Michael Frias said:
WHEN VIEWING THE SUN IN H-ALPHA, IS THERE ANY DIFFERENCE IN THE VIEWS OF SAY A $200.00 80MM ACHROMAT VS A $1200.00 APO? AND WHAT IS SO SPECIAL ABOUT THE DEDICATED SOLAR SCOPES?
I don't know specifically about the dedicated solar telescopes, but I can venture a guess: they are designed to correct for spherochromatism at the rather long wavelength of 656.3 nm.
In case I just spoke gobbledygook at you, spherochromatism also goes by the long-winded name of "chromatic variation of spherical aberration." What that means is that the degree to which a refractor exhibits spherical aberration varies by the wavelength of light going into it. (Reflectors are, of course, immune to spherochromatism.) It ordinarily makes sense to correct for spherochromatism near the middle of the visual range, since the eye is most sensitive to those wavelengths (about 550 nm).
For H-alpha viewing, such considerations are moot, since 550 nm light doesn't get to the eyepiece. Only light in a narrow range near 656.3 nm gets to the eyepiece, and if you are going to correct for spherochromatism in a H-alpha telescope, you should correct it for light of that wavelength.
As I said, I don't know specifically that this is what they mean when they say specially optimized. But that's what makes sense to me. If that's the case, then an apo will be better than an achromat, simply because they generally control spherochromatism better than an achromat. But you can make a specially optimized achromat for less than you can make a generally optimized apo.