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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Telescope Terms Dictionary
http://www.hioptic.com/knowledge/telescopes/index.htm
Telescope Basics - Eye on the Sky video series
http://www.eyesonthesky.com/Videos/TelescopeBasics.aspx
When I was looking for my first telescope I was confronted with the same flood of information. Here is how I break it down in the most unscientific way.
Shorter focal length, FL = wider field of view FOV, but lower magnification for any given eyepiece.
Longer FL = narrower field of view but higher mag for any given eyepiece.
I started with binoculars and LOVED the wide views but wanted more magnification. So when I got my first scope I wanted to maintain some of that wide view so I went to a short focal length scope. 400 mm.
My 10X50 binoculars gave me a 6 degree FOV. If I went to 15X70s I would have gotten higher mag and 4.4 degree FOV but they are hard to hold steady and good binocular mounts are expensive.
So I went for a 400 mm FL scope that gives me 15X and 3.4 degree FOV with a 26 mm plossl eyepiece. I still get a fairly wide view with rock steady image. And I can swap out the eyepieces to get higher magnifications, something I can't do in binoculars.
My 80 mm refractor is useful between 15X and about 160X depending on how bright the target is.
So, if you want wider views you go for shorter focal lengths. Many longer FL telescopes are limited to 1.5 degree FOV or less.
The same apertuere telescope with a 1500 mm FL, with that same 26 mm plossl eyepiece would deliver 57X and .9 degree FOV. So you only see a very small amount of sky.
You will sometimes hear people say that this scope is good for planets while this scope is good for deep sky. There are many factors that can contribute to that but part of it is the FOV vs. magnification delivered by the telescope. Planets only require a fairly small FOV but a lot of magnification.
Many deep space objects benefit from wider fields of view and not as much magnification.
Both short and long FL scopes can be used for both kinds of targets but one is better for one type and one is better for the other type. I have spent many evenings observing Jupiter and Saturn with my 400 mm scope and enjoyed it a lot at 120 - 150X.
Note that how much magnification you can use is limited by your aperture and often limited by atmospheric conditions. I have eyepieces for my 8 inch/203 mm Dobsonian that will give me over 500X but the atmosphere often limits me to 250X or less.
I hope that was helpful.
As for astrophotography, I am not an expert in this field but for the most part the main focus in that part of astronomy seems to be more around the mount that can track the sky than the OTA, optical tube assembly, what you would think of as the telescope. So, often you see big expensive mounts with relatively small OTA.
Then there is electronically assisted astronomy, an area I am just starting to dabble in, it seems that the shorter FL, lower focal ratio scopes on tracking mounts are preferred. I am setting up my 400 mm FL 80 mm aperture refractor Goto scope with a video eyepiece system called the
Revolution Imager R2. That will be my EAA scope. My 8" Dobsonian, which does not track, will be for visual observation.
me too...
