Strehl ratio and wavefront values, how important a

I also am considering a higher end refractor or a solar scope (not both). I just want to understand the quantitative values above and how they impact the viewing experience. I have an Orion 80ED and when I look at the moon it is crystal clear (what else is there?). I'll grant you it doesn't have the ability to see deeper like a larger refractor, or reflector does, but I'm just trying to see the value in these two benchmarks and practically what they represent. It kind of reminds me when the audio industry would market "THD" or total harmonic distortion, which to me was some marketing hype, the reality is if your hearing is damaged from working around power equipment etc. its pointless to go for some ultra expensive speakers/system because your ears will never perceive the 'fidelity'. I have 20/20 and 20/15 vision and I'm in my early 40's what I've noticed in the last 5 yrs. is how my night vision has worsened. I used to get up in the night and be able to make it around in a completely dark house with ease, now I have to proceed more cautiously. When I look at this scope: http://www.astromart.com/classifieds/details.asp?classified_id=363494 , (which must have superlative optics and a premium added to the price for the high benchmarks) I just want to know if when I look through the eyepiece if I am going to perceive any difference, otherwise whats the point? I'm very pragmatic and if there is no added value then I don't need to waste the money on something that is I guess only for bragging rights. Thank you for the replies and any clarity (no pun intended) you can offer.

Also what are the minimum strehl and wavefront values that are desired before the viewing experience is affected and what do you start to "see" when these values become inferior?

There is some simulation software called Aberrator you can download and have fun with. You can try "looking" at Mars with different grades of optics. The Strehl numbers are not directly given, but you can read them off the PSF/EE plots where the red PSF line intersects the left axis. It is a little work to install, but you can have great fun with it.
http://www.apm-telescopes.de/englisch/index.htm
under "telescope aberrations"

Optical quality is certainly a matter of personal taste. There are times when it is just nice to look in any telescope at some nice nebula or galaxy. And there are other times when it is nice to push the optics and conditions as much as possible -- to see some detail on Io or Enke division or Sirius B. In the second case best optics helps, and maybe you also go thousands of miles for good seeing, and use very best eyepieces, etc.

Probably much better than 1/8 or 1/10 wave peak-to-valley of spherical will be hard to tell much difference, and that would be around Strehl 95%. My experience -- with careful star testing of images outside focus, you can probably see errors to Strehl 97%-98% but that is not real observing (only testing).

Maybe if Roland wanders through here, he can offer some expert opinion....

Gary Smith said:

I also am considering a higher end refractor or a solar scope (not both). I just want to understand the quantitative values above and how they impact the viewing experience. I have an Orion 80ED and when I look at the moon it is crystal clear (what else is there?). I'll grant you it doesn't have the ability to see deeper like a larger refractor, or reflector does, but I'm just trying to see the value in these two benchmarks and practically what they represent. It kind of reminds me when the audio industry would market "THD" or total harmonic distortion, which to me was some marketing hype, the reality is if your hearing is damaged from working around power equipment etc. its pointless to go for some ultra expensive speakers/system because your ears will never perceive the 'fidelity'. I have 20/20 and 20/15 vision and I'm in my early 40's what I've noticed in the last 5 yrs. is how my night vision has worsened. I used to get up in the night and be able to make it around in a completely dark house with ease, now I have to proceed more cautiously. When I look at this scope: http://www.astromart.com/classifieds/details.asp?classified_id=363494 , (which must have superlative optics and a premium added to the price for the high benchmarks) I just want to know if when I look through the eyepiece if I am going to perceive any difference, otherwise whats the point? I'm very pragmatic and if there is no added value then I don't need to waste the money on something that is I guess only for bragging rights. Thank you for the replies and any clarity (no pun intended) you can offer.

Also what are the minimum strehl and wavefront values that are desired before the viewing experience is affected and what do you start to "see" when these values become inferior?

Conversations with TMB lead me to feel .96 is "good enough" Beyond this, you're mostly buying bragging rights unless you're gonna be able to observe from space.

A few weeks ago, Markus posted something on the TMB group that indicates the lens tests on TMB objectives should be considered as a "no worse than" figure.

Somebody had their objective critically tested for Strehl and a lens LZOS tested as .952 tested as .989

When Markus checked with LZOS they told him it would be more expensive to make sure every lens was perfectly installed on the interferometer to get the highest possible rating.

I have a TMB 115 CNC and love it.

A friend has a 130 f6 CNC and it's also a very nice scope.

The different mirror and lens makers all seem to have different ideas on how to get the "numbers". They never seem to agree on how to get them. So I gave up on the numbers game, I just don't care anymore. What I do now is buy my scopes from compaines that I feel this won't be an issue. If you buy from the best you know you are getting the best. The numbers don't matter, the scope will work to the highest standards. I also feel that even with great numbers what is of the utmost importance is the micro polish. You can have great numbers, but if you don't have that great polish, contrast will suffer. In a mirror without that great polish you won't get that nice black background we all love.