Hi Bobby,
Quote:
Originally Posted by Bobbyoutback
Thanks for your input Steve , splitting close doubles could show the difference a bit clearer ? maybe
Cheers
Bobby.

In terms of splitting pairs (this also applies to all other visual applications), the difference between 150mm v152mm is about 2/3rds of 5/8ths of ...
The Dawes limit (approximation) difference between say 150mm and 165mm is 0.77 arc seconds v 0.70 arc seconds. In relatively small apertures, a small increase gives a pretty small gain. 150 v 152 is a minuscule difference.
Dawes limit approximation formula: R=11.6/D where D is the diameter of the aperture in centimetres.
So for example. with my 46cm f/4.9 Newtonian the Dawes limit is 0.25 arcseconds. With the 63.5cm f/5 Newtonian, the Dawes limit is 0.18 arc seconds. Obviously enough, the seeing (virtually) never permits large apertures to approach their Dawes limit. It's a very, very rare night when the seeing is running at about 0.5 arc seconds or marginally better than that. 0.2 arcseconds is probably something you might see in the Atacama Desert, maybe once every year or few.
I think I've seen seeing better (marginally) than 0.5 arc seconds three times in my observing career of nearly 50 years in NSW. It is a bit better here where I live now than Sydney (where I used to live) that normally has mediocre seeing and rarely good or very good. I think generally, the seeing in Broken Hill is going to be better than either where I live, or Sydney, but still only rarely approach 0.5 arcseconds.
Best,
L.