Better secondary Mirror upgrade to increase resolution?

[AstroGuy]

Hi,

Just wondering if anyone has ever thought of upgrading their secondary mirror in a reflector setup to increase resolution?

Considering that the primary error wave specs of your scope's primary mirror is whatever and your secondary mirror error wave specs are whatever.

Would it not allow more resolution and less error if you could find a secondary mirror with error wave specs that are better than the one you have now?

This would definitely work I think especially if the error wave spec of the secondary is less than the primary error wave spec.

for e.g.

If Primary mirror error wave spec = 1/12

and

If secondary mirror error wave spec = 1/12

getting a secondary with error wave spec such as 1/13 to 1/20 would increase resolution, right?


What do you think?



Regards...

[DavidU]

In real terms I think Quarks Saturn images have had a great boost in resolution since he up graded to a very high spec secondary mirror.
His 16" Meade main mirror is probably not a super hi spec one.
I think Trevor may have some info on this.

[Quark]

Hi Eugenio,

I think a very high quality secondary does make a difference.
I have a thread on the ATM forum on my new Planetary imaging scope "FRED", have attached a link to it.

http://www.iceinspace.com.au/forum/showthread.php?t=71332

Regards
Trevor

[Satchmo]

I think a good deal of Trevors improvements in image quality are due to the new oversize aluminum tube replacing his old cardboard `heat sink '. Increases in flatness on a flat have much less effect on improving Strehl ratio than making similar improvement in spherical aberration on the primary mirror. I once saw a simulation of 1/2 wave P-V curvature on the secondary on an otherwise perfect 16" Newt and the Strehl dropped to only about 0.94. On the other hand if your flat is only really half a wave then theres a 6% gain you can potentially get by replacing it.

I've tested loads of diagonals and particularly in the larger sizes they would average 1/4 wave. I think the high specced ones from Antares are good value. Even a 1/12 wave flat that was genuinely so would enable you to pick up almost as much advantage as was to be had with a good secondary. 1/30 wave secondaries are for the purists only- and I guess planetary imagers are amongst the purists. Remember that an optical system can only be as good as its weakest link :)

Perhaps I will get to test Trevors old secondary sometime and the reasons will be clearer .