One for Roland

Mr. Christen,

As I was reviewing some old threads I came across this statement by you:

"Optically, Maks have a sweetness that is impossible to match with any SCT design presently made, even if the optics of those SCTs could somehow be made perfect. All you have to do is run some of these common SCT designs through a design program like ATMOS to see the results. And it shows up on the night sky at your eyepiece."

Pardon my ignorance but could you please elaborate a little. Forgive me if this has been answered before but what is wrong with the current design of SCT's? The SCT's I found in ATMOS are pretty good. The one with the aspheric secondary (like what Celestron does) looks near perfect with strehl ratios in the high 9's. I have owned high-end Maks (up to 8") as well as SCT's (up to 14").

The C-11 I currently own is excellent in my estimation. (Thanks Robert Piekiel for your book. Everyone does not have access to a interferometer.) It defines the airy disk to "textbook" standards. A glass 250 line grating at 4 bands outside focus are straight to the edge, are of high contrast and easily seen. The knife edge image is flat. What is it that I do not understand about SCT's?

I'm asking this from a visual observers standpoint. I couldn't give a baby gnat's butt about astrophotographic/off axis performance.

Keith

Attached Image:

>>Pardon my ignorance but could you please elaborate a little. Forgive me if this has been answered before but what is wrong with the current design of SCT's? The SCT's I found in ATMOS are pretty good. The one with the aspheric secondary (like what Celestron does) looks near perfect with strehl ratios in the high 9's. I have owned high-end Maks (up to 8") as well as SCT's (up to 14").>>

Ok, you're pardoned. But seriously, Celestron does not aspherize their design - it is basically an all-spherical design, not like any shown in ATMOS examples list. Secondly, the one you show in the ATMOS design uses an F3 primary and conical secondary. Nobody I know produces anything like that (if they did, it would be quite nice).

The Celestron design is a very basic all-spherical design using an F2 primary and 5x secondary sphere. There is considerable sphero-chromatism, and with 34% central obstruction there is an automatic reduction of Strehl Ratio to a maximum of .84 if the optics are figured to infinite perfection. The Celestron design actually mimics a Dall-Kirham, with all its known field curvature and off-axis coma. The new Meade SCTs mimic RCs with no off-axis coma, but with field curvature and twice the sphero-chromatism of the Celesctron basic all-spherical design.

Either way, you are not going to get the purity of image of a first rate Mak-Cass. If you had either of these F10 systems up against my 10" aspherized Gregorian Mak, you would instantly see what is what. Even at 250x you can see the difference, and at 600x it becomes glaringly obvious. Bring your's over and set it up beside the 10" Mak. I have a 10" Meade and have had C11 and C14s here also, so i know what is what

Rolando