6 kHz and phase margin to be around 25.5 deg. My current goal is to keep reading up on control systems and related theory (I still feel like I lack understanding of the important principles needed), and parallelly making a small script that can take the transfer functions data and calculate some useful information (halfway done).

One issue I found with the script was that the Python control library was giving me a wrong value of Gain Margin (~0.26 where ~-5 was expected) while using the control.margin function. The other parameters phase margin and crossover frequencies agree with the data visually.

Kiwamu and I noticed that there is a ghost beam on the green beam going into the ETM. What we see is some interference fringes on the edge of the transmission of the green beam through the dichroic beam splitter (DCBS). If we look at the reflection from the dichroic beam splitter these are much more pronounced.

The spacing of the fringes (about 2 per 10mm) indicates an angle between the fields of around 0.1 mrad.

We were able to cause significant motion of the fringes by pushing on the knobs of the steering mirrors that steer the beam into the DCBS. A rough calculation of the derivative of optical path difference between the ghost and the primary beam as a function of input angle gives about 15 microns per mrad. What filtering the effect the arm cavity will have on the ghost beam is not immediately clear, but the numbers shouldn't be too difficult to determine.

The beam splitter (BS1-1064-33-2037-45S) that is currently being used has an antireflection coating on the second surface and a wedge of less than 5 arcmin; yet it leads to ghosting as shown in the figure attached (courtesy: Thorlabs). I'm also attaching its spec sheet I dug up on internet for future reference.

I came across pellicle beamsplitters, that are primarily used to eliminate ghost images. Pellicle beamsplitters have a few microns thick nitrocellulose layer and superimpose the secondary reflection on the first one. Thus the ghost image is eliminated. 

Should we go ahead and order them? (https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=898

https://www.edmundoptics.eu/c/beamsplitters/622/#28438=28438_s%3AUGVsbGljbGU1&27614=27614_d%3A%5B46.18%20TO%2077.73%5D)

you have to use a BS with a larger wedge angle (5 arcmin ~ 1 mrad) so that the beams don't overlap on the camera

[Gautam, Kruthi]

This afternoon, Gautam helped me setup Giada to access the GigE installed for MC2. Unlike Paola, which was being used earlier, Giada has a better battery life and doesn't shutdown when the charger is unplugged. Gautam configured Giada to enable its wireless connection to Martian, just like Koji had configured Paola (https://nodus.ligo.caltech.edu:8081/40m/14672). We also rerouted  the ethernet cable we were using with the PoE adaptor from Netgear Switch in 1x2 to 1x6.

Turns out, focusing the GigE is actually a bit tricky. With pylon, everytime I change the exposure or the focus, I'm running into the error I had mentioned earlier in one of my elogs; so I tried using the python scripts to interact with the GigE. But whenever I try to change the focal plane distance by rotating the lens coupler, the ethernet cable connection becomes loose and the camera server needs to be relaunched every now and then. Also, everytime we want to change the distance between the lenses, the telescope needs to be dismantled and refocused again. I'll try to come up with a better telescope design for this.

Yesterday, I had focused the GigE using a low exposure time and small aperture of iris, to make sure that we are actually seeing a sharp image of the beam spot. I'm attaching a picture of the beam spot I had clicked while focusing it, unfortunately, I forgot to take a picture after I had focused it completely. I'm also attaching a picture of the final setup for future reference. 

Yesterday night, Rana asked me to lock the MC2. I figured that the PSL shutter was closed; I just opened it and was able to see the beam spot on the analog camera screen.

The GigE is focused now (judged by eye) and I have closed the lid. I'm attaching a picture of the MC2 beam spot, captured using GigE at an exposure time of 400µs.

What was the solution to resolving the flaky video streaming during the alignment process????

-> I think, the issue was with either the poor wireless network conection or the GigE-PoE ethernet cable.

I've started setting up the last new rackmount SuperMicro as a dedicated server for the GigE cameras. The new machine is currently sitting on the end of the electronics test bench. It is assigned the hostname c1cam at IP 192.168.113.116 on the martian network. I've installed Debian 10, which will be officially supported until July 2024.

I've added the /cvs/cds NFS mount and plan to house all the client/server code on this network disk. Any dependencies that must be built from source will be put on the network disk as well. Any dependencies that can be gotten through the package manager, however, will be installed locally but in an automated way using a reqs file.

We should ask Chub to reorder several more SuperMicro rackmount machines, SSD drives, and DRAM cards. Gautam has the list of parts from Johannes' last order.

