I mentioned previously that I had switched over temporarily to a borrowed 12″ F/8 LX850 OTA. I didn’t mention that it was a prototype incorporating a proposed new feature – installation of a forced-air setup comparable to previous 7″ and 16″ LX200 models. I’ve been using it and trying to get a feel for how effective the cooling is compared to the three 12″ F/10 Meades I owned previously, though of course without a controlled, side by side A-B test the result won’t be definitive. The fan has been running during all of my imaging runs, to take advantage of whatever improvement there is.
The other night, I tried something different. I took a series of ten 5 second exposures with the fan off. I then engaged the fan and took ten more. Then I repeated both sets. That gave me 40 exposures, 20 each with and without the fan spinning. I knew that over such a short term I wouldn’t see any cooling effects but I wanted to establish that there was no more issue with fan vibration than in any of the other cooled Meade tubes I’ve owned. There was a lot of variation from frame to frame due to early evening urban environmental cooling effects so I examined the data in sets. I ran the sets through CCDInspector and derived the following FWHM values for each set:
first series without fan 2.26 arcseconds
first series with fan 2.32 arcseconds
second series without fan 2.46 arcseconds
second series with fan 2.38 arcseconds
average of all with fan 2.35 arcseconds
average of all without fan 2.36 arcseconds
I conclude from this that fan vibration is having no effect on star images.