I thought I might place some facts about my telescope here for my readers and how it works.
There are 2 main types of telescope, refractors and reflectors along with several sub-groups for each that I will not go into. My telescope is a reflector, specifically it is a schmit-cassegrain telescope, SCT for short. I made a small drawing in paint to show how it works internally.
*The above depiction is simplified. There would be many more angles as all the different wave lengths would reflect at different angles due to the refraction of the light by the corrector plate so that in the end all the light focuses at the same point. I know I stress this several times but it is important to understand.
Basically light goes in the front of the telescope through the corrector plate, reflects off the primary mirror to the secondary mirror where it is reflected down through the baffle towared the eyepiece. If the corrector plate were not there to slightly refract and correct the light, the image seen would have some chromatic aberations seen as color fringes around some objects. This is due to the fact that every color has a different wave length messured in nm (nano meters). Red has a wave length around 650nm while blue has a wavelength around 475nm. Consequently shorter blue wavelengths scatter more easily when encountering molecules in the atmospere than longer wavelength do. This is why the sky appears blue during the day.
The purpose of a telescope, contrary to many beginners beliefs, is not to magnify but to gather light. The point where light enters the telescope is often referred to as the objective or aperture. The larger the aperture the more light it can gather and focus into our eye. In this way we are focusing alot more light photons into our eye than would normally be possible. We use eyepieces to increase (and sometimes decrease, as with a focal reducer) magnification.
The fact that my telescope reflects light several times gives it a focal length nearly 4 times the length of the actual telescope. This is a big selling point as it makes the telescope more compact and portal. (the 8inch is possibly the limit for most in terms of portabilty as the larger editions really start to get heavy, especially their mounts.
Some facts specifically about my telescope.
Aperture size: 203.2 milimeters or 8 inches. Gathers 846 x more light than the avg. human eye.
Focal length: 2032mm or 80 inches. Notice the relation between aperture size and focal length. Focal length is the distance needed to bring all the light gathered to a point.
Focal ratio: 10. The focal ratio is mostly only important for photography and is often referred to as f-stop in cameras. It is the same thing and it affects the speed of the optics. The lower the focal ratio the faster the scope (or camera lens). You can know your focal length by dividing your focal length by your aperture (focal length of my scope is 2032mm divided by my aperture of 203.2 gives me an focal ratio of 10). The lower the f number the lower the magnification and the wider the field of view. The higher the f number the greater the magnificatin and the narrower the field of view.
Highest useful magnification: 480x. This is very dependent on seeing conditions. Useful magnification is often much lower because of atmosperic limitations such as light polution, water vapor in the air, turbulent jet streams etc.
Lowest useful magnification: 28x. After which point the telescope will not be able to bring the object into focus and it will appear blurry or it will not see it at all and will only see past it.
I mentioned above that magnification can be altered by using eyepeices, in the interest of brevity I will not go into how the eyepeice changes the light path creating longer or shorter focal length increasing or decreasing the magnification. I will just list my current eyepeices and the magnifications achieved by using those eyepeices. Every eyepeice has a number on the side in mm which is it's focal length, we can calculate the magnification by dividing the focal length of the telescope by the focal length of the eyepiece.
25mm eyepiece: 81.2x
9mm eyepiece: 225.7x
I also have something called a barlow or doubler this will allow me to reach 451.5 magnification.
I also have a focal reducer that reduces the focal length (and hence the magnification) by a factor of .63 allowing be to bring my 25mm magnification down to 51x. The purpose of this is to see more sky at once. Most useful for photography.
I think that about covers it for this post.
ps. I guess this entry was not only for others but also as a kind of test for myself. I know my scope so well now that I was able to do the drawing and discuss all aspects of my telescope without having to look anything up. I pretty happy about that.