Hybrid Newt w/ corrector vs. Schmidt-Newt

Hello,

I have a Celestron C150-HD Reflector (the one with the corrector lens between the primary and secondary) which has served me well for the four years that I've had it. It came with a CG-4 mount which I tore down and re-lubed. It has a 6" aperture with a 1000mm focal length, and an F-ratio of F7.

How does this scope compare with a Schmidt-Newt of similar aperture? What about an 8 or 10 inch? I'd like to move to a heavier mount, and with mounts costing what they do, it seems that it's almost cheaper to buy one with the OTA rather than alone. With this in mind, I've seen some good pricing on a goto system with a Meade SN8 or SN10 on the LXD75 mount. What are the plusses and minuses of the S-N tubes compared to a regular Newt or the hybrid that I have?

If it makes any difference, I really enjoy the DSO's and would like to eventually start doing some astrophotography.

Any other thoughts you might have would be great.

Dow

>>>How does this scope compare with a Schmidt-Newt of similar aperture? What about an 8 or 10 inch? I'd like to move to a heavier mount, and with mounts costing what they do, it seems that it's almost cheaper to buy one with the OTA rather than alone. With this in mind, I've seen some good pricing on a goto system with a Meade SN8 or SN10 on the LXD75 mount. What are the plusses and minuses of the S-N tubes compared to a regular Newt or the hybrid that I have?
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Dow:

I am going to take a shot at answering your questions.

1. Hybrid Newt: My experience is that some of these adequate but essentially they are a compromise to allow the use of a fast spherical mirror in a compact scope. Optically either of the others would be a better choice.

2. S-N: These are also designed around using a short, fast spherical mirror but use a Schmitt-Corrector which is a much better solution. However in the 8 and 10 inch sizes they are F/4 which means they will still have significant coma. More importantly, from a visual standpoint, F/4 scopes are tough on eyepieces. The edge correction of standard eyepieces is "rough" because of the steep angle of the light cone. The large Central Obstruction is an issue as well, in the 8 inch it is almost 40% by diameter.

Not my choice for visual work, especially if you like to view the planets at all. Probably a reasonable choice for astrophotography.

3. The standard Newtonian. The affordable 8 inch and 10 inch Newts are F/5, a better place visually and have smaller central obstructions. As an all around scope, I prefer standard Newtonians. They do a better job at high magnifications and a good job at lower magnifications.

About the only company to make S-Ns have been Meade...

Mounts: LXD-75 or the CG5-ASGT.. I think the 8 incher is the limit for these if you want a steady mount. The 10 inchers are definitely marginal for visual work, too small for photography. The CG-5 has the 2 inch Stainless STeel legs which make it solid. I believe the Meade uses slightly smaller legs, something of a disadvantage but not serious.
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Bottom line: I think you would find either the SN or the standard Newtonian would significantly out perform your current scope.

My preference would be the standard newt but others might disagree. Your best bet is to go to a star party and look through different scopes and see what you think...

Jon