|
Hi all,
As Terry says, a newtonian & a schmidt-cassegrain are different beasts, with respects to their 'traditional' focal ratios.
Typically, newtonians would have an upper focal ratio of around f/8. The lower ratio for an SCT would be f/6.3, there by implying an overlap.
Each optical system offers distinct pros and cons, as would be expected. I'll just give an overview of these technicalities and leave it to you to choose your weapon.
* The secondary obstruction of a newtonian is smaller percentage wise than that of an SCT, giving better contrast.
* The slower focal ratio of the SCT gives better views of the planets, and the prime focus image of the planets is likewise larger for the same apeture.
* The faster newt provides brighter images visually and reduced exposure times, both for DSO's.
* No spider in an SCT means no diffraction spikes around bright objects in images taken by an SCT.
If you are trying to decide on a particular set-up, you need to make a judgement call for yourself on the balance of optical properties. No single scope is a 'one-size-fits-all'. Off cause there are optical aids, like barlow lenses and focal reducers, but these add to the cost and put more glass between you and the universe.
I own scopes of both types. Though I don't do imaging, visually they each offer unique properties. Choice of which scope touches the night air depends on the observing plan for the night.
Physically they are also different, but that is not your question.
|