Quote:
Originally Posted by ericwbenson
I think those numbers are incorrect. I dug out the original report from Hogg 1965 (see attached PDF), and he talks about a CARSO Automatic Seeing Monitor and a Danjon 'to' parameter (the latter needs to be multiplied by 2 to be somewhat equivalent to the former). I don't think either can be interpreted as the FWHM we measure with our modern sensors.
A project I have been thinking about is adding more fans to the CDK20 to cool the mirror better/faster. The later model CDKs (17/24) have extra fans on the side of the tube, alas mine predates that innovation, I wonder if it makes a big difference.
EB
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my understanding is that Danjon related the observed diffraction pattern in a 160mm refractor with properly measured seeing - presumably as a way to obtain remote seeing estimates with only a single portable scope and an eyeball. As you point out, it is a half angle measure and not really directly comparable to our FWHM.
CDK front fans will cool the mirror quicker, but they should also help to break up the boundary layer that forms on the front surface of a warm mirror - discussed in some detail in the earlier linked paper. Haven't yet got up enough courage to let the hole saw loose on my CF OTA and put in some front fans, but I am pretty sure it will be worth doing. Your scope represents about 50x my investment, so I guess you would be even more reticent to cut holes in it
