Rayleigh and Dawes mystery
Posted 08 January 2013 - 08:45 AM
Yet until now I found no paper concerning the resulting consequences for all these criterions - if the size of the Airy disk (the distance of the first minimum from the center of the spurious disk) depends on the size of CO then also these criterions are influenced.
For example Rayleigh requests sitting the secondary in the first minimum calculated with 1.22 for zero CO but with a CO of 33% the first minimum sits at 1.098 (value according to Chris Lords paper on splitting unequal doubles) and then the Rayleigh criterion should be calculated accordingly giving then 124/D_mm instead of the usual 138/D_mm. The same relation should then also be valid for Dawes etc.
What did I miss here?
Posted 08 January 2013 - 10:37 AM
I have adjusted my Airy disc to 0.84" arc and expected Dawes limit to 0.72" arc based on D/(1 - o^2). I am pretty sure I successfully observed 7 Tau at 0.74" arc (reported) as a "Dawes split." There was a contrast difference between the peaks, how much is anyone's guess. It certainly was not the classic black space, however.
The spacial frequency conversion comes from the link below (bottom.)
Posted 08 January 2013 - 12:44 PM
Posted 08 January 2013 - 09:29 PM
Posted 09 January 2013 - 08:29 AM
Meanwhile I have made an aperture mask for my 80mm refraktor with a central obstruction of about 30% - if theory works this should make an 8 from an elongation and a clear split from an 8. Next clear sky ...
Posted 09 January 2013 - 09:19 AM
Our own Mr. Cotts is getting a 200 TEC Mak for doubles, I am sure he might be interested in the subject of how well they perform on them compared to his 6" refractor. I am interested, too.
I wish someone would pick up on this topic and run with it. It's right at the heart of what I am discovering about my own scope. And double stars seem to be a good way to probe the limits of Dawes and Raleigh as well as probing the effects of a CO and residual spherical aberration (common to APOs, too, I believe.)
Posted 09 January 2013 - 10:45 AM
Please check your NEML at this session.