Hi Mike,
There is lots of test information available about the scopes in question here to be able to look at, except for the R30. We can only go on the marketing claim that you guys are making.
I would also disagree with using the word "statement" here as it's seems to imply fact and you are correct about that, we have no facts about the R30's. What I would more say is we are seeing commenting on and making observations of data available. We are also using deductive reasoning. And of course there is some personal opinion.
But since we are talking about Neil's review of the R30 here and the tests he did and observations he found, and that I have brought up the alternate Synta 120ED and shared some observations and opinions on that, let me share some of the facts here since we have them available.
Below is an example of the Synta 120ED and a 4" F15 achromat that Mr. Rohr has said had good color correction. Note that Neil stopped the R30 down to do a comparison test against an achromat of similar spec:
www.microsofttranslator.com/bv.aspx?from=de&to=en&a=http%3A%2F%2Fwww.astro-foren.de%2Fshowthread.php%3Fp%3D42386%23post42386www.microsofttranslator.com/bv.aspx?from=de&to=en&a=http%3A%2F%2Fwww.astro-foren.de%2Fshowthread.php%3Fp%3D34665%23post34665The Synta 120ED has only 0.2mm of color error. It did even better when used with a prism and achieved 0.12mm. Very impressive!
The 4" achromat showed a defocus of 0.824mm of defocus.
Remember, we are effectively having a mathematical discussion here. If the R30 is 30% better than the standard achro, then it should be able to do 0.576mm of defocus. But even at that, it is obviously no where close to the color correction performance of the Synta 120ED. Is that figure similar to what you are seeing with the R30?
But taking this farther and looking at Neil's test results, we see some interesting comments. He mentions a "creamier" appearance to the image in the R30 as compared to the standard achro. Creamier to me means more yellow, and the yellow color has been reported by other R30 users.
Looking at Roland's article on color correction in refractors, we see his comments that the better the color correction, the more white the image. And conversely poorer color correction shows as a more yellow image. I can say from my own experience in testing refractors, this is true.
geogdata.csun.edu/~voltaire/roland/color.htmlSo, going back an looking at Neil's comments, one logical conclusion is that a more yellow image in the R30 as compared to the achro means that it has worse color correction. But, maybe there is another explanation.
What it ultimately comes down to is needing to see the hard details on the R30 in terms of what is the color defocus for the various channels. Note, this isn't the glass that's used or the curves of R1-4 or other design details, but the real world performance.
Are you guys going to share any performance information other than the 30% improvement statement? As I pointed out above, an approximation can be gained still from your claim, but the field reports are also showing some open questions around that as well.
Look forward to hearing more!
Clear skies,
-Gord
