SN vs. SCT

Hi,

I currently have an old 6" newtonian (Criterion RV6). I am getting back into astronomy and am thinking about upgrading to an 8". I like the goto capabilities of the LXD55 and its price point. My main question is about advantages/disadvantages of the Schmidt-Newtonian compared with the Schmidt Cassegrain. I have thought about the forthcoming Celestron Advanced series, but several negative comments on this and other boards about the CG-5 mount have decreased my interest in that. I don't want to start a celstron v. meade debate, they both have merit. I have also thought about the LX90, LX200 or Nexstar, but the entry level price of the LXD55 is attractive as I get back into the field. Thanks,

Ted

Speaking strictly to design comparison, NOT taking into account differences in quality from make to make, etc:

SCT Advantages:
- More compact
- More focal length and in a shorter tube to boot
- Can be fork mounted, with no counterweight necessary

SCT Disadvantages
- Focuses by moving primary mirror; over time it can get 'wobbly' and 'image shift' develops when focusing
- Curved amplifying secondary mirror can amplify wavefront errors of the primary mirror and also makes for sensitive collimation if things fall out of adjustment

SN Advantages:
- Faster focal ratio, wider fields with a given eyepiece f.l.
- Rack & pinion focusing method means no primary mirror movement, no image shift
- Secondary is flat rather than amplifying, alignment issues more forgiving

SN Disadvantages:
- Longer, bulkier, less 'stowable'
- Needs full-blown GEM with counterweights, fairly cumbersome & heavy arrangement

The 8" SN is a good size for the LXD55 mount. Light transmission is a tad more efficient than the SCT with diagonal, and the wide field views are excellent with less coma than a fast Newt.

If you like GEMs (like your old Dynascope), then the LXD55 is not a challenge setting up compared to the easier LX90.
Cooldown and collimation issues are a wash. LX90 costs more for some added refinements compared to the LXD55 SC8.

The LXD55 is higher maintenance, so if you dislike tweaking backlash, set screws, orthogonal alignments, etc., then get the LX90, which also has more accurate GoTo precision.