GRS - Astroavani Great Red Spot (GRS) movie project · Astroavani - Avani Soares · ... · 4 · 77 · 4

These are superb images Avani. Please see my response to Almir regarding my process, which is very similar to his. I have recently upgraded to the C14 from the C11. I have used the Powermate 2.5X with the C14 and achieved my best images, so I was interested in your comment that yours were worse than with 2X.
In terms of which focal length multiplier to use, I believe you should target a Nyquist multiplier of 3 to get to the theoretical (Dawes limit) of your scope. Why? ……because the speckle imaging technique we use, when the seeing is good can get us close to the optical resolution limit of the scope. So for a C14 the Dawes limit is 0.33 arc seconds, so you should target 0.33/ 3 = 0.11 arc seconds per pixel. Actual resolution per pixel = 206 x pixel size (microns) /(Scope FL(mm) x FL multiplier). So to achieve 0.11 arc seconds per pixel you need an optimal FL multiplier of 1.8…….very close to the 2X you use. :-) So yes if you use the 2.5X you will be oversampling, just dimming the images and reducing your frame rate. Do you agree? Does this make sense?

For my ZWO the pixel size is 5.9 microns, getting towards twice the size of your pixels. So my optimal FL multiplier is 2.8X. I could probably go to 3X instead of 2.5X, as I am slightly under-sampling.

Friend Niall!
First of all I want to tell you that I have extreme difficulty with English, I depend exclusively on the translator, so this may be a bit detrimental to the exchange of information.
I fully agree with your arguments above regarding both my setup and yours as both fully confirm the theory.
Currently I keep the Powermate 2.5X only as a feature to use with a C11 or a C8 that I have for field trips anyway so far the PM 2X has always given me better result.