Reflection for dim galaxys

[Hakann]

Topics on reflection.

The star party I went to in Sweden last weekend I had a the topic up on silvering optics as this was showed on the Oregon SP this year.
As I got it, silvering reflects better than aluminium, but after read about it, I’m not shore.
Its a astro club here do aluminium costings with good results at Uppsala university.
Ok aluminium less s overcoat do not get over 90% but last several years.

One in Sweden that was at the SP now had send his 16” mirror to a UK company before as the idea was get more reflection out if it, but they damage the mirror totally for him.
Its was recoated by the club here and I has look into it before and its nice stars/contrast as a example a CZ at f/4 by using Ethos 13 mm.

I knew CZ do aluminium with coatings, and not ’enhached’ coatings.
Guess he is little over 90% and last for years.
As I got it, aluminum/engached will get 95% and be Ok if done the right way. ( and as I got it, its hard find one that can do it right )

I’ll read on silvering and it was told to reflects up at 400 nm at 85% and at 500 nm 90%.
But with a costings and UV coatings/enhached it could do 98%.

I do not know life span and price on that, but I guess rather pricy.
So one can ask this, will it be a gain going from aluminium with ocercoat to silver with overcoat UV ? ( say a gain at +5% ) and the pice is secondary in the question.

My CZ 18” in Quartz with his coatings on ( 14;1 factor ) at f/4 with a Antares 4” Quartz diagonal is a ’overall telescope’ that will has a paracorr on and Ethos EP.
Feet on ground and star-hop/push-to vs ’help’ ( no tracking ) in a SDM chassie and all parts in CF less the chassie parts in plywood.
A fun eye candy instrument, still decent area for light to get in.

Next telescope will be a faint fuzzes galaxy haunt only 30” instrument.
Idea is less obstruction at only 11% and no coma corrector and Delites EP and at f/4 and the range of 15-20X per inch in MagX.
-Who will do the parabola is not set or material ( or design )
I can get a Pyrex 19;1 blank at ruff f/4 but I’m not shore vs sag here.

A question here vs the reflection.
My guess the parabola figureing is the king and no sag ( design ) but how about reflection for this faint fuzzes observing ?

Is the silvering as good vs the eye as anything, even if the nm range is not at 550 ? ( note, dim galaxy use )
So what about 90, 95, 98 % ?

Dim galaxys might like a real nice reflection.
Maybe its more imprtant than the very best figureing at a pupil at 1.5-2 mm ?
I’mean 15X per inch is not really high power and dim galaxys is not like planets.
Ok, even 15X require some good sky ( I’m aware, so this is at LaPalma - not Sweden use )

If I was into split stars only I could use a good smaller refractor.