[ngcles]

Hi smenkhare & All,

As others have already noted the biggest difference between the two is the native focal length of 2000mm for the standard commercial SCTs (Meade, Celestron) and the typical fl of your average commercial dob -- at f/6 is 1200mm.

They both gather almost exactly the same amount of light -- the SCT is a couple of percentage points behind becasue of the larger secondary -- but it's hardly worth mentioning.

When used visually at the same magnification, the image will be equally bright in both.

For visual use you will be able to achive a wider field more easily with the newtonian because of the shorter fl, and the flip-side is that with the SCT it will achieve higher magnifications with longer fl eyepieces which usually have wider eye-lenses and longer eye-relief that are more comfortable to use.

Because the SCT has a much larger central obstruction, it is not as visually contrasty as the newtonian but in practice, on 19/20 nights you won't see a difference when the seeing is either poor, average, good or even very good. On the 1/20 nights the seeing is excellent, an experienced observer will see more planetary detail more easily with the newtonian.

The two other considerations are the price per inch -- the dobonian/newtonian will be much, much cheaper than the SCT.

On the other hand, the SCT is much more compact, easier to store and is more compact for transport. Both will require collimation from time to time but the newtonian more often. On the flip side, it is easier to collimate a newtonian than an SCT.

If you are contemplating imaging in the future, both can be good imaging 'scopes -- there are several designs better suited purely to imaging but really are specialist imaging optical designs.

If you are interested in imaging down the track, you will need a really good mount, but the SCT because it is more compact, a little lighter and where the camera position is places fewer stressors on the mount and you can get away with a slightly "lighter" mount. On the flip side, for deep sky imaging because it has so much fl, the SCT will be a much steeper and more difficult learning curve and require much longer exposures at f/10 with more chance of stuff-ups. You can buy a focal reducer to give f/6.3. However if you decide to do your planetary imaging with video, the long fl won't hurt so much and in terms of image scale will be a little easier to use -- for planetary imaging that is.

The newtonian at 1200mm and f/6 will be much shorter exposures for deep sky stuff and more forgiving for the learner and provide a wider field -- but you should use a coma-corrector. For video/planetary imaging you'll need a barlow or powermate (or several) to get good image scale on such a small target.

There is no right or wrong. There is only what suits you and your budget.


Best,

Les D