Is it worth it to refigure?

I have a 10" Newt that was evaluated by Woden optics. They say the mirror is marginaly ok. It has a strehl ratio of .93 but is said to be a little rough with a raised center 4 inches in diameter. I am unsure if I should refigure the mirror. I have to say I was a little disappointed about some double stars and when comparing to a 8" Celestron SCT the SCT has better "crispness".

The point: An Orion 10" newt should do better than the 8" SCT so I would hope to get at least to the level of an 8", right? (I am not talking about coma, comparisons were made under similar magnifications and with on axis stars and planets)

The mirror is guaranteed to a minimum specification of the following:
Strehl Ratio of .960 or higher
RMS Surface error of 8.4nm or better
P-V Surface Error of 1/18 wave or better
Should I do it?
Eric

Eric,
How much to refigure? The cost vs. return is the question. How much better would the views be refigured? Is the mirror Pyrex? This is also a big question. I don't think a 10" plate glass mirror would be a good subject for refiguring. Too much possibility of annealing problems and no return if you wanted to sell it later.
Just my opinion of course.

Eric,
When you compared the newt to the schmidt, was the newt sufficienty cooled down and quite well collimated? Newts can be pretty hampered if the mirror hasn't cooled down enough yet. Also, any chance that you've got a dud secondary? Maybe you should play around with your scope a bit more to see if you can isolate the problem. Also, do some star testing if you haven't already and check out the central zone and surface roughness for yourself. It would suck to get the mirror refigured and find out later that a dud secondary or thermal issues were causing the poor double star images.

Anyway, good luck with this!
Tim

No, don't touch the mirror! A strehl of 0.93 is very good. If the mirror truly has this figure, than your issues are either thermal issues, or a bad secondary (or collimation, etc.). I would not touch a scope that has a real strehl of 0.93 - it is equivalent to 1/6 to 1/7 Peak Valley wavefront - a good mirror.

Eric Pellegrini said:
It has a strehl ratio of .93 but...
...Should I do it?
Eric

Orion makes an OK mirror. I believe (but you need to verify) that they switch to pyrex at 10". I would tweak in a few other ways first:

1) Replace the secondary. Run through newt and check the size. On the 8", they are way oversized. I picked up a top notch secondary from Antares. You could hold the 2 up and see a definite brightness difference.

2) The Orion focuser stinks. At a minimum, change the grease. At best, replace it with a 2 speed crayford. Don't underestimate hitting the sweet spot. I personally think the focuser is what Orion does the worst. They have good customer service, an attractive product, reasonably solid build and acceptable glass. Their stock focuser is a piece of junk.

3) Flock, Ultra Flat black - check everything for stray light.

4) If you still want more and have the cash - do the primary. It's expensive, but if you plan on keeping the scope a long time and using it alot, it will be money well spent. I did my 8" and love it. The only downside is I turned around and built a 12.5". The 8" is underutilized and I have guilt because it is such a fine instrument now.

My 2 cents (before taxes).

Ed

If you decide to alter the mirror, I would
carefully weigh re-figure against just buying
a better mirror. With a cheap mirror you
do not know anything about the quality of the
glass and how well it was annealed. You may
end-up paying big bucks to put a very nice
curve on a piece of glass that will hold shape
for about a week. I once did an expensive
re-figure only to have the mirror warp badly
in the coating process. I now have an
expensive door stop to show for it. If you
have a poor mirror from a reputable source
like Orion, theres a fair chance the glass
itself is unstable or bad.

Eric,
Check these guys out........

http://www.speednetllc.com/dbaastronomyproducts/DBA%20Certified%20DSH's.htm

You may already know about them, but just in case.

Jay