Here's our first try, scanning the fattest (flux) slit across the IR spot at our knife-edge-test-indicated best focus:
Photometry-box plots of image strength as a function
of slit position, taken near knife-edge best focus.
The three curves are generated in the FORCAST gui for boxes placed at various points on the image. This is a strip-chart plot of the signal as the slit is slowly scanned across the spot, the timing is such that each data point in the plot corresponds to abut two steps of the slitwheel motor. I think two steps is worth roughly 10 µm of slit movement, and by eyeball I count about eight data points for a 20%/80% 'risetime' in the plot. If this is right, we cut off the spot in about 80µm of slit travel. The red line is from a small box placed on one of the narrow mode lines created by the neutral-density filter....we can ignore the green and blue curves.
For comparison, here is the equivalent slit-scan for the nominal best focus position...it's pretty clear this is not the right place.
Photometry-box plots of image strength as a function
of slit position, taken the nominal focus position.
Finally, here is an equivalent plot using the twin 'V-Slit' feature, showing that the spot is small enough to be almost completely blocked by the narrow separator between the V-Slits:
Photometry-box plots of image strength as a function
of slit position, taken near knife-edge best focus.
1 comment:
The V-slits are supposed to be 151 microns across, according to the dxf file that was used. At the center of the slit aperture (ie, the same radius of the slit wheel as the pinhole), the v-slits are supposed to be 485 microns apart (edge-to-edge, not center to center).
Looking at the trace for the v-slit, it seems both slits are 19 steps wide FWZI. If each one is 10 microns of slit movement, and we don't forget about the spot size (which should be about 90 microns diameter for the 0.0125" BB aperture), our slits are either narrower or the spot is; you'd expect FWZI to be more like 24 steps. If the BB aperture was the 25 micron pinhole, then the spot should be diffraction limited or about 50 microns at the slit and the FWZI should be something like 20 steps. Did you use the 25 micron aperture on the BB?
The high spot between the slits is about 16 steps. You'd expect the high spot to be 485 - 2 * 90 = 300 microns or 30 steps. Here, either the slits are closer together than on the dxf or the spots are much bigger (not smaller, like above).
Overall, it looks pretty good. You could put in the pinhole and see how many pixels it moves with a slit motor move of about 50 step to try and calibrate motions.
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