Orion Optics-Fim ending europa,SPX e dobson range?

[sixela]

These numbers etc are all very interesting, but in real terms, where will the differences be seen between a 'normal' mirror, and a fandabidozy mirror?

First of all, it depends on the error.

Roughness will lead to slightly more veiling glare from objects far away from what you observe, errors in the figure will make the image slightly more blurry at high powers ("high" being between 1.5 and 2 times the aperture in millimetres).

Everything which you observe with night vision is relatively unaffected by small figuring errors (your night vision is very blurry). The first thing that would suffer is the star images (if you like looking at open clusters a lot) and first and foremost low contrast features on planets (like Mars and Jupiter).

But it all depends on the relation between the seeing and the size of the scope. A 16" scope is almost never diffraction limited where I live; you have the thermal behaviour and the seeing as two hurdles. So differences that would only reveal themselves at magnifications over 600x-800x are, sadly, things I don't see every day.

Just to give you an idea of how unimportant Strehl ratio differences are once you have a "good" mirror (Strehl ratio of 0.93 in this case), here are two Aberrator simulations of what Jupiter would look like without the atmosphere to blur the images (including anything that has to do with mirror cooling).

The scopes are 150mm aperture scopes and have a 10% obstruction (if the scopes have more, small differences in the mirror make less difference). The image was produced when someone was saying that it was completely improper to leave a 6" f/10 spherical because of the Strehl ratio of .93 that "only" yielded:

[Yes, that's what a 150mm scope could show you --well, if the image didn't become dim at very high powers and floaters didn't get in the way. In real life you have to stand away as indicated to get a more accurate idea.]

I hope the image conveys why I'm not a Strehl ratio fetishist, and why I meet someone who claims he couldn't split the double double with his 300mm mirror because the Strehl ratio is "only" 0.93 with some incredulity.

Surprisingly, at the camera in planetary imaging it matters even slightly less, because wavelet processing will actually partially reconstruct what a small amount of spherical aberration produces.

Roughness, on the other hand, is almost completely irrelevant to planets and the star images, but if you want to observe something only slightly fainter than the sky background you really don't want sources far away to scatter even tiny amounts of light and convert those to veiling glare (i.e. an increase in the sky background brightness).

But to be honest, that only matters in a scope where the baffling and flocking is perfect, because improper baffling will cause a lot more veiling glare than a mirror with some microroughness. I've seen people throw money at a SuuperDooper mirror with 0.99 Strehl ratio only to mess up the basic design, and that's a bit like putting an excellent engine on a car with square wheels.