This past week, I have building a sine wave rectifier and trying to write a simple program that displays a ccd image to familiarize myself with the code.  I also wrote a progress report in which I included the following images of the sine wave rectifier circuit as well as the optical chain including the phase-locked loop.  The hirose connector arrived so I can begin soldering the electronics together and testing the trigger box with the ccd.  I am waiting on the universal PDH box as well as another fiber coupler to begin setting up the optics.  In order to avoid the frustrations associated with sending a laser beam down a long pipe to an optical bench across the room, I will be transmitting laser 1 to the ccd by means of a fiber optic cable and dealing with the alternative new and exciting frustrations.

The plan for the optical setup has been corrected after it was realized that it would be impossible to isolate a 29.501 MHz frequency from a 29.499 MHz one because they are so close in value.  Instead, we decided to adopt the setup pictured below.  In this way, the low-pass filter should have no trouble isolating 29.501-29.5 MHz from 29.501 + 29.5 MHz.  Also, we decided to scrap the idea of sending Alberto's laser through a fiber optic cable after hearing rumors of extra lasers.  Since I shouldn't have to share a beam when the second laser comes in, I plan on setting up both lasers on the same optics bench.  I've been working on the software while waiting for supplies, but I should be able to start building the trigger box today (assuming the four-pair cable is delivered).

Today, I moved the router from on top of the PSL into the control room in order to perform dark field tests on the GC650 (which I also moved).  The GC750 along with the lens that was on it and the mount it was on has been lent to Ricardo's lab for the time being.  I successfully triggered the GC650 externally and I also characterized the average electronic noise.  For exposure times less than 1 microsecond, the average noise contribution appears to be a constant 15 on a 12-bit scale.

Lately, I have been able to externally trigger the camera using a signal generator passing through the op-amp circuit that I built.  The op-amp circuit stabilizes the jitter in the sine wave from the signal generator and rectifies the wave.  I wrote the calculations into the code allowing me to find the phase and amplitude from the images I take.  I still need to develop code that will plot these arrays of phase and amplitude.

The mysterious dark band at the top of the ccd images continues to defy explanation.  However, I have found that it only appears for short exposure times even when the lens is completly covered.  During the next couple of days, I will try to write a routine to correct for this structure in the dark field.

Koji recommended that we use the optical setup pictured below.  This configuration would require fewer optics and we would have to rely on slight misalignments between the carrier and reference beams to test the effectiveness of the phase camera instead of a wavefront-deforming lens.

This past week, I have mostly been debugging my software.  I have tried to use the fluorescent lights to test the camera, but I can't tell for sure if my code is finding the correct amplitude and phase or not.  I am currently using Mathematica to double check my calculations in solving for the phase and amplitude.

Also, I have taken dark field images using a lens with a closed shutter.  I have found that the dark band across the top of the images only appears after the camera heats up.  Also, there is an average electronic noise of 14 with a maximum of 40.  However, this electronic noise as well as any consistent ambient noise will be automatically corrected for in the calculations I'm using because I'm taking the differences between the CCD images to calculate relative phases and amplitudes.

I should be able to start setting up optics and performing better tests of my software this week.

This week, Joe and I have been setting up the laser and optics.  The mephisto laser is emitting a very ugly beam that we can hopefully remedy using an iris and a lens.  After scanning the beam width at a few different distances from the laser, I am currently trying to determine the appropriate lenses to use.

While aligning the optics, we tried to start up the CCD.  Although nothing should have changed since the last time I used it, the code claimed it could not find the camera.  All the right leds are lit up.  The only indication that something is awry is that the yellow led on the camera isn't blinking as it does when there is ethernet activity.  

The camera wasn't working because the router has no built-in dhcp server.  We had to manually start the server after rebooting the computer.

One of the additional GigE cameras has been IP configured for use and installation. 

Static IP assigned to the camera- 192.168.113.152
Subnet mask- 255.255.255.0
Gateway- 192.168.113.2
 

GigE can be connected to ethernet. AR coated 1064 f50 can arrive any day now.

The 50mm lens has arrived. (Delivered yesterday).

Also the GigE has been wired and conencted to the Martian. Image acquisition is possible with Pylon.

All thanks to Steve, we cleaned the view port on the ETMX on which the camera is installed, and with a little fine tuning of the focus of the camera, here's a really good image of the beam spot at 6 and 14 ms.

Today Steve and I tried to to capture the image of scattering of light by dust particles on the surface of ETMX using GigE camera. The image ( at gain =100, exposure time = 125000) obtained has been attached. Unlike the previous images, a creepy shape of bright spots was seen. Gautam helped us lock infrared light and see the image. A similar less intense shape was seen. This may be because of the dust on the lens.

We should move on with getting this lens from Edmonds #67-717  at 1064 R<3% 

Computar M5018-SWIR is an other choice

AR coatings 500 - 1100nm R<1% are expensive.

