Quote:
Originally Posted by poider
The more I research scopes the more confusing it becomes.
What are the differences between a 150mm reflector with a 750mm tube and a 150mm reflector with a 1500mm tube, I know that the main difference will be the f/number, how much does it affect the magnification abilities of each scope and the imaging, observing abilities, is one better for observing and the other photography?
what would be the better all round scope a 150mm smith cassegrain or a 150mm newtonian reflector????
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Some great comments by Wavytone, but for your specific questions: if the optics are good, then the 150mm f5 reflector you mention will probably give just as good a planetary (high power) view as the f10 version- but you need eyepieces of 1/2 the focal length that you would use in the f10 for the same magnification. (e.g.: a 6mm eyepiece in the 1500mm fl scope will give you 250x, but you will need a 3mm eyepiece in the 750mm scope for the same magnification.)
If you use the
same eyepiece in each scope, the f5 will give you twice the true field of view, but at 1/2 the power- so is generally better for DSO's that cover wide fields. As an example, a 30mm eyepiece with a 60 degree apparent FOV will give you a view at 25x in the 750mm scope with a true FOV of 2.4 degrees. To get the same power and true field in the 1500mm scope you would need a 60mm, 60 degree apparent FOV eyepiece (I don't think they even exist: and even if one did exist it would need a much wider diameter focuser- but that is another story...)
The f5 will be a lot faster for AP, and again it will give you twice the FOV with the same camera attached as will an f10.
Eyepieces can be a bit problematic for the faster scopes: an f5 scope will give you a lot more coma than an f10, and you will need better quality eyepieces or a coma corrector to get a field that is sharp to the edge. An f10 scope is much more forgiving of eyepiece quality.
The other thing to consider is the length of the scope: this is where SCT's come into their own as they are very short for their focal length compared to the equivalent newtonian or refractor. The longer the scope, the better the mount you will need to ensure a steady view: an f5 scope or an SCT will have a shorter moment arm than the equivalent f10, and thus put less strain on the mount.
Hope that answers your questions.
All the best,
Dean
(PS: like Brian and Marc, I have one of each too!
