The limit of scopes for resolving detail is little over 30x magnification per inch of aperture, which roughly equates to an exit-pupil of 0.75mm. In summary, if you multiply your scopes focal ratio by 0.75, that's the length in mm of your highest-power eyepiece.
Use calculator: https://www.12dstring.me.uk/fovcalc.php
| ES 10” f5 | 5*3/4=4mm eyepiece; Max mag = 300 |
|---|---|
| ES 16” f4.5 | 4.5*0.75= 4mm; Max mag = 480 |