Not that this is an urgent concern, just a data point which shows that it doesn't just not work at the sites.

I had to restart the dhcpd server on Ottavia that allows us to talk to the camera.  I then also changed the configuration script on the camera so that it no longer thinks ottavia is 131.215.113.97, but correctly 192.168.113.97.  Overall took 5 minutes.

I also looked up services for Centos 5, and set it using the program serviceconf to start the DHCP server  when Ottavia is rebooted now.  That should head off future problems of that nature.  For reference, to start the dhcp server manually, become root and type "service dhcpd start".

Following the death of rossa, which was hosting the only working environment for the GigE camera software, I've set up a new dedicated rackmount camera server: c1cam (details here). The Python server script is now configured as a persistent systemd service, which automatically starts on boot and respawns after a crash. The server depends on a set of EPICS channels being available to control the camera settings, so c1cam is also running a softIOC service hosting these channels. At the moment only the ETMX camera is set up, but we can now easily add more cameras.

Usage

Instructions for connecting to a live video feed are posted here. Any machine on the martian network can stream the feed(s). The only requirement is that the client machine have GStreamer 0.10 installed (all the control room workstations satisfy this).

Code Locations

As much as possible, the code and dependencies are hosted on the /cvs/cds network drive instead of installed locally. The client/server code and the Pylon5, PyPylon, and PyEpics dependencies are all installed at /cvs/cds/rtcds/caltech/c1/scripts/GigE. The configuration files for the soft IOC are located at /cvs/cds/caltech/target/c1cam.

Upgrade Goals

The 40m GigE camera code is a slightly-updated version of the 10+ year-old camera code in use at the sites. Consequently every one of its dependencies is now deprecated. Ultimately, we'd like to upgrade to the following:

• Python 2.7 --> 3.7
• Basler Pylon 5.0.12 --> 5.2.0
• PyPylon 1.1.1 --> 1.4.0
• GStreamer 0.10 --> 1.2

This is a long-term project, however, as many of these APIs are very different between Python 2 and 3.

To verify the Pylon Installation on the shared drive, I tried connecting the Basler acA640-100gm to the PoE connector and running it through Allegra.

Each time the camera was opened, I got a message on Terminal saying ‘Failed to get the node ‘AcquisitionFrameRate’ from the device’s nodemap’.

Yet, I was able to capture images in single shot and continuous shot mode. I tried to emulate the analog controls (gain at 360, Black level 121) as in Johannes’ elog  12617 and varied the exposure rate from 1 to 5 milliseconds. The camera had the Rainbow 50mm lens with which I was able to focus on some markings on the white board, however the image was extremely magnified and this lens was extremely sensitive which meant that the image went quickly out of focus.
I checked the CCD cabinet in the 40m to find 12 mm lenses which couldn’t focus properly. So I couldn’t quite get an image as Johannes had been able to obtain! I also got an image of a cable in focus but it is very dark due to the exposure time.
 WIth the components for the telescope design arriving(hopefully) by tomorrow, I should be able to assemble the telescope and capture some more images.

From Joe B’s paper and discussion with Gautam and Johannes, I came up with three models for configuring the GigE’s. Three configuration models for the GigE have been proposed which connect the camera to a computer network. While the first model is just involves connecting the camera directly to a PC with Pylon installation using a Power over Ethernet adapter, it would be only efficient in the basic IP configuration of the camera without involving a complex network. The second model describes the integration of the camera to 'Martian'. The third model combines the creation of a separate camera subnetwork and integrating this network with the main network in the lab through a switch. This model would be more efficient to employ as the number of cameras increases. The same purpose could be achieved by using a PC with two network ports one of which connects to the camera subnet while another links it to the Martian where the computers running the client script could stream desired frames.

This evening I was able to obtain some images with the same lens on the GigE. 
The problem earlier, as Johannes pointed out, was that we were using too many adapters on the camera and so it was able to focus at really shallow distances or at really low depths of focus. 
So after removing the adapters we were able to focus on objects at much larger distances.

The mug for example was at a distance greater than 1.5 meters from the camera.

Here are some images that were captured on Allegra by plugging in the GigE to the PoE connector connected to the Martian. 

And here's another picture of Kaustubh, my fellow SURF, captured in all his glory by Rana! :)

50mm 1.8 lens with Basler camera at MC2 face with micro clamp 350617    Camera manuals plus

I tried to capture some images with the GigE inside the Interferometer area in the 40m today. For that, I connected the POE injector to the Netgear Switch in 1x6 and connected it to the GigE. I then tried to access the Pylon Viewer App through Paola but that seemed to have some errors. When trying to connect to the Basler, quite a few errors were encountered in establishing connection and trying to capture the image. There were a few errors with single shot capture but the continuous shot could not even be started. To locate the problem, I tried running the Pylon installation through Allegra in the control room and everything seemed to work fine there.

