How bad is 1/3 wave mirror?

Hi!
I'm planning to build a fast newtonian as a grab n go scope. Maybe 5" f/5 or 6" f/5 from Meridian: http://www.meridiantelescopes.com/primary.htm. This will be for low power viewing. What performance can I expect from these mirrors?

Thanks,
Joel

Joel:

This is my thinking:

If you are going to go to all the trouble of building a scope, start with a good quality mirror. By the time you are done with the scope, the cost of the mirror will be a minor concern when compared to the effort and expenses of all the other components, mirror cell, focuser etc.

At low magnifications these mirrors probably will do quite a reasonable job but a decent 5 inch F5 or 6 inch F5 mirror can do wonders at high magnifications as well. If you are out there looking at the Milky Way, why not have a scope that can split Antares if you so desire??

One thing to consider here is that while you might get a mirror that is better than 1/3 wave, you also might get one that is worse. IMHO important point to recognize is by specing 1/3 wave criteriathey are saying that these mirror DO NOT meet the basic diffraction limited criteria.

Jon

Buy a better mirror, at that size the cost difference will not be that great. Plus, why build something using all that energy, that you will want to improve later. 1/3 wave converted to wavefront is not even 1/2 wave, so low power would work, but not much more.

1/2 , 1/3 wave optics mirrors. Ever own and Celestron or Meade scope. Chances are very good you'll get one of these optics

Clear Skies
Dwight L Bogan

Joel Munoz said:
I'm planning to build a fast newtonian as a grab n go scope. Maybe 5" f/5 or 6" f/5 from Meridian: http://www.meridiantelescopes.com/primary.htm. This will be for low power viewing. What performance can I expect from these mirrors?

That depends on what they mean by 1/3-wave mirror. If they mean that its surface is accurate to 1/3-wave, that's pretty bad indeed, since the error in the image will be double the error in the surface--i.e., 2/3-wave.

If they mean that the "wavefront error"--the error created in the image as a result of imperfections in the mirror--is 1/3-wave (meaning the mirror's surface is accurate to 1/6-wave), that's merely a mediocre mirror.

In any event, I would forego any place that says 1/3-wave is pretty good. It may once have been, but these days, you should be able to find a promise of 1/4-wave, and have a reasonable chance of getting it, too.

Robert Apruzese said:

Pretty darn bad.

I wonder. A mirror that is true 1/4 wavefront and nice and smooth actually works fairly well. Perhaps not quite "Pretty darn bad."

Clear skies, Alan

Hi!

Thanks to all for your response! I do realize now that this isn't the way to go. False economy. Anyway, I found another source which says their mirrors are 1/8 wave.

http://www.e-scopes.cc/

A lot more expensive but I agree with the previous posters that since I'm going thru the trouble, I might as well start it right.

Thanks,
Joel