For some time there have been intermittent focus problems with the system – especially the VE2 filter would go in and out of focus for no discernable reason. The focus is supposedly set, in scripted mode, by referring to focus positions from a script. The currently used focus positions are:
[FOCUSPOSITIONS]
; The names made of (Color filter) + (ND filter) + (Knife Edge DF)
IRCUT_AIR_SKE = “28750”
IRCUT_ND_SKE = “29000”
B_AIR_SKE = “28250”
B_ND_SKE = “29000”
V_AIR_SKE = “30750”
V_ND_SKE = “29000”
VE1_AIR_SKE = “28750”
VE1_ND_SKE = “29000”
VE2_AIR_SKE = “24000”
VE2_ND_SKE = “29000”
AIR_AIR_SKE = “29000”
AIR_ND_SKE = “29000”
As the focus seemed more and more unreliable I defined a new set of positions in order to be able to test on stars from 28000 to 31000:
FOCUS090 = “28000”
FOCUS091 = “28100”
FOCUS092 = “28200”
FOCUS093 = “28300”
FOCUS094 = “28400”
FOCUS095 = “28500”
FOCUS096 = “28600”
FOCUS097 = “28700”
FOCUS098 = “28800”
FOCUS099 = “28900”
FOCUS100 = “29000”
FOCUS101 = “29100”
FOCUS102 = “29200”
FOCUS103 = “29300”
FOCUS104 = “29400”
FOCUS105 = “29500”
FOCUS106 = “29600”
FOCUS107 = “29700”
FOCUS108 = “29800”
FOCUS109 = “29900”
FOCUS110 = “30000”
FOCUS111 = “30100”
FOCUS112 = “30200”
FOCUS113 = “30300”
FOCUS114 = “30400”
FOCUS115 = “30500”
FOCUS116 = “30600”
FOCUS117 = “30700”
FOCUS118 = “30800”
FOCUS119 = “30900”
FOCUS120 = “31000”
I then ran, in steps of 100, over all these positions in all filters for 5-15 images in each position. I fitted a Moffat profile to the brightest source in each image and plot here the radius (sqrt(rx² + ry²)) of the profile:
[Sorry for the poor quality of that plot – a downloadable pdf of that plot is here:
The width of the distribution of points is due to repeated trials in some cases. Scattered points far from the general relationship are shutter failures.].
The result is, apparently, that all minimum-radius occurs at the leftmost side of the plot – i.e. at or below 28000 – this is not at all close to what we use from the scripts. What is going on?
Is the fitting of a profile a bad way to estimate best focus?
Is the setting of the focus from the System INI file misunderstood somehow?
The start of the script used to run these tests is here:
SETDATASOURCE,PROTOCOL,,,,,,,,
CCDCOOLERON,,,,,,,,,
SETIMAGEREF,0,0,,,,,,,,,,,,,,,,,,,
STARTCYCLE1,10000,,,,,,,,
WAITMINUTES,0.01,,,,,,,,
ENDCYCLE1,,,,,,,,,
PROTOSEGMENT1,,,,,,,,,
SETDATASOURCE,PROTOCOL,,,,,,,,
CCDCONFIG,CCDCONFIGSETUP-DEFAULT,,,,,,,,
CCDINIT,,,,,,,,,
OPENEXTSHTR,,,,,,,,,
IRISOPENCLOSE,OPEN,,,,,,,,
TRACKSIDEREAL,,,,,,,,,
SETMOUNTRADEC,15,45,00,02,18,57,,,,,,,,,,
MOVETOCOORDS,,,,,,,,,,,,,,,,,,,
STARTCYCLE1,1,,,,,,,,
DOMEAZ,,,,,,,,,,,,,,,,,,,
SETFILTERCOLORDENSITY,VE1,AIR,,,,,,,
SETFOCUSPOSITION,FOCUS090,,,,,,,,
SHOOTDARKFRAME,0.0762,1,512,512,DARK,,,,
SHOOTKINETIC,10,5,512,512,VE1_FOCUS090,,,,
SHOOTDARKFRAME,0.0762,1,512,512,DARK,,,,
DOMEAZ,,,,,,,,,,,,,,,,,,,
SETFILTERCOLORDENSITY,VE1,AIR,,,,,,,
SETFOCUSPOSITION,FOCUS091,,,,,,,,
SHOOTDARKFRAME,0.0762,1,512,512,DARK,,,,
SHOOTKINETIC,10,5,512,512,VE1_FOCUS091,,,,
SHOOTDARKFRAME,0.0762,1,512,512,DARK,,,,
etc etc and then next filter.
Anyone? Help?
