Just getting back to your original post, there are currently two perfect 'double stars' that are visible and are always interesting and useful for viewing the Airy discs and first ring. If my memory serves me correctly, the diameter of the visible Airy disc in seconds of a degree, is 120 divided by the telescope's diameter in mm's. (Dawes limit) This can be confirmed when you view the discs of a double star as you can then directly compare the disk diameters to the known separation in seconds of a degree.
Castor in Gemini is a fairly bright double of 1.6M and consists of a 1.9M and 3M pair that are currently separated by 5.25". Although not a test for a 127mm Mak, it is a great double star to view the Airy discs and first ring components of two close 'in focus' star images at the same time. In my SW 127mm Mak, I see the Airy disc and one brightish ring around each of the two stars. Very close examination reveals a very faint second ring.
At the other extreme, is the double star Orion 52 that is 5.3M and consists of two 6M stars separated by 1" that is a bit of a test for the 127mm Mak and the sky conditions. In my Mak I can see this double as two very close/touching Airy discs with a single faint 'oval' ring around both stars. At this magnitude and separation, the rings are not really bright enough to be seen between the two Airy discs. Depending upon the sky conditions this double star can be a bit difficult for a 127mm scope but last night the two discs were obvious and this was confirmed by checking the current position angle of the pair at 220 degrees.
For viewing these doubles, I was using pairs of 6.4mm and 9.7mm Meade eyepieces and a Celestron binoviewer through my SW 127mm Mak. You should probably use a no longer than a 12mm to 13mm eyepiece in a 127mm Mak in order to begin to be able to see the disk and ring clearly. They are much easier to see in my shorter 9.7mm and 6.4mm eyepieces. The sketch in Post 11 is a perfect 'illustration' of what you should be seeing on a good night.
Hopefully you are having clear skies and can view these two contrasting double stars and their respective Airy discs and first rings.
Edited by eyespy, 16 January 2019 - 10:54 PM.