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Telescopes sold in USA usually have inches as a size
In Oz that is often in millimetres.
So a 150 will be a 6" - this is the size of the big end or mirror (showing the light gathering capacity.
For a refractor 6 inches (150mm) is the limit as they get too expensive after that.
diam area refractor ……….. area sct
2 ……….. 3.142 ………..
4 ……….. 12.568 ……….. 9.426
5 ……….. 19.6375 ……….. 16.4955
6 ……….. 28.278 ……….. 25.136
7 ……….. 38.4895 ……….. 35.3475
8 ……….. 50.272 ……….. 47.13
9 ……….. 63.6255 ……….. 60.4835
10 ……….. 78.55 ……….. 75.408
As you can see the light gathering capability goes up quite dramatcially at 8 inches.
A Dob at 8" will give you a great look at the sky - whereas a small refractor will give you good portability but not as much view.
If you go expensive you can add goto which will give you the added luxury of asking it to show you a particular patch of sky or object and not have to learn where it is or how to point
an 8 inch dob is about 6 hundred dollars an 8" refractor is 6 thousand
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