Constant magnification jumps means the magnification steps between eyepieces narrows by % as you approach high powers. Since the atmosphere is usually the limiting factor at high power, this gives you a way of sneaking up on the night's limit slowly and optimizing the high power. I notice many planetary observers have sets less than 1mm apart in the shorter focal lengths.notFritzArgelander wrote: ↑Thu Jul 22, 2021 7:28 pmYeah, I just don't buy constant magnification change as a good guiding principle. Apart from a 5mm exit pupil being essential for some objects really old folks find that 6mm exit pupil might be a goodDon Pensack wrote: ↑Thu Jul 22, 2021 6:43 pm To be honest, it's hard to see a difference in magnification <30x between eyepieces.
That means the 15mm and 12mm are essentially duplicates.
And you certainly don't need a 20mm for in between the 26mm and 15mm.
A constant magnification change could be: 24mm, 12mm, 8mm, 6mm, 4.8-5mm, 4mm.
26mm is close enough. I don't think you need the 15mm, though having an "extra" eyepiece is OK.aperture stop if they can only dilate to 5mm. Fortunately I'm not that old yet and can still find a 6mm exit pupil useful.
I still find exit pupil increments at the long end and focal length increments shorter than 2mm exit pupil to be a better principle for optimizing by object and sky conditions both. Constant magnification increments might make an adequate minimalist set but it won't optimize performance. YMMV.
And a constant magnification jump at the bottom end assures that when you change magnification, you will see a difference that matters. If you are looking at an object at low power and see it's too small, you want the next eyepiece you pick to provide a realistic increase in size from the previous eyepiece, not just a tad. How many eyepieces do you need at 10x/inch of
I owned about 150-180 eyepieces while I owned an 8" scope, and I found a difference in magnification of about 50x to be ideal. Less than that, and the change wasn't significant enough. More than that, and I wanted an eyepiece in between.
That wasn't a minimal set in that scope because my seeing conditions allowed 300x to be used a lot, so it was a six-eyepiece set I settled on. A lot of the fluctuation in my set had to do more with finding the ideal eyepiece for me at the magnification I wanted.
I have performed the same experimentation with my 12.5" and 4" and find the optimum jumps in both to be fairly even steps as long as apparent fields are similar. Unfortunately, the makers of eyepieces don't seem to shrink the gaps between focal lengths enough at high power to allow the slow crawl up to the seeing limit--you end up having to pick multiple brands and models to do so.