Updated 9/23/13 to include Ted Dunham's email with relevant TAAS information.
This is supposed to be a summary of the TAAS information from CD14. Data for Pupil Imaging and SCHP are from 2013jan9.
PUPIL IMAGING
For imaging the pupil, we compared the ZnSe and the KRS5 lenses, which are at different distances from the detector. The pupil had a set of wires taped across it as a target (
see post). The figure below shows the ZnSe and the KRS5 images. The different lenses (distances) clearly have different platescales. The location of the two images probably depends on the rotation. The focus appears better to me with the ZnSe, but hard to be quantitative. Since the detector is tilted and the focus will depend on the echelle mirror that we subsequently moved far away (these are near best echelle focus or ~5 turns), I'm not going to care too much.
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| zoom on Pupil images with ZnSe lens and KRS5 lens. The lenses were at different distances from the (tilted) detector. The SCHP was not on. |
The wires outlined in red are separated by 10.4 mm. From the intersections in pixels, I calculate pupil platescales of 0.258 mm/pixel for ZnSe and 0.207 mm/pix for KRS5, for what it is worth.
Next cooldown, we probably want to see how moving echelle mirror effect pupil focus.
SCHP
Our first image of SCHP was with it located at (144,144) in its coordinates. According to Ted Dunham's email (Feb 7, 2013), they found the DAOF TAAS matched SOFIA when it had the SCHP at (140.5,115.3), although there is no guarantee the two TAAS's are exactly alike. Our center ended up being at (131, 116). This should move us, in EXES pixels, around (-7,7). We will be moving away from the red wire outlines in the figure above.
We moved the SCHP around (with KRS5 lens in place) and found that the SCHP coordinate distances are roughly 95% the size of our pixel distances and tilted at a 45 degree angle. Moving SCHP by (0,10) gave pixel difference of (7,7), but I expect there are 1 pixel inaccuracies.
We used the SCHP images to find the location of our center and to size the cold stop relative to the secondary. According to Curtis's measurements and Bob Thompson's email, the SCHP has a 2.5 inch aperture located 2950 mm away. The LCHP has a 6 inch aperture and matches the angular size of the SOFIA secondary, so 2.5/6 = 0.42 or the SCHP is 42% the size of the SOFIA secondary. The SCHP in the ZnSe image (below) has a radius of 30 pixels and the cold stop radius is 76 pixels. These values suggest the EXES cold stop is 94% of the image of the SOFIA secondary.
Note that when we compared EXES bolted to SI flange with cart snug underneath and EXES unbolted and resting on cart (images 24 and 25, respectively), we saw a change in the location of the SCHP (but not cold stop) of ~2 EXES pixels. Based on by eye circles, looked mostly vertical in image, but difference image made it look more along the green wire.
FCLS (data from 6 Feb 13)
Finally, we tried using the FCLS. In imaging, the shape of the field suggests the F/D/S wheels were not all open/open/open. We moved the slit in place and must have noted a pixel near the center since the slit circle in image below is centered differently than imaging circles.
The plate scale based on the numbers in the figure below is roughly 21.5 EXES pixels per FCLS position unit. The same sort of 45 degree tilt is present.
Ted Dunham (Feb 7, 2013 email) has notes that say the FCLS(x,z) = (46.1, 31.9) when centered on the flange. The units for FCLS movement are millimeters and he found that 1mm FCLS motion moved the source by 4.16" on his array, which is the predicted platescale at the SOFIA focal plane to 1%.
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| Some prettied up images of the FCLS. |
For focus, we found a best focus of 6832 on the FCLS. Not sure of these units. Pretty certain that more positive means the telescope focus moves further forward (in aircraft coordinates). Ted said that their best focus was at 7050 and that +-75 counts would not be surprising. They're focus is 319 mm forward (in aircraft coordinates) of the SI mounting surface. I believe the focal range for SOFIA is -300 mm to +900 mm relative to the SI flange. Our design telescope focus should be, I believe, at +300mm or just slightly aft of Ted's.
