Hi-med spatial plate scale with FCLS: Part 2

Here is more data taken to measure the plate scale in different modes taken on the last day of CD26.
This time we used 3 widely spaced FCLS positions to obtain better leverage on the plate scale.

The three FCLS positions that were used with slit 6 (slitwidth = 3.23").
(X1,Z1)= 19.6 mm, 16.7 mm
(X2,Z2)= 25.6 mm, 21.35 mm
(X3,Z3)= 31.6 mm, 26.05 mm

separations:
P1-P2: 7.59 mm   --> 31.4"
P1-P3: 15.21 mm --> 63.0"
P2:P3: 7.62 mm --> 31.5"

Here are the three superimposed FCLS positions in the different modes (true camera, echelon camera, medium res and low res).

True camera mode: slit6, N04679

Echelon Camera mode: slit6, N04679

Medium, 2142cm-1, 12th order (57.91 deg)

Low, 2142, 6th order (24.097 deg)

Each mode was rotated (rot.pro) and extracted to a 1-D profile to fit the beam positions with Gaussian functions (clickfit.pro).

The separation between FCLS points was:
Interval                               LOW         MEDIUM   HIGHCAM  TRUECAM (EXES pixels)
P1-P2 (7.59 mm):              160.586     158.717      158.832      161.491
P1-P3 (15.21 mm):            320.243     320.330      318.124      321.236
P2-P3 (7.62 mm):              159.657     161.613      159.292      159.745

If we use the 4.14"/mm value from Ted Dunham, the plate scales are as follows

LOW          MEDIUM    HIGHCAM TRUECAM (in "/pix)

0.195534     0.197836     0.197693     0.194438

0.196726     0.196672     0.198036     0.196118

0.197298     0.194910     0.197750     0.197189

If we scale it up so that medium comes out as 0.201"/pix, as measured in lineops 2014, then the TAAS plate scales become:

LOW          MEDIUM    HIGHCAM TRUECAM (" /pix)

0.200031     0.202387     0.202240     0.198910

0.201250     0.201196     0.202591     0.200628

0.201836     0.199393     0.202298     0.201725

Platescale versus Input Angle for high-medium mode. Dashed line is with Gamma angle =5.43 deg, as per MJR's comment to this post.  

Black vs Room at 586 cm-1

Curtis took some ND pairs of Black and Room while we were on the TAAS during CD26.  I wanted to see if the KRS5 lens in front of the blackbody could be causing any of our fringing.

The data are

;;;     cold.lab.00178.fits  mirror
;;;     cold.lab.00179.fits  room temp blackbody
;;;     cold.lab.00180.fits  sky

"sky" is actually looking at the capped FCLS.  Blackbody and FCLS power had both been off a few hours before taking data, so the sources should be at room temperature.

There were 2 ND pairs in each file.  The pattern was N0 D0 T0, so there was a throwaway after each D. 

For sky and BB, the 2nd ND pair was 0.2% lower counts than the first one.  Almost like reduced response once we got going.  It would be interesting to play with this and see if more Ts helps and/or if the response drops any more with further ND pairs in the file.  

The division of room/BB is not perfect.  Room is 1.5% larger than BB. At 586 cm-1, this would be the difference between 294.5 K and 293 K.  However, there also seems to be some structure to the extra light; it isn't evenly at all pixels.  

BB divided by Room at 586 cm-1.  Image was median filtered by 5 pixels.  Atmospheric line is around (800,600).  This region is closer to 1.000 given the stretch.

Not sure what is causing extra light.  Scattering in room that isn't in BB?  If so, the scattering isn't even.  

As a side note, I looked at the S/N as a function of signal in the three sets.  To get the noise, I differenced the ND pairs in each file (and corrected for the root(2) increase in noise).  I calculated the Standard deviation of difference values for all pixels at a given number of counts.  Room and BB are basically on top of each other.  Mirror seems to have a linearly increase S/N indicating the noise is fixed (not photon?).  Would like to investigate this more since I'd have thought we'd be out of read noise by this count level (60 counts).  Also, the S/N behavior at higher count levels in Room and BB seems to plateau at too low a level.  We shouldn't be going non-linear at 1800 counts or so.  To explore further, we would need a much longer time series so the S/N could be determined at each pixel, rather than with this standard deviation of all differences at a given signal level.

S/N vs Counts for mirror (black), BB (green), and Room (red).  

Hi-med spatial plate scale with FCLS

I used the FCLS to compare the spatial plate scale in medium and hi-med modes.
I set up in HI-MED 2142cm-1, order 13  -- this mode has the longest possible slit that I could find that could operate on FCLS/TAAS temperatures. (around echelle angle 70)

I found 2 XZ coordinates with the FCLS that fit within the hi-med slit.
(X,Z)=23.92, 19.64 mm
(X,Z)=23.27,19.39 mm

I made a "nod-off" frame by sending the FCLS "home" X,Z=0,0.

Then I made artificial "NOD_OFF_SLIT" files, ran through through the pipeline, and let the pipeline find the beams at the MAKE PROFILES/ FIND OBJECTS stage.
I took the median value for these beam positions over the 14 orders--
and this worked out to
25.8 pixels /mm for HI-MED

I did nearly the same procedure to measure the slit motion in medium mode for a known X,Z fcls motion.

19.6 pixels / mm for MEDIUM



Other notes:
FCLS robofocus is a lost-- with quick camera mode focus run I found the best value to be 10250 steps, (compared to 6800 steps when it was calibrated properly).

FCLS aperture control is stuck near the 1mm aperture. It is in a usable position, but not quite truly aligned, based on difference in where it hits the EXES window when the FCLS XZ stage is placed at the "boresite" and the window center positions. R. Porter has been alerted.

To convert X,Z fcls coordinates to EXES x,y detector coordinates --
(x', y' are X,Z on the FCLS controls).

Δx' = Δx cos (44.4) - Δy sin (44.4)

Δy' = -Δx sin (44.4) - Δy cos (44.4)