Few error messages encountered

createPylondevice error :Failed to read memory at 0xc0000000, 0xd800 bytes. Timeout. No message received.
Failed to stop the camera; stopgrab: Exception Occurred: Control Channel not open

Eventually I connected Paola to the Switch with an Ethernet cable and over this wired connection, the errors were resolved and I was able to capture some images in Continuous shot mode at 103.3 fps without any problem.

In the afternoon, Steve and I tried to install the camera near MC2 and get some images of the mirrors. Due to a restricted field of view of the lens on the camera, after many efforts to focus on the optic, we were able to get this image. MC2 was unlocked so this image captures some resonating higher order mode.

With MC2 locked, I will get some images of the mirror at different exposure times and try to get an HDR image.  
As per Rana's suggestion, I am also looking up which compression format would be the best to save the images in.

Thanks to Steve and Gautam, the IMC was locked.

I was able to capture images with the Rainbow 50 mm lens at exposure times of 100, 300, 1000, 3000, 10000 and 30 microseconds.(The pictures are in the same order). These pictures were taken at a gain of 300 and black level 64.

Special credits to Steve spent a lot of time help me a with setting up the hardware and focusing on the beam spot with the camera. 
I can't thank you enough Steve! :) 

Good installation. I think the images are still out of focus, so try to resolve into some small dots at the low exposure setting.

Chub and I are trying to figure out a way to co-mount GigE into the existing cylindrical enclosure. I'm attaching a picture of the current setup that is being used for imaging MC2. As of now, I have thought of 3 possible setups (schematics attached); but I don't know how feasible they are. Let us know if you have any other ideas.

Update: The setup 3 would require us to use the 52cm long enclosure. It has a long breadboard welded to it, which makes it very convienient, but the whole setup becomes quite heavy and it's not that safe to install such heavy enclosure on top of the vaccuum system. Also, aligning its components would be more complicated than other setups.

I decided to start with the simple one, therefore, I tried implementing setup 1. Fitting in the analog camera horizontally alongside the telescope turned out to be tricky. Though I did manage to fit it in, it didn't leave any room to change the orientation of the beamsplitter. Like Koji suggested, I'll be trying the setup 2.

I managed to fit all the parts into the cylindrical enclosure without having to drill a hole in the enclosure to mount the analog camera (pictures attached); thanks to Koji for helping me find some fancy mechanical components (swivel post clamps, right angle post clamps and brackets). On Thursday, with Chub's help, I took a look at all the current analog camera positions with respect to the cylindrical enclosures. I think this setup gives me enough flexibility to align the components, as necessary, to be able to image the test masses/mirrors in all the cavities. I'll set it up for MC2 tomorrow.

[Kruthi, Milind]

Today, with Milind's help, I installed the analog camera into the MC2 enclosure [picture attached]; but it is not yet focused. We replaced the bulky angular bracket with a simple one, this saved a lot of space inside and it's easier to align other components now. I'll finish setting it up tomorrow.

Telescope design for MC2:  Instead of using two 3" long stackable lens tubes (SM2L30), we can use one 3" lens tube with an adjustable lens tube (SM2V10), as shown in the picture. This gives a flexibility to change the focal plane distance by 1" and also reduces the overall length of telescope from 9 inches to 6-7 inches. I decided to use two 150mm biconvex lens instead of a combination of 150mm and 250mm lenses, as the former combination results in lower focal plane distance for a given distance between the lenses.

Specifications of current telescope system (for future reference):

With the above telescope, assuming the MC2 mirror to be at a distance of approx 75cm, the focal plane distance will range from 7.9cm to 8.1cm. Using the adjustable lens tube, we can further make the fine adjustment.

[Koji, Kruthi]

Yesterday, Koji helped me clean all the optics that are being used for the setup. We tried aligning the cameras with the previous configuration we had, but after connecting the analog camera cables there wasn't much room to align the beam splitter. Today, I tried a different configuration and tested the alignment of analog camera, GigE, beam splitter and the mirror using a laser beam [pictures attached]. But the MC2 isn't locked to test if the whole setup is actually aligned with the mirror inside the vacuum. 

Also, with this setup, just by using posts of different lengths with the middle 90º-post-clamp, we will be able to move all the components. This way, we can easily image the beam spot in all the cavities.

I'm attaching a picture of the screen. I just positioned the enclosure by turning it a bit and I suppose we can see the mirror inside the vacuum now (the MC2 is still not locked). 

don't need to lock - make sure the 4 OSEMs are centered on the camera field just as we have for the arm cavity mirrors