Posts Made By: Roland Christen

Thank you, guys. Tonight I gather another 4 hours of H-a photons.

Rolando

It doesn't appear that you need a Honders.

Rolando

Center crop at 100% resolution.

Rolando

Center crop at 100% resolution

Super image Gilles. You are the master of H-alpha.

Please describe how you processed the image (what kind of stretching you used to bring out the faint detail)

Rolando

FPL glasses from Ohara are exceedingly expensive and not readily available in China. Import costs for this glass are very high. I doubt that any Chinese made lens will contain Ohara glass. The Chinese have their own ED, equivalent to Ohara FPL51. If made right, the lens will perform very well, and you would not see any difference visually.

Chinese ED is limited in size to about 120mm at this time. It becomes very expensive to produce in larger sizes at the quality level needed for astronomical objectives. What drives the market for ED glass is not amateur telescopes, rather it is the camera market, and there really is no need for larger apertures in that market. Glass companies are not rushing out to produce 8", 9" and larger blanks of ED material, and will probably never do so.

Even Ohara has cut back on their maximum size to around 7". Many years ago they tried to produce ED up to 16" diameters but failed in their attempt. There are technical reasons why this cannot be done routinely, mostly because of the fragile nature of the glass and its tendency to become crystalline and cloudy while being cooled from a molten state.

Rolando

Full size crop of the core area.

Rolando

Full frame at 1/2 size

Rolando

Nice story. Wish I had one of those.

Rolando

Your lens is probably fine. I would not expect the Fresnel rings to show symmetry in anything faster than F12 in an apo lens for the various colors. It's much more important for your lens to show round extra-focal star images than symmetry in and out of focus.

Rolando