Extending the lower limit on the search for a good focus we now have a preliminary result for the B filter:
The plots show various focus-related quantities against focus position. The first two panels shown (on lin-log and lin-lin scales) the radius of the fitted Moffat profile. The next shows the standard deviation of the image, divided by the mean value of the image, the fourth box shows the exponent of the fitted Moffat profile, and the last box shows the vertical scale (height, really) of the fitted Moffat profile.
The various properties – which should all be maximum (or minimum) at the best focus – indicate values of best focus from 24500 to 26000, with 25500 being perhaps the least uncertain.
The focus we use at the moment for the B filter is 28250 – outside the range found here. That value corresponds to almost a doubling of the width of the Moffat profile.
We do not understand how the setting can be that much off – possibilities include that something happened during transportation or that the addition of the heater has changed the focus position.
Perhaps Ahmad has an original INI file from the days in Lund and could check what value was found best a year ago?
Perhaps Torben could see Torbjörn, or whoever understands the mechanical design in detail, and ask whether the heater could be warping the optical bench? Temperatures to 60 degrees C is seen on the clip-on thermometer in the dome.
The good news is that if better focus positions can be found for all filters in the above way then we should be seeing less fuzzy images in the future – it seems we have a FWHM PSF now that is about 2 pixels.
